Ultrathin Metal-Organic Framework Nanosheets-Derived Yolk-Shell Ni0.85Se@NC with Rich Se-Vacancies for Enhanced Water Electrolysis

We present a controlled fabrication of selective ultrathin metal-organic framework (MOF) nanosheets as preassembling platforms, yolk-shell structured with a few-layered N-doped carbon (NC) shell-encapsulated Ni0.85Se core (denoted as Ni0.85Se@NC) via an oriented phase modulation (OPM) strategy. The ultrathin nature of the MOF nanosheets gave rise to the modification of structure at the electronic level with abundant Se-vacancies and effective electronic coupling via an Ni-N-x coordination at the interface between the Ni0.85Se@NC core and NC shell. The Ni0.85Se@NC obtained exhibited low overpotentials for both oxygen evolution reaction (OER; 300 mV) and hydrogen evolution reaction (HER; 157 mV) at 10 mA.cm(-2) under an alkaline condition, outperforming their corresponding bulk MOF-derived counterparts. By exploiting Ni0.85Se@NC as anode and cathode catalysts, a low cell voltage of 1.61 V was achieved by performing alkaline water electrolysis. Remarkably, it also reached a high activity in natural seawater (pH = 7.98) and simulated seawater (pH = 7.86) electrolytes, even surpassing integrated Pt/C-RuO2/CC electrodes. Density functional theory (DFT) studies illustrated that abundant Se-vacancies effectively regulated the electronic structure of Ni0.85Se@NC by accelerating electron transfer from Ni to N atoms at the interface, and thus, enabling the Ni0.85Se@NC to attain a near-optimal electronic configuration that stimulated ideal adsorption-free energy toward key reaction intermediates. [GRAPHICS] .