The combination of electrochemical methods with molecular spectroscopy can provide valuable information about chemical processes at electrode-electrolyte interfaces. In particular, Raman and infrared spectroscopies have been shown to yield unique mechanistic insights into chemical reactions at electrodes by enabling fingerprinting of surface species via identification of characteristic vibrational modes. These powerful tools therefore find applications in a wide range of disciplines, including the development of electrochemically functional materials for heterogeneous catalysis, sensing, and energy conversion and storage.
In this talk I will present case studies from NPL that highlight the value of electrochemical vibrational spectroscopies for studying interfacial processes. Examples include the use of in situ Raman and infrared spectroscopy to mechanistically probe the CO tolerance behaviour of fuel cell hydrogen oxidation catalysts and to understand doping effects in electrochemical water splitting catalysts. I will also discuss strategies for improving the sensitivity and surface selectivity of interfacial molecular spectroscopy using plasmonic enhancement phenomena and demonstrate their application to investigating organic reaction mechanisms in heterogeneous catalysis. Finally, I will show how this surface enhancement can be combined with scanning probe microscopy to allow spatially resolved analysis of photo-induced interfacial processes at the nanoscale.
Presentation given at the UK Catalysis Hub Winter Conference on 18 December 2023
Really the last 10 years or so uh using Institute vibrational spectroscopy to look at uh primarily electrocatalytic interfaces but also more broadly um uh photocatalytic as well um this actually pluged in was working a minute get this thank you great thank you um so just uh just
For those of you who aren’t familiar with npl we are the UK’s National measurement Institute or national Metrology Institute um we’re public corporation part of desit the Department of science Innovation and Technology uh we’re sort of we have different uh regions across the country that we
Have have a little bit of a presence but our primary SCI is based in tton in in West London and we have something like 800 scientists although that number is probably already a lot bigger um uh across the across the country working on on on on Metrology um and we have this
Rather sort of broad um mission to provide the measurement capability that underpins the UK’s prosperity and quality of life uh that’s quite a sweeping statement what does that actually mean well we’re probably best known for our work in standards and SI units but actually remit is quite a bit
Broader than that anything where confidence in measurement uh is important and and the previous talk I think made some good points about confidence in measurement um uh and that ranges from um the sort of very basic research all the way through to product development and actually into sort of
Commerce and trade and so we sort of sit in this little um uh uh this working though uh here we go uh this little Gap between um industry and and Academia we we span the various TRL levels um and try and sort of bridge that that Gap
Being a National Institute we we we are very much aligned to government strategy so we are challenge L and so we work in these different these strategic uh areas and obviously the energy and environment region uh theme is is the one of probably most relevance to this audience
Um and the electr chemistry group at MP we we we cover a wide range of applications of electrochemistry uh uh probably starting with the the oldest area which is the corrosion area which we we’re looking at the nuclear industry and and ccus um we have some broad Pro large
Programs in in in hydrogen so fuel cells and electrolyzers as well as more recently in the batteries areas um and they’re both they’re they’re really application based areas uh and then there’s a theme at the top right that I I lead called interfacial chemistry and catalysis and that’s a little bit more
More sort of science um uh uh based rather than application based and that really underpins the rest of the work we do in the group uh trying to improve the uh the ways in which we measure and characterize these kind of materials and interfaces I have particular interest in
In hetrogeneous and and electrocatalysis um and we’ve been developing a lot of kind of capability in the last few years in spectro electrochemistry and that’s really what what I’m going to talk to you about today uh so today’s talk really um I’m just going to start by talking to you a
Little bit about why why we’re even doing vibrational spectroscopy what what what it can tell us then I’m going to demonstrate this by way of just a couple of of of case study examples re relevant to the the hydrogen Technologies area so fuel cells and and electrolyzers and
Then I’m going to talk a little bit about um how we can use uh surface enhanced methods to really probe interfaces using a technique called shiners and also a technique called turs and I’ll I’ll explain those to you as as they come up um so vibrational spectrocopy then I’m hoping I don’t need
