Superstructures of Organic-Polyoxometalate co-Crystals as Precursors for Hydrogen Evolution Electrocatalysts

The scalable production of hydrogen through water electrolysis is recognized as a green and sustainable pathway for a future energy supply. Benefiting from similar electronic properties as Pt-group metals, molybdenum (Mo)-based carbides and nitrides have been considered as promising catalysts for the hydrogen evolution reaction (HER). Currently, one of the substantial challenges using Mo-based HER electrocatalysts lies in establishing well-defined precursors which can be transformed into Mo-based carbides/nitrides with controllable structure and porosity. Here we report the synthesis of a series of superstructures consisting of organic-polyoxometalate co-crystals (O-POCs) as a new type of metal-organic precursor to synthesize Mo-based carbides/nitrides in a highly controlled fashion and to use them for efficient catalytic hydrogen production. This protocol enables to create electrocatalysts composed of abundant nanocrystallites and heterojunctions with tunable micro- and nanostructure and mesoporosity. The best performing electrocatalyst shows high HER activity and stability with a low overpotential of 162 mV at 100 mA/cm 2 (in comparison to Pt/C with 263 mV), which makes it to one of the best non-noble metal HER catalysts in alkaline media and seawater.