Crystal phase tuning and valence engineering in non-noble catalysts for outstanding overall water splitting†
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/Ni0.46Co0.54 hybrid catalyst with an open 3D nanostructure is constructed using electrochemical co-deposition to fabricate the Ni0.46Co0.54 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 Ni0.46Co0.54 alloy offers abundant active sites for the highly efficient OER. Moreover, the optimized Ni0.46Co0.54 alloy works synergistically with CoNiO2 to further boost the intrinsic HER performances. The resulting CoNiO2/Ni0.46Co0.54 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.