Nanostructural design of flexible mesoporous hydrogel electrodes via colloidal electrochemical deposition for highly efficient oxygen evolution reaction

Abstract

Water electrolysis is a core technology for converting renewable energy into hydrogen and is useful for energy storage and transportation. Porous electrodes can efficiently promote the oxygen evolution reaction (OER) because of their high surface area; however, the generated bubbles block the electrode surface and reduce the number of reaction sites. Here, we demonstrate flexible mesoporous hydrogel electrodes with more than 90% porosity prepared by the colloidal electrochemical deposition of hybrid cobalt hydroxide nanosheets (Co-ns) as promising new materials for porous OER electrodes in alkaline media, combining a large surface area with high mass transport. The pore size of the flexible mesoporous hydrogel electrodes was controlled in the range of 25–45 nm by controlling the lateral size of the Co-ns. The pore surfaces of the flexible mesoporous hydrogel electrodes with larger pore sizes were utilized more efficiently in the depth along the thickness direction, demonstrating higher mass transport. Colloidal electrochemical deposition is also useful for constructing hierarchical structures, such as bilayer electrodes combining differently sized mesopores, placing larger pores with high mass transport in the top layer and small pores with a high surface area in the bottom layer, thereby achieving a higher OER current density than monolayer electrodes. Flexible mesoporous hydrogel electrodes, with facile control over mesopores and hierarchical structures, show great potential as new forms of mesoporous electrodes for water electrolysis.