To really explain to you what what it involves but ultimately we’re probing the vibrational structure of of a system and we’re interested in both infrared and rahmen on on on the infrared side we particularly common we’re commonly using the ATR mode attenuated total reflection mode whereas in ramen spectroscopy we’re
Typically using con focal Ren but as I mentioned we are interested in these surface enhanced modes that that I’ll come on to a little bit later so what can we learn uh using vibrational spectroscopy coupled with electrochemistry well there’s an awful lot and this this this sort of schematic
Just captures a few of the different kind of types of chemistry that we might be able to probe you can look at the actual electrode itself the actual surface of the electrode material say say you’ve got a gold oxide there you can look at that using vibrational spectroscopy you can look at molecular
Absorption you can look at molecular orientation if you’re very careful and and The Binding modes of of molecules on surfaces and you can also look at effec the electron transfer by way of monitoring what what molecules are changing at the interface of your electrode and I mentioned already some
Of the applications that we’re interested in hetrogeneous catalysis in context of electrochemistry that might apply to electrosynthesis for instance or organic Transformations using electrochemistry electrocatalysis as I mentioned fuel cells and electrolytes the big ones um and energy conversion storage we we’ve done a lot of on on lithium ion
Batteries for instance in this area as you can imagine and also just generally surface functionalization is quite an important area of application um and I I just put this slide up very quickly um because hydrogen Technologies feature quite heavily throughout my talk I probably don’t need to explain the importance of
Hydrogen um particularly in the context of of of water electrolysis being able to generate hydrogen in a very Green Way using using renewable uh electrical energy and then being able to turn the reaction the other way around and use the use the hydrogen youve generated to make electricity again and that’s a nice
Sort of circular economy kind of situation obviously that hydrogen has other uses particularly in catalysis but we’re particularly interested in in both sides both both directions of this reaction so the first case St I want to go through is is is an example where we’ve Ed Ramen and infrared spectroscopy
To look at uh uh tungsten oxide as a uh as a material to enhance the co tolerance of hydrogen oxidation catalysts so hydrogen oxidation catalysts they feature in the anode of a fuel cell so you’re just simply oxid oxidizing hydrogen the problem is if you’ve got Co in your hydrogen feed the
Carbon monoxide will absorb to your platinum Catalyst and kill its catalytic activity so you’ll get no uh no no hydrogen oxidation going on um so it’s simply a loss of active a lot of AC active sides and what will happen in that situation is in order to remove
That Co from the surface you’ll need to you’ll need to go go to oxidizing potentials effectively what is fairly well understood is that you can um uh you generate a hydroxy species on the surface of the Platinum surface at sufficiently high potentials and that Hydrox hydroxide effectively couples
With the absorbed uh Co and ultimately generates CO2 but that only happens at potentials where uh where the hydroxy species form and in the case of platinum that’s potentials as high as6 volts against the reversible hydrogen electode given that your anode is typically operating where you want it to operate
In the around 0o to2 volts range if your anode is pushed up to6 volts you’ve lost a huge amount of energy doing that so that’s pretty awful so really you want a better tolerant uh Catalyst than than than Platinum um so one of the the common examples of of improving uh
Tolerance is to use ruthenium ruthenium offers two different mechanisms of of improving tolerance one is via an electronic mechanism you get you basically sort of tweak the the the bands the the 3D orbitals or 5D orbitals rather of the uh uh of the platinum and effectively uh change the electronic
Structure of that Co Bond um that’s one way of doing it but also the the bi functional mechanism comes into play basically the uh the ruthenium you can for a hydroxide species on the surface or rather hydroxy species on the surface at much lower potentials than you can on
Platinum and therefore the loss due to that oxidation process is is is is much less trouble with ruthenium is it’s it’s also pretty scarce and pretty expensive so you’d rather not have to use ruthenium either um so there’s a fair bit of work in the literature on on
Alternative materials that you can use to to improve the tolerance of uh uh of of of platinum and and we worked with a with a company who are developing a Tungsten oxide based Catalyst really it’s a Tungsten oxide co-catalyst that goes alongside Platinum to improve its
Uh co uh tolerance um and it’s not really well understood how this works but there have been reports that the co oxidation can happen at potential as as low as 0.1 volts against RH but but how that really works is isn’t very well understood the prevailing kind of
Understanding is that tungsten o side forms these when you reduce it forms these tungsten bronzes where you get hydrogen sort of incorporated into the into the the ltis and you generate a hydroxy species again at the surface which can do this uh this c c oxidation mechanism but as I say not particularly
