Ultra-low loading Pt electrocatalysts based on carbon support alloys for oxygen reduction in hydrogen fuel cells and their lifetime prediction

The oxygen reduction reaction (ORR) on the cathode is a core electrochemical process in fuel cells. A four-electron transfer ORR is favourable, which involves the cleavage of O=O bonds and the formation of OH* or OOH* species. The reaction kinetics tend to be sluggish, and normally require high overpotentials which significantly affect the energy conversion efficiency. The benchmark electrocatalysts for four-electron transfer ORR overwhelmingly rely on noble metal materials owing to their excellent catalytic activities, i.e. 20~40 % platinum (Pt) on carbon materials for cathodes in fuel cells. However, the high cost and durability issues of Pt materials hinder their large-scale application. In addition, the current evaluation of ORR catalysts needs the long-term stability test and materials stability analysis, which occupy a large amount of the effort and time. Developing suitable programme for lifetime prediction of the electrocatalysts and fuel cells are important for further reducing the device cost.

This project aims at developing low-cost and sustainable materials, frameworks and the project is divided into three stages:

Stage 1) Materials preparation: The bottom-up strategy will be used to prepare the modified carbon materials via combined wet chemistry and solid-state annealing processes. The mixture of a single-carbon precursor, including tannic acid, glucose, potato starch and polyethylene glycol (these precursors have rich oxygen functional groups and will form cross-linking products and oxygen functionalised structure initially. Different transition metal salts (Co, Fe, Ni, etc.) and reduced amount of the Pt precursor will be involved. After annealing under a reductive atmosphere, the alloy clusters will be formed on the porous carbon supports. Furthermore, non-metal atoms will be involved to further optimise the electronic conductivity and the interaction among alloys and carbon supports, such as the nitrogen or phosphorus into the frameworks. The uniformity, phases and structures of the materials can be adjusted systematically. A broad range of materials characterisation techniques will be adopted, such as scanning (transmission) electron microscopy, X-ray diffraction and BET surface area evaluation.

Stage 2) Electrochemical evaluation and fuel cells fabrication The ORR performance will be tested in a three-electrode configuration. The working electrode will be prepared by coating electrocatalyst mixtures onto a rotating disk electrode (RDE, glassy carbon disk) or a rotating ring disk electrode (RRDE, glassy carbon disk with Au/Pt ring). Kinetic behaviours and the stability of as-prepared electrocatalysts will be evaluated and compared with the commercial Pt/C materials. Electrochemical impedance spectroscopy will be used to understand the inherent resistance. The fuel cell fabrication and testing will be conducted via the collaboration with Bramble Energy ltd. and DB's group.

Stage 3) Mechanism study and lifetime estimation The student will work with SJ and GH's group to understand the mechanism of electrocatalysts and develop suitable machine learning algorithms to predict the lifetime of the electrocatalysts according to the initial evaluation of the electrochemical performance. In-situ spectroscopic and tomography study, such as in-situ electrochemical Raman spectroscopy from the School of Chemistry will be used further guide the development of new materials.