Highly active oxygen evolution integrated with efficient CO2 to CO electroreduction

Yongtao Meng; Xiao Zhang; Wei-Hsuan Hung; Junkai He; Yi-Sheng Tsai; Yun Kuang; Michael J Kenney; Jing-Jong Shyue; Yijin Liu; Kevin H Stone; Xueli Zheng; Steven L Suib; Meng-Chang Lin; Yongye Liang; Hongjie Dai

doi:10.1073/pnas.1915319116

Highly active oxygen evolution integrated with efficient CO₂ to CO electroreduction

Proc Natl Acad Sci U S A. 2019 Nov 26;116(48):23915-23922. doi: 10.1073/pnas.1915319116. Epub 2019 Nov 13.

Authors

Yongtao Meng^{1

2}, Xiao Zhang^{2

3}, Wei-Hsuan Hung^{2

4}, Junkai He⁵, Yi-Sheng Tsai⁴, Yun Kuang², Michael J Kenney², Jing-Jong Shyue⁶, Yijin Liu⁷, Kevin H Stone⁷, Xueli Zheng⁸, Steven L Suib⁵, Meng-Chang Lin¹, Yongye Liang³, Hongjie Dai⁹

Affiliations

¹ College of Electrical Engineering and Automation, Shandong University of Science and Technology, 266590 Qingdao, China.
² Department of Chemistry, Stanford University, Stanford, CA 94305.
³ Department of Materials Science and Engineering, South University of Science and Technology of China, 518055 Shenzhen, China.
⁴ Institute of Materials Science and Engineering, National Central University, 32001 Taoyuan, Taiwan.
⁵ Institute of Materials Science, University of Connecticut, Storrs, CT 06269.
⁶ Research Center of Applied Science, Academia Sinica, 115 Taipei, Taiwan.
⁷ Stanford Synchrotron Radiation Light Source, SLAC National Accelerator Laboratory, Menlo Park, CA 94025.
⁸ Department of Material Science and Engineering, Stanford University, Stanford, CA 94305.
⁹ Department of Chemistry, Stanford University, Stanford, CA 94305; hdai1@stanford.edu.

Abstract

Electrochemical reduction of CO₂ to useful chemicals has been actively pursued for closing the carbon cycle and preventing further deterioration of the environment/climate. Since CO₂ reduction reaction (CO₂RR) at a cathode is always paired with the oxygen evolution reaction (OER) at an anode, the overall efficiency of electrical energy to chemical fuel conversion must consider the large energy barrier and sluggish kinetics of OER, especially in widely used electrolytes, such as the pH-neutral CO₂-saturated 0.5 M KHCO₃ OER in such electrolytes mostly relies on noble metal (Ir- and Ru-based) electrocatalysts in the anode. Here, we discover that by anodizing a metallic Ni-Fe composite foam under a harsh condition (in a low-concentration 0.1 M KHCO₃ solution at 85 °C under a high-current ∼250 mA/cm²), OER on the NiFe foam is accompanied by anodic etching, and the surface layer evolves into a nickel-iron hydroxide carbonate (NiFe-HC) material composed of porous, poorly crystalline flakes of flower-like NiFe layer-double hydroxide (LDH) intercalated with carbonate anions. The resulting NiFe-HC electrode in CO₂-saturated 0.5 M KHCO₃ exhibited OER activity superior to IrO₂, with an overpotential of 450 and 590 mV to reach 10 and 250 mA/cm², respectively, and high stability for >120 h without decay. We paired NiFe-HC with a CO₂RR catalyst of cobalt phthalocyanine/carbon nanotube (CoPc/CNT) in a CO₂ electrolyzer, achieving selective cathodic conversion of CO₂ to CO with >97% Faradaic efficiency and simultaneous anodic water oxidation to O₂ The device showed a low cell voltage of 2.13 V and high electricity-to-chemical fuel efficiency of 59% at a current density of 10 mA/cm².

Keywords: CO2 electrolyzer; CO2 reduction; electrocatalysis; oxygen evolution; pH-neutral electrolyte.