The development of highly active and stable non-noble metal oxide catalysts to replace iridium-based materials for efficient acidic water electrolysis is crucial1–3. However, traditional spinel cobalt oxide suffers from intrinsic performance limitations from coexistence of inactive tetrahedral (Td) and highly active octahedral (Oh) coordination sites4,5. Here we report a new trigonal-phase Co3O4 (Tri-Co3O4) produced by a vacuum-mediated molten-alkali mechanochemical method, which shows edge-shared [CoO6] octahedral coordination with the space group P-3m1 (164). The three-layer compact structure provides Co2+ and Co3+ located in octahedral coordination in the ratio 1:2. Tri-Co3O4 achieves a low overpotential of 269 millivolts (mV) at the current density of 10 mA cm−2 in the acidic oxygen evolution reaction (OER), 181 mV less than spinel-type Co3O4. It also achieves a current density exceeding 1,800 mA cm−2 at a cell voltage of 1.80 V in proton-exchange membrane water electrolysis (PEMWE) devices. The catalytic mechanism shows that the 2D layered structure with edge-shared octahedral coordination can effectively optimize the adsorption of intermediates and reduce the dissolution of Co, thereby substantially improving the activity and stability of the non-noble metal catalysts.