Well understood so we wanted to use our infrared and ramen uh sort of capability to try and understand how this worked a little bit better this slide just really shows the difference that the tungsten oxide makes to the the Co oxidation electrochemistry that you might see so
Over on the left you have the Platinum carbon case simply looking at the Vol voltametry as you’ve got a a a CO um covered electrode surface in the presence of hydrogen or in the presence of just nitrogen and in the presence of hydrogen what you see is as you go to
Voltages as as around5 volts you start to see the hydrogen oxidation process happening and then at about 8 volts you see the Co stripping completely off the surface if you introduce on the right there the uh the tungsten upside to the system uh you see a couple of different
Couple of differences first of all over on the left you see the the tungen oxide Redux processes so tungen can be can be reduced and reoxidized electrochemically and that’s what we’re seeing over sort of in the the low potential region um but also what you see is a slight shift
In the onset potential of ox of the oxidation of of hydrogen that’s because we’ve improved the tolerance towards Co oxidation or sorry the tolerance towards Co and you can see that more clearly in this sort of closeup where we’ve subtracted the background that we get about a 100 molt Improvement it’s not
The 300 molt that the literature promised us but it’s still an improvement uh in terms of the onset potential suggesting that we’ve got some some mechanism going on that’s making things better um so we looked at this using first of all Ramen spectroscopy you can do Institute Ramen Spectros be
Just in a Petri dish and some of our earlier work uh was was done using this but if you value your Optics you’ll use a cell that has a window over the top um so in this case we’re just using a commercial cell that’s from a company called reduxx me which basically
Involves having a sample then electrolyte and then a window that that that allows us to probe uh the the surface of the electrode um and in this particular case the tungsten oxide happens to to be quite active in the ramen because the the tungsten oxygen
Bonds do light up in in in in ramen spectroscopy and they are sensitive to the oxidation state of the tungsten so this is a sort of spec Spectra that we get uh from from Institue rahen um we we typically start at an open circuit potential and you can see the Spectrum
At the bottom there um and you can see bands that we assign to tungsten oxide bending and and stretching modes um and then we start to apply a bias to the system so we start at zero volts and that immediately kills all of our uh
More most of our bands and that can be understood because we’re basically forming this tungsten bronze where you basically taken the sort of surface of the material and you’ve you’ve almost quenched your Ox O oxygen uh moities with with hydrogen or protons plus electrons um and then as you increase
The um the the potential you basically grow your bands back again and eventually at 3 point4 volts you get uh you get your original tongue oxide back in its plus six kind of oxidation state so you got your fully oxidized San oxide back so I think we we think we
Understand what’s going on here um the the key the key mechanism is that there there’s something that’s it’s just returning back to its original state at at around3 volts you can look at it a little bit more quantitatively if you just extract some data from from these those Spectra
If you look at the relative Peak intensity at the bottom there you see it actually follows kind of a stepwise transition where we’re going through different phases of this tungsten bronze and eventually at about3 volts you go from a very low intensity to a very high
Intensity so it really just sort of is a very very sudden abrupt change and you can also look at the peak position of the um one of the tungsten oxygen uh stretching frequencies and you see that that’s also undergoing a sort of a sudden stepwise shift as we’re as we’re
Changing from a pure tungsten oxide to this tungsten bronze situation but it all seems to revolve around the biggest change seems to revolve around something happening at about3 volts um so we wanted to explore this a little bit further so we we then moved on to impared spectroscopy again we in
This case we’re using the um attenuated total reflection mode where we we come in come in through the the re reverse side of a uh internal reflection element and we’ve got our Catalyst deposit on top of that reflection element um and we’re basically going to put our
Catalyst on top of that uh silicon crystal in this case saturate it with uh with carbon monoxide and then Purge Purge the system with nitrogen and we’re doing the experiment in in in in an acid electrolyte again and then we start to play with the the voltage of the system
So we apply a bias to our our cell um and there’s a lot going on here but if you compare the Platinum only case to the uh T Platinum carbon with with tungsten oxide as well you can see the probably the biggest change is the the
