An efficient NiCoSe4/NiCo-LDH/CF catalyst for the co-production of value-added formate and hydrogen via selective methanol electro-oxidation

Abstract

The sluggish kinetics of the anodic oxygen evolution reaction (OER) and the valueless product O₂ are tricky issues for water splitting. Replacing the OER with a more thermodynamically favorable selective methanol oxidation reaction (SMOR) to combine with the hydrogen evolution reaction can not only lower the applied voltage but also simultaneously produce value-added formate in the anode and hydrogen energy in the cathode. Herein, a mirror-like heterostructure of NiCoSe₄@NiCo-LDH supported on cobalt foam (NCS/CF) was synthesized by partial selenidation of NiCo-LDH to facilitate the SMOR. Experimental tests and theoretical calculations revealed the “shuttle-like” role of Se in NCS/CF, by which electrons of Ni were first transferred to Se and then to Co. Moreover, the superiority of the bimetallic compound was also proved by comparing the activity of NCS/CF to that of the counterparts NiSe₂@Ni(OH)₂/CF (NS/CF) and CoSe₂@Ni(OH)₂/CF (CS/CF). Owing to the unique electronic effect of the strongly coupled hetero-interface and the bimetallic synergism, more accessible active sites, fast charge transfer ability, facilitated catalytic kinetics, and modulated electron redistribution were achieved. Therefore, improved SMOR performance was obtained with ∼100% faradaic efficiency of methanol-to-formate. The potential at 10 and 100 mA cm⁻² was only 1.274 and 1.432 V vs. RHE, respectively, outperforming most existing catalysts. In addition, the two-electrode electrolyzer of methanol-assisted water electrolysis with NCS/CF as both the anode and cathode only required an applied cell voltage of 1.380 V to reach 10 mA cm⁻², 253 mV less than that of pure water splitting. Meanwhile, outstanding catalytic stability was achieved by continuously delivering a current density of 100 mA cm⁻² for 100 hours without obvious attenuation. The inference of the “shuttle-like” role of Se will provide new insight into the electronic redistribution in the NiCo-LDH derivative that is incorporated with foreign atoms. The integration of methanol upgradation and hydrogen generation exploits an energy-saving way to simultaneously obtain value-added organic substances and green hydrogen.