2.6% cm–2 Single-Pass CO2-to-CO Conversion Using Ni Single Atoms Supported on Ultra-Thin Carbon Nanosheets in a Flow Electrolyzer

The CO2 reduction reaction (CO2RR) using a renewable energy source is a promising strategy for its utilization. Such a technology, however, requires the development of catalysts with optimized activity and selectivity that can be integrated into the device architectures. Flow electrolyzers have recently been proposed for facilitating the electrochemical CO2RR thanks to their unique ability to perform electroreduction at high reaction rates via the creation of the three-phase interface. While some examples of flow electrolyzers for the conversion of CO2 have recently been reported, the influence of the CO2 and electrolyte streams on the overall catalytic mechanism remained ambiguous. Here, we synthesized single-atom nickel on two-dimensional nitrogen-doped carbon nanosheets (SA Ni-NC) for the CO2-to-CO conversion. Taking advantage of this model catalyst, we explored the correlation between the applied potential and the feeds in both electrolyte and CO2, on the one hand, and the performance metrics, on the other hand. By regulating the feed stream's conditions, the SA Ni-NC achieves energy efficiencies as high as 85% at jCO = 7.2 mA cm–2 and 56% at jCO = 170 mA cm–2, whereas the single-pass CO2-to-CO conversion efficiency (SPCC) reaches 2.6% cm–2. We finally demonstrated the scalability of the flow electrolyzers by stacking three 1 cm2 reactors and reached a record-high CO yield rate of 31.5 L min–1 m–2 with near-unity CO selectivity and an SPCC of 8.9% from three.