Line shape of the linear bondage Co on the surface is is quite dramatically different in the two cases that immediately points to potentially some kind of electronic effect which is changing the sort of distribution of electronic States in your platinum carbon um or platinum carbon monoxide
And a bond um the other thing that happens is as we change the the the potential in the system we see a shift in the in the the peak position which is very well understood as the Stark tuning effect where you basically withdraw electron density from your Co Bond and
Change its vibrational frequency and then you also see as you go to higher potentials a loss of um a lot of intensity because you’re basically stripping the co from from the surface of your uh your your platinum and that seems to be happening to a large extent
In both cases again you can look at it a little bit more quantitatively um if you look on on the left hand side uh you can see the the peak position so the wave number uh and you see it very high High uh High potentials the two systems with
And without tungsten oxide are are equivalent so not a lot not a lot is different but then as you go to lower potentials you see that the tungsten oxide case you see a sort of a decrease in the uh in the peak wave number whereas in the case of um the the
Platinum without the tungsten it’s the wave number is higher so there’s clearly an electronic effect happening there that’s causing the the sort of De deviation in in in the behavior but what’s important to note is that that that that difference is most significant at low potentials at zero volts but we
Didn’t see any improved tolerance at zero volts our our our tolerance got better at about 3.4 volts so that can’t be the reason for improved tolerance in this case so we’ve kind of ruled that out as a as a it might be affecting things but it isn’t the reason for our
Improve tolerance over on the right you can see that there’s uh there is an improvement there’s a difference in the uh the amount of Co on the surface as you get to around3 volts so the the difference between the two systems with and without the tungsten oxide is most
Pronounced at around it starts to happen at around 3 point4 volts and then it and then at around 0.91 volt the two systems are are are the same so I realized I’ve given you an awful lot of information there but uh we we pulled it all together and basically summarized that
The infrared data yes that there’s there probably is an electronic effect but it’s probably not the reason for our improved catalysis uh this the the electrochemistry combined with the ATR data tells us that there is a a sudden onset of of of uh of C removal at
Around3 volts but the ramen de data basically fortuitous fortuitously tells us that actually at the same potential there is a a sudden abrupt change in the phase of the tungsten oxide as in this tungsten br um is is changing at that point so we propos this mechanism where we have a um
Tungsten six oxidation state that then gets basically gets reduced by the co that’s in the system gets reduced to this this tungsten bronze and then that tungsten bronze only gets reoxidized back uh to to the original oxidation state at potentials higher than about3 volts and so that’s what completes the
Kind of catalytic cycle this case so we think we understand um what’s what’s going on here uh and and I think more broadly this kind of technique combination of techniques can tell us a little bit about how uh how these kind of mechanisms operate and ultimately allows us to T tune um Catalyst
Development in in future so onto the onto the second sort of case study I’m not going to go into any any real detail on this just for for interest of time but here we’re looking at um doping effects in uh Cobalt phosphide oxygen Evolution catalysts um in particular we’re interested in alkaline
Electrolysis in this case so there’s obviously a lot of work in in in in pem so proton exchange membrane electrolysis um but we’re Switching gears now to look at alkaline based systems here and some colleagues of ours uh developed this Cobalt phosphide based system and what they noticed was that when they doped
This Cobalt phosphide with um with aluminium they saw a slight shift not huge but noticeable shift in the onset potential of oxygen Evolution so the aluminium was somehow improving things but not really really well understood how um but what we noticed was that at the same time as increasing the reducing
The over potential for oxygen Evolution you know if you look at the the graph on on the right the uh the the capacitive response for the uh for the aluminium doped system was about four times higher than for the undoped system which basically tells us surface area of the
Of the the aluminium dope system is is about four times higher which if you then normalize your your electrochemistry to that surface area it turns out the aluminium actually makes things worse on an intrinsic catalytic activity level but that doesn’t matter because ultimately we’re interested in what the the catalytic activity per unit
Centimeter square is so ultimately if we’ve got a piece of material that that can can do more then it doesn’t matter whether the intrinsic activity is isn’t as good but still we wanted to understand why it was better uh we did some postmortem analysis uh which showed
