In Situ\nElectrochemical Oxidation Synthesis of SyA-Cu/CuO/NF\nHeterostructure As Trifunctional Electrocatalyst for UOR, BOR, and\nHER at Industrial-Scale High Current Density

The construction of bifunctional or trifunctional electrocatalysts\nwith excellent performance for highly effective overall water splitting\nis highly desirable and extremely challenging. Herein, Cu-based metal–organic\nframeworks (MOFs) nanomaterials using syringic acid (SyA) as ligands\nare grown on nickel foam (NF) by a one-step solvothermal method, namely,\nthe self-supported precursor (SyA-Cu/NF); further, a SyA-Cu/CuO/NF\nheterostructure is obtained by in situ electrochemical oxidation of\nthese precursors, which is applied to the urea oxidation reaction\n(UOR) and benzyl alcohol oxidation reaction (BOR). The optimal SyA-Cu/CuO/NF\nheterostructure could reach 100 mA cm<sup>–2</sup> on only\napplying 1.47 V (vs RHE) with a Tafel slope of 53 mV dec<sup>–1</sup> for UOR and 1.44 V with a Tafel slope of 32 mV dec<sup>–1</sup> for BOR. Furthermore, it also displays hydrogen evolution reaction\n(HER) activity, showing a low overpotential of 92 mV at 10 mA cm<sup>–2</sup>. Above all, coupling UOR and BOR, it is used as a\nbifunctional electrocatalyst for the overall water splitting, which\ncan reach 10 mA cm<sup>–2</sup> at 1.47 and 1.45 V, respectively.\nTherefore, this SyA-Cu/CuO/NF heterostructure is a potential trifunctional\nelectrocatalyst for UOR, BOR, and HER due to its unique interface\ninteraction between SyA-Cu/CuO and the intermediates/electrolyte.