Co-utilization of wastewater sludge and heavy metals for single-atom electrocatalytic reduction of gaseous CO2

Highlights•The utilization of sludge and heavy metal wastewater to convert CO2•EPS atomically disperse Ni onto an integrated gas diffusion electrode•N-enriched wastes are competitive to synthesize efficient Ni single atom catalysts•Protein of EPS plays the biggest role in synthesizing Nx-Ni coordinationSummarySynergetic management of waste activated sludge, heavy metals (HMs) and CO2 for their valorization and cyclic utilization is rarely reported. Herein, we employed sludge-derived extracellular polymeric substances (EPS) and HMs in wastewater to fabricate a gas diffusion electrode (GDE) for electrochemical CO2 reduction. This approach atomically dispersed Ni at each nanofiber of the GDE. Abundant N element in the EPS proved to play a key role in the formation of Nx-Ni (mixture of N3-Ni and N4-Ni) sites for highly efficient CO2 to CO conversion. The atomical Ni3+ shows high catalytic activity. Direct gaseous CO2 reduction in a membrane electrode assembly generated a current density up to 50 mA·cm−2 with CO:H2 ratio of ∼100 and ∼75% FECO under 2.69 cell voltage. This strategy takes advantage of all waste streams generated on site and consolidates traditionally separated treatment processes to save costs, produces value-added products and generates carbon benefits during wastewater treatment.