That as soon as you stick this stuff in um potassium hydroxide you massively change the surface that’s that’s no big surprise um you get off all kinds of hydroxides and oxyhydroxides on the surface um we did some XPS um to show that after um some kind of electrochemical cycling you didn’t
Really see any leeching of the aluminium so it’s it’s not like the aluminium is coming out and increasing the surface area of the system the aluminium is still there in the same sort of ratio so what we really needed here was a was an insitu method and that’s where the
Insitu Raman came in um and so just a long story short really if you can look up the the uh the Spectra you you probably squint and basically see two identical sets of data but there’s not a lot of difference between the two as you go up into uh high potential so the
Oxygen Evolution region you start to see evolution of these oxyhydroxide bands and also amorphus Cobalt oxide bands but that seems to be happening in both cases and if you think about if we’re if we’re looking at oxygen Evolution conditions so up at 1.45 volts the two systems look
Almost identical so under e under under the actual operating conditions of electrolysis these two things look the same the subtle difference is actually at low potential so about 0. five and9 volts you see a peak over around five uh about sorry 700 uh w W numbers and that
Peak is actually assigned to a spinel phase of cobalt oxide so the subtle difference between these two systems is not what the end result is but it’s how it’s got there it’s the fact that the the aluminium dope system has actually oxidized via this highly structured spinel phase which is then basically
Cracked up and formed a very very high surface area electrode so that that’s what we believe is the is the reason for for the difference in behavior is not the end result but the the process by which the oxidation actually happened and and this is just showing
That the fact that actually Cobalt oxide and aluminium dope Cobalt oxide both form quite nice spinel phases so that really kind of uh helped put the the icing on the cake that this was probably the right the right answer so the the this this study really just showed us that Ramen
Spectroscopy it hasn’t really helped us understand the catalysis but it has helped us understand the root cause of the the phase changes in the material that has ultimately helped us make a better catalyst so uh hopefully that’s been a little bit a little bit interesting so um onto the sort of
Second sort of half really of my talk um I wanted to talk about using surface enhanced methods the stuff I’ve been talking about so far really we’ve been looking at the almost the bulk material I know you still only probe the top Micon or so of the electrode but it’s
Not really at the interface it’s looking at the actual electrode material if you really want to look at the interface you need to use surface enhanced methods and uh I’m going to tell you about some work we did uh first of all using a technique called shell isolated nanoparticle
Enhanced Ramen scattering shiners I should say that the vast majority of this work uh that I’m going to present was done as part of a PhD studentship with Gary ATD who was at Cardiff back uh many years ago um he’s now at Liverpool but the student Shia Lang who is in the
Audi is uh is acknowledged for all of this work because it’s all his um so a little bit of a primer in terms of what surface enhanced Ramen is so uh basically when you shine a a laser in in the optical uh sorry in the visible um wavelengths at around 532
Is a typical Ramen excitation laser if you if you shine that on the surface of say a coinage metal where you’ve got a lot of free electron density at the surface you basically excite plasmons in that surface and what that does is it enhances the local electri electric
Field just within the first so say 20 nanometers of that um of that surface and that has has a couple of useful effects first of all uh it massively increases the sensitivity of the rahen technique because basically one in every I think 10 billion photons is inelastically scattered so in normal
Ramen spectroscopy we’re we’re dealing with very very low odds if we can improve it by factors of up to 10 to the 10 which is numbers reported in the literature for enhancement factors then we’re we’re in a much better position that’s perhaps what’s the biggest strength of of surface enhanced rahen
Spectroscopy is in the name the fact that it’s localized to within the top 20 nanometers of the surface means only stuff that’s within that zone of your electrode will be detected so you can truly look at surface and interfacial phenomena this way um so how do we do
That well I mean there are lots of different ways of doing that spectral electrochemist Tech Al the easiest way is if your coinage metal that uh that you’re using for your s enhancement in this case gold if it happens to be catalytically active towards the reaction of Interest then that’s great
Because then you can just stick gold nanoparticles on on a surface and and do electrochemistry and the S enhancement will just tell you about that that that gold surface trouble is given that the particle size that we need for for S typically is in the order
