High Performance Non-Noble-Metal Based Catalysts for Water and Seawater Electrolysis
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Water and seawater electrolysis to produce high caloric hydrogen gas is a sustainable and environmentally friendly energy-conversion technology that can be used to decrease the excessive consumption of fossil fuels. In general, water electrolysis is composed of two half reactions: oxygen evolution reaction (OER) on the anode and hydrogen evolution reaction (HER) on the cathode. To make electrolysis process energy-efficient and cost-effective, catalysts, which can promote the sluggish kinetics of OER or HER by lowering their activation energy, are extensively studied. However, conventional noble-metal based catalysts such as Pt-/Ir-/Ru- composites suffer from high cost and scarce availability despite their high catalytic activity. Developing alternative non-noble-metal based catalysts with high catalytic activity and long-term durability is desirable but remains a challenge. At the same time, seawater electrolysis is attracting growing research attention due to its obvious advantages such as inexhaustible resource reserves, easy combination with ocean-related renewable-energy technologies and by-production of freshwater. However, the complicated composition of natural seawater can result in additional challenges for direct seawater electrolysis including competing chlorine evolution reaction, chloride corrosion, and catalyst poisoning. Addressing these challenges requires rational design of catalysts dedicated to seawater electrolysis. Here we apply various synthetic approaches to synthesize efficient non-noble-metal based catalysts for large-current-density water and seawater electrolysis, including tungsten-doped nickel iron layered double hydroxides (Ni-Fe-W LDH), boron-modified cobalt iron layered double hydroxides (B-Co2Fe LDH), and core-shell-structured CoPx@FeOOH for OER, heterogeneous metallic nickel and molybdenum nitride (Ni-MoN) for HER, and bimetallic phosphide (Ni2P-Fe2P) for both OER and HER. Rational design enables these novel catalysts to exhibit high catalytic activity, long-term durability, and enhanced chemical/structural stability to work well in both alkaline freshwater and seawater electrolytes. In these specific works, the effects of elemental doping, structural tuning, crystallinity adjustment, phase combination, electronic structure optimization, surface properties, corrosion resistance, and many other conditions on catalytic performance are investigated. Theoretical calculations are attempted to investigate the active sites and physical and chemical characterizations before and after catalytic reactions are conducted to reveal the transformation of these catalysts during electrolysis process.