Ni-based electrocatalysts for unconventional CO2 reduction reaction to formic acid

Electrochemical reduction stands as an alternative to revalorize CO2. Among the different alternatives, Ni single atoms supported on carbonaceous materials are an appealing catalytic solution due to the low cost and versatility of the support and the optimal usage of Ni and its predicted selectivity and efficiency (ca. 100% towards CO). Herein, we have used noble carbonaceous support derived from cytosine to load Ni subnanometric sites. The large heteroatom content of the support allows the stabilization of up to 11 wt% of Ni without the formation of nanoparticles through a simple impregnation plus calcination approach, where nickel promotes the stabilization of C3NOx frameworks and the oxidative support promotes a high oxidation state of nickel. EXAFS analysis points at nickel single atoms or subnanometric clusters coordinated by oxygen in the material surface. Unlike the well-known N-coordinated Ni single sites selectivity towards CO2 reduction, O-coordinated-Ni single sites (ca. 7 wt% of Ni) reduced CO2 to CO, but subnanometric clusters (11 wt% of Ni) foster the unprecedented formation of HCOOH with 27% Faradaic efficiency at − 1.4 V. Larger Ni amounts ended up on the formation of NiO nanoparticles and almost 100% selectivity towards hydrogen evolution. [Display omitted] •Ni was loaded on nitrogen-doped carbonaceous materials from decomposition of organic complexes in air.•Due to the high surface area and nitrogen content, materials present high loading of nickel as single atoms (up to 10%).•EXAFS analysis suggests that Ni sub-nanomeric clusters starts growing at 10% in loading.•EXAFS points at Ni-O coordination sites and DFT studies to nitrogen helping stabilizing nickel single sites.•The Ni-based materials performed as catalysts for CO2RR giving different selectivity compared to literature.