In-situ studies of electrocatalysts using Near-Ambient Pressure

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Current fuel cell technology requires the use of large amounts of platinum as an electrocatalyst. This is the major barrier to the widespread adoption of fuel cells - there simply isn't enough platinum in the world. It is therefore critical to find replacement catalysts made of earth-abundant elements. Graphene doped with Nitrogen (N-graphene) has recently been shown to show great promise as an electrocatalyst for the Oxygen Reduction Reaction (ORR). However the chemical nature and location of the active sites (N dopants occupy several inequivalent sites on the graphene lattice) are still under debate and the reaction mechanism is completely unknown. This project will develop a new in-situ technique which will allow us to follow the surface chemsitry at the electrode/electrolyte interface of N-graphene electrocatalysts during operation. X-Ray photoelectron Spectroscopy (XPS) is a powerful probe of surface chemistry. X-Rays are fired at a sample and the resulting photoelectrons detected. Their energy is characteristic of the elements present and their chemical environment. It is surface sensitive, as only electrons generated near the surface escape and are detected. Studying the electrode/electrolyte interface in-situ using XPS is challenging for two reasons. Firstly, this interface is buried by electrode on one side and electrolyte on the other. Secondly, XPS is a high vacuum technique, so samples containing a liquid electrolyte cannot be studied. This project will make use of cutting-edge instrumentation available at Manchester, Near-Ambient Pressure XPS (NAP-XPS). This new instrument can study samples in high pressures, allowing the study of samples containing liquid water. By using a single layer of graphene as an electrode, photoelectrons can escape through the electrode and be detected. This will allow us to study the electrode/electrolyte interface while the catalyst is in operation. The project will consist of three parts: Control and optimise the growth of N-doped graphene. Using Chemical Vapour Deposition (CVD), you will grow single-layer graphene doped with N atoms. Using a combination of XPS and atom-resolved microscopy, you will investigate how growth conditions affect the N dopant concentration and type. Develop and optimise the in-situ electrochemical cell. Our group has developed an in-situ electrochemical cell based on an ultathin graphene membrane. Proof-of principle has been demonstrated but significant optimisiation is required to make it a viable research tool. Working with other group members and collaborators, you will help optimise this system using N-graphene as a test system. Measure the ORR in-situ. By monitoring the chemical state of the N dopants during the ORR, we will learn about intermediate species, gain insight into the reaction mechanism and poisoning/deactivation mechanisms. By using the insight gained from this and the control over graphene doping learned in part 1, we can then optimise our N-graphene for maximum catalytic performance.