Double-metal-Ion-exchanged mesoporous zeolite as an efficient electrocatalyst for alkaline water oxidation: synergy between Ni−Cu and their contents in catalytic activity enhancement

Abstract

The kinetics of total water splitting is mostly hampered by the sluggish oxygen evolution reaction (OER) at the anode of the electrolyzer. Herein, we focus on the design of a cost-effective porous OER catalyst for efficient water to fuel conversion. A simple metal-ion-exchange protocol is adapted to implant electroactive metal centers in the mesoporous architecture of Zeolite Socony Mobil-5 (ZSM-5). OER-active Ni is incorporated as catalytic sites in the mesoporous ZSM-5. Further, simultaneous incorporation of both Ni2+ and Cu2+ into the mesoporous ZSM-5 (Meso-Z) matrix significantly boost the OER catalytic activity. The optimization of Ni and Cu contents (1.04 wt % Ni and 0.44 wt % Cu) in the catalyst is found to be essential to achieve high catalytic activity. The Cu content influences the onset potential, and the Ni content determines the catalytic current during OER. Among developed catalysts, Ni2Cu1-Meso-Z offers the best performance even better than the state-of-art OER catalyst IrO2. Ni 2Cu1-Meso-Z delivers a current density of 10 mA/cm2 at an overpotential of 407 mV and exhibits a low Tafel slope of 55 mV/dec, a high electrochemical active surface area of 6.26, and a roughness factor of 89.42. Moreover, Ni2Cu1-Meso-Z retains 92% of its initial current density after 1000 potential cycles of a test run. The best performing Ni2Cu1Meso-Z offers a faradic efficiency of 92%, whereas the state-of-the-art IrO2 efficiency was decreased by 22% under the similar experimental condition. Further, Ni2Cu1-Meso-Z-modified anode exhibits better performance in its single cell than IrO2, in which Pt is used as cathode. The excellent OER catalytic activity of double-metal-ion-exchanged Meso-Z is attributed to the large surface area of mesoporous ZSM-5, hydrophilicity, fast diffusion of water molecules through the favorable interaction with Si− OH groups, and optimum binding and dissociation of different oxygeneous OER intermediates on the catalyst surface. Excellent current density and sustainable performance suggest that the double-metal-ion-exchanged mesoporous zeolite can serve as a potential candidate to improve the overall water splitting in the electrolyzer.