Surface reconstruction of phosphorus-doped cobalt molybdate microarrays in electrochemical water splitting

P-doped CoMoO 4 (P-CoMoO 4 ) vertical microarrays, underwent surface reconstruction during the electrochemical processes, are highly efficient for electrocatalytic hydrogen and oxygen evolution. • Construction of P-doped cobalt molybdate (P-CMO) microarrays with controllable crystallinity. • Highly efficient alkaline water splitting performances from the optimized P-CMO catalyst. • Careful investigation of the surface reconstruction during the HER and OER processes. It is highly desired but still challenging to develop highly efficient catalysts for electrochemical water splitting. Herein, we report the fabrication of phosphorus-doped monoclinic β -CoMoO 4 (P-CoMoO 4 ) on nickel foam as a high-efficiency and bifunctional electrocatalyst for overall water splitting in alkaline electrolyte. Surface reconstruction of P-CoMoO 4 is witnessed and carefully investigated, which is converted into Co(OH) 2 -CoMoO 4 /P-CoMoO 4 during the hydrogen evolution reaction (HER) process, and into CoOOH/P-CoMoO 4 during the oxygen evolution reaction (OER) process. Notably, the reconstructed catalyst exhibits ultralow overpotentials of 44 mV to achieve a current density of 10 mA cm −2 for HER, and 260 mV to deliver a current density of 20 mA cm −2 for OER. Meanwhile, it only needs a small cell voltage of 1.54 V at 10 mA cm −2 for robust water splitting with outstanding long-term durability over 72 h at 50 mA cm −2 . This study reveals the significance of surface reconstruction of transition metal oxides for highly efficient water electrolysis.