Of 50 NM gold 50 animers is pretty much bulk gold um and so you’re not going to necessarily get a lot of um catalytic interesting cat catalysis going on at that scale you can also use silver and copper so there are other reactions of course of interest but that that creates
A limitation on what you can you can use the technique for so a way to sort of expand the range of of materials you can look at is to use this this technique on the right we it’s often called borrowed S effect where you where you basically coat your s particles with
Um uh uh the material of Interest so let’s say you coat it with a shell of platinum and then you can probe the catalysis that’s happening on the Platinum um and use the SES from the underlying gold um but again there are a lot of reasons why that might not be
Ideal first of all you’ve got to be able to deposit a very thin shell of of platinum or or your Catalyst onto the surface of the of the Sur particle also you don’t know whether the gold is is messing with your catalysis because if you’ve got a gold Platinum interface
That’s almost certainly going to be changing the electronic structure of that Platinum so you can’t really independently use this on its own so the real breakthrough was made uh 13 years ago in jamen who came up with this technique called shell isolated nanoparticle enhanced Ramen scattering and in this technique basically you take
A s nanop particle let say 50 nanometer gold or 20 nanometer gold uh particle and you coat it with very thin dialectric um such as uh silicon oxide or Al aluminium oxide what that does is it it it chemically isolates the The Sur particle from the environment that
You’re using to test um but it you still get a little bit of transmission of that enhanced electric field through that very thin dialectric shell so you can then basically sprink sprinkle this kind of magic dust onto your sample and uh and use it as a kind of universal
Enhancer for any system in principle and the the beauty is it can be used in conjunction particularly with single Crystal electrochemistry which is really good for uh detecting or for for understanding uh atomic structure function activity relationships and the like uh so just by putting these particles onto a single Crystal
Electrode we can we can learn an awful lot so uh to give you a case study of this again I don’t really have a lot of time to go into the detail but this was the the sort of reaction of interest it’s ethal perate which is an alpha keto
Eser um itself is used in in the fragrance industry but actually it was it was a particular interest because that that keto group is a is a is proyal so you can you can obviously get two an antimers out of this and there’s a lot of interest in in chyro chemistry we
Weren’t looking at anything chyal in this work uh but in principle you you you could uh so but we using this as our kind of model model system and what we’re showing you here on on the right hand side is the single Crystal electrochemistry of platum 11 one1 one 0
0 and one one0 um before and after we’ve basically dosed that surface with e this ethal perate molecule so that’s what you’re seeing in red and then the green traces are what’s happened after we’ve evolved hydrogen from the electrod surface and we’ve done that by applying
A negative or a bias close to zero volt so it’s enough to basically generate a hydrogenating environment and you can see the Platinum 111 is hardly affected but the Platinum the other two surfaces when you put the the ethy perate EP on the surface you massively change the um
The sort of absorption properties of the surface you basically block all of the Platinum sites which is as it reflected in in the sort of absence of all these features but what’s nice is after we do the the Platinum the hydrogen Evolution at the surface we basically get the
Original surface back so what’s happening there is the hydrogen the hydrogen that we’re generating at the Platinum is is is is is hydrogenating uh the uh the substrate that’s actually on your platinum surface and it’s and it’s being kicked off off so we were’re able to basically clean
Our electrode by by hydrogenation um so Gary atod and and and and co-workers have done a lot of work in that area um particularly using S but we wanted to in this work to look at uh shiners so this is some of the data that you can see
Here um and you can see there is clearly some structured dependence on on the spectrum that you get so the bands that I’ve labeled in green or highlighted in green the 490 and the 1050 um are basically they’ve been previously identified as this half hydrogenated state where basically you take one atom
Of hydrogen and put it on the the keto group of your uh of your ethal perate and the presence of that is clearly structure dependent in particular you notice Pure Platinum 111 clean Platinum 1111 doesn’t have any bands Associated that with that but as soon as you
Roughen it and by that I mean oxidize it so you introduce a load of defects uh you suddenly get that ban so that’s a really nice demonstration that that half hydrogenation state is particularly uh prominent in in in defective and stepped surfaces but we also saw in our in our
Sher’s data these additional bands 418 and 965 we had no idea what they were what they were about um we noticed that they they changed with potential so there is a potential dependence of that uh of those B of those bands but the point is they were they were pre
