A high-performance oxygen evolution catalyst in neutral-pH for sunlight-driven CO2 reduction

Li Qin Zhou,Chen Ling,Chongmin Wang,Liangzi Deng,Yan Yao,Joseph Liao,Gunugunuri K Reddy,Ruigang Zhang,Hui Zhou,Xiang Wang,Hongfei Jia,Torin C Peck,M Stanley Whittingham,Ching-Wu Chu

doi:10.1038/s41467-019-12009-8

Abstract

The efficiency of sunlight-driven reduction of carbon dioxide (CO2), a process mimicking the photosynthesis in nature that integrates the light harvester and electrolysis cell to convert CO2 into valuable chemicals, is greatly limited by the sluggish kinetics of oxygen evolution in pH-neutral conditions. Current non-noble metal oxide catalysts developed to drive oxygen evolution in alkaline solution have poor performance in neutral solutions. Here we report a highly active and stable oxygen evolution catalyst in neutral pH, Brownmillerite Sr2GaCoO5, with the specific activity about one order of magnitude higher than that of widely used iridium oxide catalyst. Using Sr2GaCoO5 to catalyze oxygen evolution, the integrated CO2 reduction achieves the average solar-to-CO efficiency of 13.9% with no appreciable performance degradation in 19 h of operation. Our results not only set a record for the efficiency in sunlight-driven CO2 reduction, but open new opportunities towards the realization of practical CO2 reduction systems.

Highlights

The efficiency of sunlight-driven reduction of carbon dioxide (CO2), a process mimicking the photosynthesis in nature that integrates the light harvester and electrolysis cell to convert CO2 into valuable chemicals, is greatly limited by the sluggish kinetics of oxygen evolution in pH-neutral conditions
Significant improvements have been achieved in studying CO2 reduction (CO2R) and oxygen evolution reaction (OER) in half-cells[2,3], and various valuable carbon-based products have been synthesized in the lab demonstration of integrated devices, including carbon monoxide (CO), formate, hydrocarbons, and oxygenates[4,5,6,7,8,9,10]
Oxygen atom is missed from octahedral GaO6 in a normal perovskite, resulting in CoO6 octahedra and GaO4 tetrahedra stacked alternatingly, which are clearly visible in the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image (Fig. 1b)

Summary

Introduction

The efficiency of sunlight-driven reduction of carbon dioxide (CO2), a process mimicking the photosynthesis in nature that integrates the light harvester and electrolysis cell to convert CO2 into valuable chemicals, is greatly limited by the sluggish kinetics of oxygen evolution in pH-neutral conditions. A promising approach to meet this challenge is to store solar energy in chemical bonds through sunlight-driven reduction of CO21 This process pairs two half-reactions of CO2 reduction (CO2R) and oxygen evolution reaction (OER) and powers the electrochemical cell using the photocurrents generated from one or more light absorbers. Previous studies widely used noble metal oxide such as IrO2 to catalyze OER in neutral pH;[4,5,6,14] but the moderate activity of IrO2 limited the STF efficiency below 7%11 This challenge was circumvented by isolating CO2R and OER in different pH-valued solutions using bipolar membrane (BPM)[8,9,10]. Whereas the introduction of BPM allowed the operation of CO2R and OER in optimal environments to achieve higher STF efficiency over 10% and potentially benefited the separation of product gases, it caused additional membrane-derived voltage losses and raised extra complexity of optimization[14,15,16], but the ion crossover due to imperfection of the BPM is still a concern for a long-term operation[8]

Methods

Results

Conclusion