Understanding N-doped graphene electrocatalysts through in-situ characterisation

In battery technology, a good understanding of what goes on at the interface between the solid electrodes and the liquid electrolyte is critical. As a battery charges and discharges, electrochemical reactions occur at the electrodes, some desirable, some undesirable. Understanding these reactions and how to promote the desirable ones and eliminate the undesirable ones holds the key to making better batteries.

The challenge to scientists is that working out what is going on at the electrode/electrolyte interface is very difficult as in a working battery, this interface is hard to get to - buried by the electrode on one side and the electrolyte on the other. Traditionally we relied on post mortem measurements - ie. dismantling the battery, and looking at the electrode surfaces after operation. There are two problems with this, firstly that the removing the electrode will most likely change its composition (eg. by oxidation). The second, and more serious, problem is that these measurements only tell you what is happening after an electrochemical reaction, not during. The state of the surface during reaction is critical to understanding it, so there is a strong push to develop operando measurement techniques (ones that can take measurements during electrochemical processes).

X-Ray Photoelectron Spectroscopy (XPS) is an analytical technique which provides chemical information about the surface of a sample. It works by firing X-rays at a sample and detecting the electrons emitted in response. These electrons carry with them information about the surface atoms they have come from. It's the most versatile and powerful probe of surface chemistry and has been in use in battery research for many years. It is, however, a post-mortem technique, requiring high vacuum conditions to operate.

Developing XPS such that it can study electrochemical reactions in-situ is very technically challenging but potentially very rewarding - the ability to study electrochemical interfaces in-situ could be revolutionary. There is intense activity in this area and several competing approaches which place stringent restrictions on sample geometry or require complex sample fabrication.
I am leading research in Manchester to develop a new approach to electrochemical XPS. Our approach is uniquely versatile and can be applied to practically any sample. Our approach involves projecting a small droplet of electrolyte onto the sample surface inside our XPS instrument and creates an electrochemical cell with that droplet. We can then study the edges of the droplet using XPS, where the liquid layer is thin enough that we can detect electrons from the electrode/electrolyte interface. We have recently published proof-of-concept results showing characterisation of this interface.

The purpose of this proposal is to build on this development and to extend the electrochemical XPS technique so that is a reliable and useful research tool.

We will then apply this tool to gain insight to an electrochemical problem relevant to emergent battery technology. Nitrogen - doped graphene (Graphene with some of the carbon atoms swapped for nitrogen) has been shown to be an excellent electrocatalyst for the oxygen reduction reaction (ORR). This reaction is a key bottleneck in the development of air battery technology, a promising emergent battery technology which has the potential to deliver batteries with 10 times the capacity for the same weight. However, development of N-graphene electrocatalysts is hampered by a very poor understanding of how they work. Electrochemical XPS will allow us to follow the surface chemistry of these catalysts whilst they are operating and therefore gain unprecendented insight into how they work.

I propose to develop a novel and uniquely versatile approach to operando electrochemical characterisation using XPS. This enables the study of operando surface chemistry which has potential beneficiaries across a range of sectors, outlined below.

Battery/automotive industry: The ability to study the operando surface chemistry of battery electrodes is potentially transformative as the fundamental understanding of electrode processes gained could enable significant advances in battery technology based on rational design. This is particularly timely as hugely improved batteries are a key priority for the transformation of the transport sector to electric vehicles. There is intense research within both industry and academia to understand and improve battery technology and the developments proposed here will benefit both.

Other industrial processes: Electrochemistry is fundamental in a wide range of industrially important processes, and the capability to study these processes in operando has the potential to deliver huge leaps in understanding. Examples include electroplating (coatings industry), corrosion protection (many corrosion processes are electrochemical in nature), refining of metals and the manufacture of chemicals.

2D materials: Research into 2-D materials is now a research field in its own right and 2D materials are being investigated for a variety of applications beyond energy, eg. electronics, inks, composites, sensors and many more. The ability to controllably "dope" 2D materials with heteroatoms to and understanding the chemical reactivity of these heteroatoms will surely find application in many of these fields, modifying the properties to increase their usefulness for a particular application. A significant proportion of this project will be devoted to understanding how to incorporate nitrogen into graphene and investigating in detail the inequivalent dopant sites and their properties. The fundamental understanding we will gain will be taken up by more applied researchers looking to employ 2D materials in a variety of applications and to industries looking to exploit the unique properties of 2D materials in their products.

UK characterisation capability: A key strength of UK science and technology is cutting-edge materials characterisation facilities such as the Henry Royce Institute and the Diamond synchrotron. The proposed developments in this proposal would generate a world-unique characterisation capability, available through both of the above facilities. This was aid these facilities in retaining their world-leading status and attracting new international collaborators.

General public: A key part of this proposal is to engage with the general public and provide accessible, educational resources about our research and battery technology in general, primarily online.