Prevalent at high potential so it’s not to do with hydrogen this probably to do with some kind of absorbed species in the presence of uh of this ethal perate so we turned to some colleagues David willick at uh Cardiff did did some DFT modeling um for us and basically came up
With the best guess as to what might be the source of these bands and and that was this uh meww absorb baate and what we believe that to be is basically a precursor to the half hydrogenated State um and if you look at the the absorption
Energies of this this precursor on a on a clean Platinum 111 Surface versus a stepped uh surface you can see there’s there’s a big difference in that absorption energy whereas the half hydrogenated States the HHS have similar kind of binding energies uh for the for the two systems the precursor has has
Has quite different energetics and so that’s a possible reason why stepped surfaces are uh we find a lot of this half hydrogenated State basically it’s a potential well so basically it’s very very stable on those on those defective sites and almost doesn’t want to come out again whereas in the case of the
Platinum 111 it must it must enjoy being in the in the in the precursor State a little bit more um so that was quite an interesting uh sort of example of of how we could learn a little bit about what’s happening at the surface prior to in this case a hydrogenation
Reaction uh and then more recently sha Lang has also published some more work from his PhD looking at uh Al P hydrogenation again a structure sensitive process um and uh and this in this case it’s the reaction is sensitive to the substituents that you have attached to your Al alkine group I’m not
Going to go into into this one at all but feel free to ask at the end or or we can uh the work has has been published as well and also very very recently um my some other colleagues of mine at at uh Strath Clyde University have looked at an alternative
Coating method for these shiners particles again I haven’t got time to go into the details but rather than using a dialectric um of of uh like alumin alumina or silica you can use polymeric species um so there are there are ways forward for that that technique so
Finally I just want to touch upon some work uh we’ve been do it’s actually some quite old work actually uh but we’re still Keen to push the technique a little bit more uh on on tip enhanced Ramen spectroscopy be so the problem with the techniques that I’ve talked about so far is you’re
Basically defraction limited so the best spatial resolution you can really hope for is Micron scale maybe submicron if you’re really really careful um what we’d obviously like to do is be able to do spatial spatially resolved spectroscopy at the at the kind of nanometer scale and tip enhanc Ramen is
Is is a way to do that so what we can do is basically do serves at the very Apex of a in this case AFM tip or you can use a STM so um scanning um uh yeah sorry STM tips um basically it doesn’t really matter how you control
The the feedback and and how close your tip is to the sample really all it is is being able to bring that a plasmonically active uh Apex close to your sample so what you do is you use in this case AFM to um uh uh to basically contact your your your sample surface
And you excite that plasmon at the very very Apex and and so you can get spatial resolution that is defined by your geometry of your tip which could be in the tens of nanometers I’ve seen reports of of of nanometer scale resolution um but of course it’s it’s quite
Challenging as you as you can imagine uh in this case we use some um a photocatalytic reaction rather than an electrochemical one um just because it’s a little bit easier uh we use this this model reaction where you use aminophenol ATP and you you you can use oxidative coupling of that to
Form the the AO Benzene and the beauty of that reaction is that the the AO groups light up quite nicely in ramen so you can you can track the reaction quite nicely using Ramen spectroscopy and that is catalyzed on on on Silver but but other other surfaces as well um the
Problem with it being catalyzed on Silver is that we’re using silver as our probe so we showed actually that just by touching a a a clean probe to an a 480p surface we could actually see reactivity at that Apex U which is a nice sort of interesting observation but it means we
Can’t independently study catalysis if our probe is catalytically active um so what we did was we took sort of a leaf out of the shiner’s uh book which is to coat our catalytically act or plasmonically acve um tip with with alumina in this case so just a couple of
Nanometers of alumina enough to chemically block the uh the catalysis but we still get the the electronic um electric field enhancement that gives us the S effect and we see quite clearly that we don’t we don’t get any any chemical reactivity so we’ve managed to chemically sort of isolate that and then
We applied this to a a kind of patterned surface it didn’t work as well as we’d like but what we did was we patterned a surface a glass surface with with bits of silver and then uh like pockets of silver and then we uh modified that silver with with this ATP molecule and
