Alloying Cu, Fe, and Co in Ni/YSZ Electrodes for High-Temperature CO2 Electrolysis: Impact on TPB Density, Activity, and Carbon Deposition Resistance

Abstract

Electrochemical CO₂ reduction using solid oxide electrolysis cells (SOECs) directly converts CO2 into value‑added chemicals, mitigating greenhouse‑gas emissions. Nickel (Ni) is the conventionally used fuel‑electrode electrocatalyst, yet its intrinsic catalytic behavior is underexplored. This study systematically evaluates Ni alloyed with 5 at% Fe, Co, or Cu for changes in microstructure, electrochemical activity, and carbon coking resistance. Model electrodes fabricated by pulsed laser deposition are analyzed by scanning and transmission electron microscopy, X‑ray diffraction, and X‑ray absorption spectroscopy, which confirm homogeneous alloy formation and show that additive metals modulate active site density by modulating sintering behavior, thereby tuning the triple-phase-boundary density in the order Ni > Ni–Cu > Ni–Co > Ni–Fe. Electrochemical impedance spectroscopy reveals that the apparent activation energy (Ea) related to surface reaction decreases for all samples, accelerating CO2 electrolysis, while sensitivity to the CO/CO2 ratio rises when the alloying element is less prone to CO2 dissociation. Diffuse reflectance Fourier‑transform infrared spectroscopy and density functional theory calculations indicate that Co and Fe facilitate CO2 dissociation, whereas Cu facilitates fast desorption of product species and enhances turnover activity. Cu alloying markedly suppresses carbon coking, whereas Co exacerbates it. Enhanced performance and durability are validated by impedance and Galvano-static measurements. These findings demonstrate that Ni–Cu alloy electrodes offer a practical route to boost SOEC efficiency and mitigate coking with minimal structural change.