A high CO2 to CO electroreduction rate exceeding 300 mA cm−2 was achieved with single atom nickel and nitrogen doped three-dimensional porous carbon electrocatalysts.

The electrochemical reduction of carbon dioxide (CO ) to value-added products is a promising approach to reducing excess CO in the atmosphere. However, the development of electrocatalysts for highly selective and efficient electrochemical CO reduction has been challenging because protons are usually easier to reduce than CO in an aqueous electrolyte. Recently, single-atom catalysts (SACs) have been suggested as candidate CO reduction catalysts due to their unique catalytic properties. To prepare single-atom metal active sites, the stabilization of metal atoms over conductive supports such as graphene sheets to prevent metal aggregation is crucial. To address this issue, a facile method was developed to prepare single-atom nickel active sites on reduced graphene oxide (RGO) sheets for the selective production of carbon monoxide (CO) from CO . The tris(2-benzimidazolylmethyl)amine (NTB) ligand was introduced as a linker that can homogeneously disperse nickel atoms on the graphene oxide (GO) sheets. Because the NTB ligands form strong interactions with the GO sheets by π-π interactions and with nickel ions by ligation, they can effectively stabilize nickel ions on GO sheets by forming Ni(NTB)-GO complexes. High-temperature annealing of Ni(NTB)-GO under inert atmosphere produces nickel- and nitrogen-doped reduced graphene oxide sheets (Ni-N-RGO) with single-atom Ni-N active sites. Ni-N-RGO shows high CO reduction selectivity in the reduction of CO to CO with 97 % faradaic efficiency at -0.8 V vs. RHE (reversible hydrogen electrode).

Structurally ordered intermetallic compounds are proven to be very promising for electrocatalysis owing to the homogeneous distribution of active sites, thermodynamic stability, and resistance toward surface rearrangement. Herein, we demonstrate a facile route for the synthesis of Sn-and Pd-based ordered intermetallics hybridized with reduced graphene oxide (rGO) and their bifunctional electrocatalytic performance toward oxygen reduction (ORR) and ethylene glycol oxidation reactions (EGOR). The coreduction of SnCl 2 and K 2 PdCl 4 in 1,5pentanediol in the presence of graphene oxide and the subsequent thermal annealing in an inert atmosphere affords rGO hybridized intermetallics of three phases: primitive orthorhombic PdSn, base-centered orthorhombic PdSn 2 , and hexagonal Pd 3 Sn 2 . The electrocatalytic performance of the hybrid intermetallics toward EGOR and ORR is evaluated in alkaline and acidic electrolytes. Among the three intermetallics, PdSn has excellent electrocatalytic performance toward EGOR and ORR. The PdSn/rGO hybrid catalyst outperforms the other two intermetallics toward EGOR in alkaline pH and ORR in acidic as well as alkaline pH in terms of onset potential and mass specific activity. The enhanced performance of PdSn/rGO catalyst is attributed to (i) a change in the Pd dband center, (ii) a Pd−Pd interatomic distance in a unit cell, and (iii) weak adsorption of in-situ-generated oxygen-containing intermediates species. The lattice strain due to the presence of dissimilarly sized Sn and Pd in a unit cell and the high oxophilicity of Sn downshifts the d-band center of Pd and facilitate the electron transfer kinetics. The catalyst support, rGO, prevents the unwanted aggregation of the active catalyst. The density functional theory calculations show that the oxygen-containing species weakly adsorb on the PdSn surface compared to the other intermetallics, supporting the high electrocatalytic activity of PdSn/rGO.