Then we did some some turs mapping and as you can see from the maps in the bottom left you’ve got different hotpots of reactivity um and and and the Spectra show that some regions have done the full reaction to the the dmab molecule and some regions haven’t so we are
Basically looking at different reactivity levels across the surface um something more recently was done with ber reisen’s group uh in utre again as part of a collaborative PhD student ship uh where we developed an alternative Coating in this case using zerconia to prevent the uh the silver of
Your AFM probe from uh getting in the way um and in this case it was used in a in a liquid droplet just to show that in principle that we’re moving step forward even if it’s just a tiny step at a time towards actual reactive chemistry and
Again we’re able to show that the surface has different regions of reactivity um uh corresponding to presumably structural variations or Atomic structural variations across the across the sample and then really finally um I we’ve sort of extended this tip enhanced Ramen spectroscopy to tip enhanced fluoresence microscopy so normally when
You’re doing Ramen spectroscopy fluoresence is a real pain um because it usually gives you very Broad baselines and and it really gets in the way but but fluoresence microscopy itself is actually quite a useful technique and Bert back kaisen group have shown that you can use this thiophene reaction to
Basically stain the acidic sites in zeolites um for for FCC type catalysis um and basically use fluoresence microscopy to detect where those uh those stain that that staining molecule has basically formed this um poly polymeric floresent species um the the challenge with normal fluoresence microscopy is it’s again typically uh um
Diffusion sorry defraction limited uh so you can’t get the best spatial resolution although there are examples of fluorescence microscopy beyond that um but this is quite a nice example of actually being able to do foressence microscopy at the very end of an AFM tip and again sort of circumventing the
Defraction limit and getting sort of 100 maybe 50 nanometer resolution uh out of that measurement so again it was really a proof of concept and you really got to go you really got to have the right system and the right chemistry to be able to probe it but but it is a step
Forward and and quite nice to be able to do that with such high spatial resolution uh so just to kind of bring it all together I think I hope I’ve demonstrated to the value of using vibrational spectroscopy to study interfacial systems as I said earlier I think confocal and ATR based methods are
Valuable to look at the actual electrodes themselves but if you want to look at the interface you’ve really got to make use of these surface enhancement effects so the turs and the shiners are really I think there’s a lot to be done in that area in terms of uh in the
Catalysis kind of Arena and ultimately they should be able to provide us with the the structure performance relationships that we ultimately crave um so just to wrap up um lots of people contributed to the work of over the years I mentioned sh Lang but and I W I
Won’t name any other names but we’ve we’ve had a number of collaborations and a number of funding agencies so I’ll I’ll leave that up there and and stop and thank you for your attention a few questions I’ve got a question I was wondering you co abortion o studies uh
Have you um managed to absorve the CO2 product and does it you know correlate with acation very good question um we did try um one of the problems with CO2 is this always CO2 everywhere um and our although we try to we do try and Purge our system with with
With nitrogen um you can’t it’s I think unless you use a vacuum system it’s very difficult to get a very good CO2 Purge so we did see variations in the CO2 signal but they’re almost certainly from external variations and it’s just very very challenging to do so I we we hoped
To do it but unfortunately weren’t successful but thank you good question hi nice talk I was just wondering if you could use temperature um to help you say with the fluoresence issue you have with the resolution you can use fles to your advantage and then maybe sort of call it down
So yeah I think that’s that’s idea I I think that would be that would be good for an exit you technique I think where our interest lies are for like looking at reactive systems and when you drop the temperature you you stop the reaction but that actually might be a
Good way to modulate the system so turn the reaction on and off and yeah that’s a nice nice trigger to have for sure the last question you had sort of a throwaway line okay you said that you would you didn’t get the the tster system you didn’t get the
300 you already got 100 is that because the others were measur in prop uh I hesitate to to say whether or not they didn’t measure it correctly the the the problem is the these things are very very sensitive to how you’ve made the material we not we weren’t studying exactly the same
Catalyst well yes so the error bar is is is huge um I dare say it was probably just a slightly different Catalyst um or they or they were reporting their very best results and we reported a nice an error bar on ours I think you’re second probably probably true probably it’s just interesting
Reprod well that’s that’s nl’s kind of territory yeah so Aly thank you very much okay