Crystal phase tuning and valence engineering in non-noble catalysts for outstanding overall water splitting

Abstract

Designing high-efficiency non-noble electrocatalysts with a bifunctional feature for the durable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is desirable for large-scale hydrogen generation. Here, a self-supported CoNiO₂/Ni_0.46Co_0.54 hybrid catalyst with an open 3D nanostructure is constructed using electrochemical co-deposition to fabricate the Ni_0.46Co_0.54 parent alloy followed by a one-step annealing process. This self-supported 3D nanostructure derived by tuning the crystal phase of the parent alloy provides a large surface area and barrier-free electron transport medium. The CoNiO₂ with a high ratio of Ni³⁺ and Co²⁺ converted from the surface layer of the Ni_0.46Co_0.54 alloy offers abundant active sites for the highly efficient OER. Moreover, the optimized Ni_0.46Co_0.54 alloy works synergistically with CoNiO₂ to further boost the intrinsic HER performances. The resulting CoNiO₂/Ni_0.46Co_0.54 hybrid catalyst exhibits superior activity with 58 and 195 mV to achieve a current density of 10 mA cm⁻² for the HER and OER, respectively. Moreover, it requires a quite small cell voltage of 1.51 V to drive 10 mA cm⁻² for overall water splitting and outperforms all the reported catalysts. Impressively, it shows excellent durability at a commercially practical current of 500 mA cm⁻² for 30 h, suggesting promising applications for large-scale hydrogen generation.