Co3-xFexO4 inverse opals with tunable catalytic activity for high-performance overall water splitting

The development of earth-abundant and high-performance bifunctional catalysts for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in alkaline electrolytes is required to efficiently produce hydrogen by electrochemical water splitting, but remains a challenge. We have fabricated mesoporous cobalt iron oxide inverse opals (m-CFO IO) with different mole ratios of cobalt and iron by a wet chemical method using polystyrene beads as a hard template, followed by calcination in air. The performance of the m-CFO IO as OER and HER electrocatalysts was investigated. The as-prepared catalyst with equal concentrations of Fe and Co exhibits remarkable OER and HER performances with low overpotentials of 261 and 157 mV to attain 10 mA cm(-2) and small Tafel slopes of 63 and 56 mV dec(-1), respectively. An alkaline water electrolyzer with a two-electrode configuration achieves 10 mA cm(-2) at 1.55 V with excellent long-term stability, outperforming the combination of noble metal IrO2 and Pt/C benchmark catalysts. The superior catalytic performance is ascribed to the synergistic effects of particle size, crystallinity, oxygen efficiency, a large number of active sites, and the large specific surface area of the porous inverse opal structure.

Automated summary

The development of earth-abundant and high-performance bifunctional catalysts for electrochemical water splitting remains a challenge. In this study, mesoporous cobalt iron oxide inverse opals were fabricated with different mole ratios of cobalt and iron. The as-prepared catalyst with equal concentrations of Fe and Co exhibited remarkable OER and HER performances with low overpotentials and small Tafel slopes. It outperformed noble metal catalysts and showed excellent long-term stability, attributed to the synergistic effects of particle size, crystallinity, oxygen efficiency, active sites, and specific surface area.