In the second of a CARES C4T series of short articles focusing on the potential real world impact of the programme’s research, Yuan SHENG (Project Officer, IRP3, NTU), explores the benefits of developing flame synthesis methods to prepare low-cost, high-performance catalysts for water splitting.

Hydrogen is a major feedstock for the chemical industry and consumed in large scales by heavy oil hydrocracking, ammonia and methanol syntheses processes. Today it is produced almost exclusively from fossil fuels, accompanied by enormous CO2 emission. If hydrogen from renewable sources, for example, solar-powered water splitting, were to feed the chemical processes, dramatic reduction in carbon footprint is then expected. Unfortunately high price of the “green hydrogen” has prevented its commercial success so far, but there do seem to be chances to change the situation, fortunately.

Some of the most important problems in the electrolytic production of green hydrogen are inefficient electricity-to-hydrogen conversion, high capital cost and poor durability of electrocatalysts. To overcome the activation barrier of the electrolysis reaction, an extra voltage beyond thermodynamic requirements, or overpotential, needs to be applied for any meaningful rate of water splitting. State-of-the-art precious metal catalysts including Pt, RuO2 and IrO2 can lower the overpotential to ~0.4 V, which still translates into at least 25% loss of energy as heat. With fast advance in nanotechnology, non-precious nanocatalysts achieving even better performance have been developed in research labs. However, largely wet-chemistry-based syntheses of the nanocatalysts are lengthy and costly, producing significant amount of hazardous waste at the same time. In addition, stability issues of the catalysts remain unresolved.

In CARES C4T, we are developing flame synthesis methods to prepare low-cost, high-performance catalysts for water splitting. During flame synthesis, vapours of precursors for the catalysts are introduced to a burning flame (H2/O2 for example) where catalyst nanoparticles form. Advantages of this method are 1) fast speed, 2) almost 100% yield from catalyst precursors, 3) negligible waste production, 4) ability to coat catalyst in situ on various substrates to prepare ready-to-use electrodes, 5) possibility of synthesizing different materials using the same process, and 6) suitability for continuous, large-scale production. It is hence expected to significantly reduce production as well as R&D costs of water splitting electrodes, which may ultimately lead the green hydrogen technology to commercialization.

Applications of the flame synthesis method are not limited to preparing water splitting catalysts. Since composition and morphology of flame-synthesized particles/films can be conveniently tuned, other low-carbon-footprint technologies such as photovoltaics, electrochemical CO2 utilization and fuel cells may also benefit from these low-cost electrodes. In the end, combustion, which most people will consider as the very source of CO2 emission, could actually help realize a carbon-neutral industry.

Yuan SHENG obtained B.Eng (1 st Hons.) in Chemical Engineering at the National University of Singapore and continued with PhD study supported by the President’s Graduate Fellowship in the same university. His thesis is on synthesis of hierarchically porous nanocatalysts for CO 2 utilisation. He has recently joined CARES C4T as a Project Officer in IRP3.

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