Issue 20, 2021

Highly selective CO2 conversion to methane or syngas tuned by CNTs@non-noble–metal cathodes in Zn–CO2 flow batteries

Abstract

Metal–CO2 batteries represent a potential new technology for environmental protection, as they can effectively reduce CO2 emissions while ensuring energy production. However, the design of active, selective, and cost-efficient electrocatalysts remains a challenge. Herein, we report two tubular cathodes (CNTs@Cu and CNTs@Ni, CNTs = carbon nanotubes) that are used to assemble two primary Zn–CO2 flow batteries with zinc wire and 1-ethyl-3-methylimidazolium tetrafluoroborate as the anode and electrolyte, respectively. Interestingly, CO2 conversion with quite high selectivity could be realized over the different cathodes in these two Zn–CO2 flow batteries. These two batteries exhibit the advantages of high operating voltages, excellent stability, and continuous and selective product outputs. The flow battery based on the tubular CNTs@Cu cathode can convert CO2 into CH4 with a faradaic efficiency of up to 93.3%. Concurrently, electricity is generated at an energy density of 376 Wh kg−1. This battery remains stable for more than 18 days. Surprisingly, the flow battery with a tubular CNTs@Ni cathode can reduce CO2 to syngas (CO and H2, faradaic efficiencies for CO and H2 of up to 50% and 48%, respectively) while generating electricity at an energy density of 208.7 Wh kg−1, and it is stable for up to 9 days. These excellent performances are attributed to a synergistic effect involving CNTs and the metal substrate, and the differences between these two batteries are mainly ascribed to metal substrate effects. Excitingly, low concentrations of CO2 released by humans and simulated vehicle emissions could also be converted. This work demonstrates that Zn–CO2 flow batteries are green, selective, efficient, and promising devices for producing value-added chemicals, and they are worthy of further theoretical studies and practical application.

Graphical abstract: Highly selective CO2 conversion to methane or syngas tuned by CNTs@non-noble–metal cathodes in Zn–CO2 flow batteries

Supplementary files

Article information

Article type
Paper
Submitted
14 Jul 2021
Accepted
17 Sep 2021
First published
17 Sep 2021

Green Chem., 2021,23, 8138-8146

Highly selective CO2 conversion to methane or syngas tuned by CNTs@non-noble–metal cathodes in Zn–CO2 flow batteries

Y. Chen, Y. Mei, M. Li, C. Dang, L. Huang, W. Wu, Y. Wu, X. Yu, K. Wang, L. Gu, L. Liu and X. Cao, Green Chem., 2021, 23, 8138 DOI: 10.1039/D1GC02496E

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