Water splitting driven by renewable energy could be used to provide hydrogen as a clean, sustainable fuel. Water splitting requires efficient catalysts for both the hydrogen and oxygen evolution reactions (HER and OER, respectively). Low-cost, efficient bifunctional catalysts for overall water splitting would be particularly useful.

Jian-Bo He, Hefei University of Technology, China, and colleagues have synthesized a bifunctional Ni-Fe-S electrocatalyst for both the hydrogen and oxygen evolution reactions in 1.0 M KOH. The team used intergranular defects or nanopores inside polycrystalline graphite as nanoreactors for the in-situ synthesis of the catalyst (pictured schematically). They used two precursor solutions, which can penetrate the intergranular nanopores in graphite to a depth of more than 3.5 mm and then form the catalytically active species. The researchers used solutions of thioacetamide (CH₃CSNH₂) as sulfur sources together with mixed precursor solutions of Ni(NO₃)₂ and Fe(NO₃)₃. These solutions were drop-cast onto graphite to obtain the desired nickel and iron (di-)sulfide (Ni-Fe-S) composite nanoparticles.

The graphite substrate provides a rigid conductive medium which lowers the electron transfer barrier between the catalyst particles and improves their stability. The resulting catalyst shows excellent catalytic activity and long-term stability at a high current density of 400 mA cm^–2. The synthesis strategy based on using the nanopores inside a monolithic conductive substrate could provide a simple and efficient method for the preparation of electrocatalysts.

• High-performance bifunctional Ni-Fe-S catalyst in situ synthesized within graphite intergranular nanopores for overall water splitting,
  Xiao-fan Yang, Jing Li, Xin-ming Yang, Chao-xiong Li, Fang Li, Bing Li, Jian-Bo He,
  ChemSusChem 2021.
  https://doi.org/10.1002/cssc.202100891