Efficient H₂ Evolution Coupled with Oxidative Refining of Alcohols via A Hierarchically Porous Nickel Bifunctional Electrocatalyst

Abstract

Water electrolysis to produce H2 and O2 with renewable energy input has been generally viewed as an attractive route to meet future global energy demands. However, the sluggish O2 evolution reaction usually requires high overpotential and may yield reactive oxygen species (ROS) that can degrade the electrolyzer membrane and hence shorten the device lifetime. In addition, the potential gas crossover may result in an explosive H2/O2 mixture and hence safety risks. To address these issues, we herein report a general electrolysis strategy for the simultaneous H2 production and alcohol oxidative upgrading (e.g., benzyl alcohol, 4-nitrobenzyl alcohol, 4-methylbenzyl alcohol, ethanol, and 5-hydroxymethylfurfural), in which the thermodynamics of the latter is much easier than that of water oxidation. A facile and environmentally friendly template-free electrodeposition was used to obtain a 3D hierarchically porous nickel-based electrocatalyst (hp-Ni) for such an integrated electrolysis, requiring a voltage of ∼220 mV smaller than that of water splitting to achieve 50 mA cm–2 together with robust stability, high Faradaic efficiencies, and no formation of ROS, as well as production of valuable products at both the cathode (H2) and anode (alcohol oxidation products). More importantly, we demonstrated that these diverse alcohol oxidations over hp-Ni exhibited similar onset potentials which were largely determined by the desirable oxidation potential of hp-Ni, irrespective of the different intrinsic thermodynamics of these alcohol oxidation reactions. This result provides a new direction for the rational design of heterogeneous transition-metal-based electrocatalysts with lower oxidation potential for more highly efficient electrocatalytic alcohol oxidation.