NiFe-based tungstate@layered double hydroxide heterostructure supported on graphene as efficient oxygen evolution reaction catalyst

Abstract

Oxygen evolution reaction (OER) plays a key role in water splitting and rechargeable metal–air batteries, thus eagerly demanding efficient, robust, and low-cost electrocatalysts. Two-dimension layered double hydroxides (LDHs) have been widely recognized as one of the most promising OER catalysts due to the high activity and large specific surface area. However, the insufficient electrical conductivity and resistance against corrosion seriously restrict their capabilities of charge transport and long-term stability. Herein, a NiFe-based heterostructure catalyst is proposed by the coupling of NiFe-based LDH (termed NiFe-LDH) nanosheets and amorphous NiFe-tungstate (termed NiFeWO4) nanoparticles, both of which possess the same stoichiometric Ni/Fe ratio (3:1), on graphene substrate (termed NiFeWO4@NiFe-LDH/G). Attributed to the synergy of individual components, NiFeWO4@NiFe-LDH/G exhibits superb electrocatalytic activity for OER in an alkaline electrolyte, with extremely low overpotential of 222 mV at a current density of 10 mA cm-2 and Tafel slope of 32.1 mV dec-1, far surpassing the benchmark IrO2 catalyst. Furthermore, NiFeWO4@NiFe-LDH/G exhibits superior stability and durability to IrO2. Comprehensive characterizations and electrochemical measurements together with DFT calculations reveal that the hetero-assembly of NiFe-LDH and NiFeWO4 generates more efficient NiFe active sites than that of the individual components via a strong chemical binding interaction, which can modulate the electronic structures and optimize the energetics of active sites for OER intermediates. As a result, a low cell voltage of 1.48 V is achieved for the water splitting in two-electrode Pt/C‖NiFeWO4@NiFe-LDH/G electrolysis cell at 10 mA cm-2, overwhelmingly prevailing over the 1.69 V for the Pt/C‖IrO2 benchmark cell. This work provides an ingenious heterostructure design for efficient and stable OER electrocatalysts.