Metal-free carbon-based nanomaterials for electrochemical nitrogen and carbon dioxide reductions

To relieve greenhouse effect and energy crisis, the clean powers are growing to hold heavy shares, and electrolysis is a necessary supporting technique for large-scale conversion or long-term storage of the electricity. The electrocatalytic reductions, converting inert molecules (nitrogen and carbon dioxide) into high-value chemicals or fuels under mild conditions, have attracted tremendous attentions. In this scene, a high-surface-area conductive catalytic porous gas-diffusion-electrode is highly desired. Carbon nanomaterials as either active components or supports are being increasingly exploited for their large surface, conductance, abundance and low cost. The strategy of heteroatom doping in carbons is recently accentuated towards high catalytic performances, resulting from the regulation of electronic structures. In this review, the doping effect of the single element (N, S, B, O and P) in carbon-based nonmetallic electrocatalysts is surveyed for nitrogen and carbon dioxide reductions. The synergistic doping of double elements is also discussed. The challenges and prospects are additionally deliberated. It is envisaged that a comprehensive overview will spur the majorization of metal-free carbon-based electrocatalysts. This review thus aims to provide a guidance for the proof-of-concept design of efficient electrocatalysts to surmount present scientific bottlenecks.