A bismuth-atom electrocatalyst for a stable and economical aqueous Zn–CO2 battery

Abstract

Aqueous Zn–CO₂ batteries are emerging as a promising technology for efficiently utilizing excessive atmospheric CO₂ while storing renewable electricity. The development of Zn–CO₂ batteries requires cathodes containing electrocatalysts with high catalytic activity to boost the efficiency of the electrochemical reduction of CO₂ (CO₂RR). However, current electrocatalyst-based cathodes face several challenges, such as low hydrocarbon products and high cost. This work develops a single-atom bismuth anchored N-doped carbon (Bi-SAs/NC) electrocatalyst as an effective cathode for a Zn–CO₂ battery. The electrochemical properties of Bi-SAs/NC were assessed using an H-type cell in 0.5 M KHCO₃ and in situ Gas Chromatography (GC) with a continuous gas supply of CO₂. No notable gaseous products were observed apart from H₂. Furthermore, ex situ nuclear magnetic resonance analysis showed the presence of small hydrocarbons, such as formic acid (HCOOH), ethane-diol (CH₃CH(OH)₂), acetic acid (CH₃COOH) and acetaldehyde (CH₃CHO) at very low faradaic efficiency. Despite low efficiencies in producing higher hydrocarbons, the presence of carbon-containing intermediates (e.g., *CO and *HCO) is perceptible. Notably, these carbon species play a vital role in enabling the formation of C₂₊ products. Moreover, we demonstrate the potential of Bi-SAs/NC in Zn–CO₂ devices, showing exceptional performance with a high current density of 14 mA cm⁻² and an elevated power density of 3.2 mW cm⁻². Long-term charge and discharge cycling of the Zn–CO₂ battery continues for 67 h at 0.5 mA cm⁻², highlighting its cycling stability and durability. Lastly, the results presented exhibit a viable strategy for developing Zn–CO₂ batteries with enhanced values of current and power densities attributed to the presence of a high number of defects and higher electrochemical active surface area of Bi-SAs/NC. We explore the potential of further reducing the cost and environmental impacts of the proposed Zn–CO₂ battery by comparing a fresh zinc anode with a recycled and cleaned zinc anode for use in the cell.