Co-utilization of Wastewater Sludge and Heavy Metals for Single-Atom Electrocatalytic Reduction of Gaseous CO2

Synergetic management of waste activated sludge, heavy metals and CO2 for their valorization and cyclic utilization is rarely reported. Herein, we employed sludge-derived extracellular polymeric substances (EPS) and heavy metals 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.