Nanocrystalline Ni 5 P 4 : a hydrogen evolution electrocatalyst of exceptional efficiency in both alkaline and acidic media

Producing hydrogen (H 2 ) by splitting water with fossil-free electricity is considered a grand challenge for developing sustainable energy systems and a carbon dioxide free source of renewable H 2 . Renewable H 2 may be produced from water by electrolysis with either low efficiency alkaline electrolyzers that suffer 50–65% losses, or by more efficient acidic electrolyzers with rare platinum group metal catalysts (Pt). Consequently, research has focused on developing alternative, cheap, and robust catalysts made from earth-abundant elements. Here, we show that crystalline Ni 5 P 4 evolves H 2 with geometric electrical to chemical conversion efficiency on par with Pt in strong acid (33 mV dec −1 Tafel slope and −62 mV overpotential at −100 mA cm −2 in 1 M H 2 SO 4 ). The conductivity of Ni 5 P 4 microparticles is sufficient to allow fabrication of electrodes without conducting binders by pressing pellets. Significantly, no catalyst degradation is seen in short term studies at current densities of −10 mA cm −2 , equivalent to ∼10% solar photoelectrical conversion efficiency. The realization of a noble metal-free catalyst performing on par with Pt in both strong acid and base offers a key step towards industrially relevant electrolyzers competing with conventional H 2 sources.