Regulating Charge Diffusion of Two-Dimensional Cobalt-Iron Hydroxide/Graphene Composites for High-Rate Water Oxidation
Although the significance of charge diffusion has been recognized in many high-performance energy devices, it received much less attention in designing electrocatalysts for oxygen evolution reaction (OER), which particularly crucial for highly-active but less conductive OER electrocatalysts such as two-dimensional metal hydroxides (MHs) with anisotropic conductivity. Herein, a series of CoFe hydroxide nanosheets on graphene (CFH@G) composites are elaborately designed to demonstrate the importance of charge diffusion regulation in improving the OER activity of MHs. It is discovered that the few-layer thick CFH nanosheets lying on the graphene substrate endow the effective in-plane charge diffusion pathway while keeping the substrate surface entirely covered by laid nanosheets is necessary for providing sufficient active sites. The over thick or stacked nanosheets are not favourable for charge diffusion, especially at large current outputs. By regulating the charge diffusion property, the best-performed CFH@G-based material can deliver a steady OER current density of 2000 mA cm-2 at a cost of only 1.507 V under near-industrial condition (6 M KOH & 60 oC). A practical water electrolyzer also demonstrates an impressive current output of 400 mA cm-2 at 1.694 V as well as a steady solar-to-hydrogen efficiency of 17.41%. These findings provide new insights into the role of charge diffusion in water oxidation and may open up an avenue for developing low-cost, stable and efficient electrocatalysts for practical water electrolysis and diverse energy devices.
- This article is part of the themed collection: Journal of Materials Chemistry A HOT Papers