Bifunctional Nickel-Nitrogen-Doped-Carbon-Supported Copper Electrocatalyst for CO2 Reduction

Bifunctionality is a key feature of many industrial catalysts, supported metal clusters and particles in particular, and the development of such catalysts for the CO2 reduction reaction (CO2RR) to hydrocarbons and alcohols is gaining traction in light of recent advancements in the field. Carbonsupported Cu nanoparticles are suitable candidates for integration in the state-ofthe-art reaction interfaces, and here, we propose, synthesize, and evaluate a bifunctional Ni-N-doped-C-supported Cu electrocatalyst, in which the support possesses active sites for selective CO2 conversion to CO and Cu nanoparticles catalyze either the direct CO2 or CO reduction to hydrocarbons. In this work, we introduce the scientific rationale behind the concept, its applicability, and the challenges with regard to the catalyst. From the practical aspect, the deposition of Cu nanoparticles onto carbon black and Ni-N-C supports via an ammonia-driven deposition precipitation method is reported and explored in more detail using X-ray diffraction, thermogravimetric analysis, and hydrogen temperature-programmed reduction. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy (EDXS) give further evidence of the presence of Cu-containing nanoparticles on the Ni-N-C supports while revealing an additional relationship between the nanoparticle's composition and the electrode's electrocatalytic performance. Compared to the benchmark carbon black-supported Cu catalysts, Ni-N-C-supported Cu delivers up to a 2-fold increase in the partial C2H4 current density at -1.05 V-RHE (C-1/C-2 = 0.67) and a concomitant 10-fold increase of the CO partial current density. The enhanced ethylene production metrics, obtained by virtue of the higher intrinsic activity of the Ni-N-C support, point out toward a synergistic action between the two catalytic functionalities.