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

Synergetic management of waste activated sludge, heavy metals (HMs) and CO 2 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 CO 2 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 N x -Ni (mixture of N 3 -Ni and N 4 -Ni) sites for highly efficient CO 2 to CO conversion. The atomical Ni 3+ shows high catalytic activity. Direct gaseous CO 2 reduction in a membrane electrode assembly generated a current density up to 50 mA·cm −2 with CO:H 2 ratio of ∼100 and ∼75% FE CO 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.