Cu–Ni Alloy Nanoparticles Anchored on Nitrogen-Doped Carbon Nanotubes for Efficient CO₂ Electroreduction to CO

Abstract

Efficient conversion of CO2 to value-added fuels or chemicals using electricity from renewable sources is an appealing approach to realize carbon neutrality. Under this background, it is crucial to design efficient and low-cost catalysts for CO2 electroreduction. Herein, we fabricated an electrocatalyst with the structure of Cu–Ni alloy nanoparticles grown on nitrogen-doped carbon nanotubes (Cu x Ni/NCNT, x = 2.4, 1, and 0.36) for electrochemical CO2 reduction reaction (CO2RR) via a hydrothermal method followed by pyrolysis. The optimized CuNi/NCNT demonstrates a favorable CO2RR performance with a CO Faradaic efficiency (FECO) of 94.8% and a current density of 26.6 mA cm–2 at −0.9 V versus the reversible hydrogen electrode (vs RHE) in the H-cell, far superior to those of single metal counterparts. Density functional theory (DFT) calculations unravel that the Cu–Ni alloys possess much lower free energy changes for the formation of the key COOH* intermediate than those of the Cu metal, thereby facilitating CO2 reduction into CO. Additionally, the CO2RR performance of CuNi/NCNT was further evaluated in the gas diffusion electrode (GDE) involved in the flow cell to examine the practical application of the prepared catalyst, which can deliver a current density of 124.6 mA cm–2 with a FECO of 92.8% at −1.1 V vs RHE. This work enriches electrocatalysts for highly efficient CO2 electroreduction to CO.

CuNiZn vs CuZn Electrodes: Electrochemical CO2 Reduction, Role of Metal Elements, and Insights for C–C Coupling Chemistry

“…32,33 The production of CO involved Cu−Ni alloy nanoparticles. 34 In the case of Cu 1−x Ni x , an increase in Ni content shifted the major products from C 2 compounds (C 2 H 4 and C 2 H 5 OH) to C 1 products (CH 4 and HCOO − ). 35 The support effect played a crucial role in the C 2 H 5 OH production of NiCu alloy on carbon nanofibers, involving the dimerization of CO. 36 For CuNiZn alloy, 40,41 Park et al demonstrated formate as the dominant product in a 0.1 M KHCO 3 electrolyte, with the additional meaningful production of long-chain C 2−7 hydrocarbons (C n H 2n+2 and C n H 2n ), explained by FT synthesis.…”

“…In the Cu 2p XPS profiles (Figure 9a), Cu 2p 3/2 and Cu 2p 1/2 peaks at 932.2 and 952.1 eV, respectively, were assigned to Cu/ Cu 2 O. 15,34,35,40 The Cu 2p 3/2 peak at 934.4 eV, attributed to CuO, 15,34,35,40 was distinctly observed and removed after sputtering. The CuO peak became much weaker after the EC test at −2.0 V (Figure 9b).…”

“…In the Cu 2p XPS profiles (Figure 8a), Cu 2p 3/2 and Cu 2p 1/2 peaks at 932.2 and 952.1 eV, respectively, were assigned to Cu/ Cu 2 O. 15,34,35,40 A weaker peak at 934.4 eV indicated CuO. Post sputtering, the major peaks substantially increased, reflecting the removal of overlayer species like carbon impurities and adsorbed water.…”

“…For Ni 2p XPS profiles (Figure 8a2), Ni 2p 3/2 and Ni 2p 1/2 peaks at 852.0 and 869.3 eV, respectively, were attributed to metallic Ni, while the Ni 2p 3/2 peak at 855.6 eV was attributed to Ni(II) oxides. 34,35,40 The Ni oxide peak was stronger before sputtering, but the metallic peak became more dramatically enhanced, indicating a Ni oxide surface with a metallic Ni core. After EC tests (Figure 8b2), the Ni 2p peak positions were similar but appeared weaker.…”

“…Pure, bi- and trimetals have been extensively employed as electrodes in electrochemical CO 2 reduction (EC CO 2 R). − The combination of two or three different metals has revealed unique reduction products and new channels for reduction, as observed in cases like CuZn, − CuNi, − and CuNiZn. , Considering only three metal elements, Cu, Ni, and Zn, in the case of CuZn, CO was predominantly generated over bare CuZn, whereas membrane-modified CuZn exhibited a higher propensity for C 2 H 4 production through CO–CO coupling . Baek et al emphasized the significance of the Zn/Cu ratio in determining the selectivity between C 2 H 4 and C 2 H 5 OH, with the Cu 2 Zn 1 ratio maximizing the C 2 H 5 OH/C 2 H 4 ratio .…”