Electrodeposition of Cu-based catalysts for the electrochemical conversion of CO₂ to valuable chemicals and renewable fuels

Abstract

Electrochemical carbon dioxide reduction (CO2R) is a promising technology for sustainably storing renewable energy and producing carbon-based chemicals. To commercialise CO₂R, catalysts must achieve high selectivity and efficiency at low energy costs. However, achieving reproducible gas diffusion electrodes (GDEs) remains a challenge, as small variations in preparation can lead to variations in features such as surface uniformity, morphology and catalyst loading. This research follows a systematic approach to address these challenges by optimising the fabrication of GDEs for CO₂R. Electrodeposition, a widely used and time-efficient technique for synthesising Cu catalysts, plays a central role in this process. Its precise control over surface morphology, crystal orientation, and alloying with other elements enables the production of catalysts with tailored activity and selectivity. By ensuring reproducibility in GDE fabrication, electrodeposition provides a fundamental solution for advancing the commercial viability of CO₂R. The manufacturing of CO₂ catalysts by electrodeposition begins by carefully ’activating’ a commercial carbonaceous gas diffusion layer (GDL) using HNO₃, which makes the surface sufficiently hydrophilic, so that droplets remain on the surface rather than penetrating the GDL bulk for uniform catalyst electrodeposition, while maintaining the bulk hydrophobicity to prevent flooding during electrolysis.

Key electrodeposition parameters, including pH, temperature, current density, and catalyst load, were optimised under galvanostatic conditions, achieving reproducible GDEs with uniform Cu catalyst distribution. Cu GDEs with 5 cm² showed a CO₂R Faradaic efficiency of 70% at 200 mA cm⁻², while material use was reduced by 50% (1 compared with 2 C cm⁻²) and electrodeposition time by 75% (30 vs. 15 mA cm−2 at 1 C cm⁻²).

To enhance product selectivity towards C₂₊ products and suppress the competing hydrogen evolution reaction, Cu was alloyed with Ag to produce bimetallic CuAg catalysts. Citrate was used as a stabilising additive to enable uniform deposition and improve electrolyte stability. CuAg catalysts deposited at 15 mA cm−2 with a catalyst loading of 2 C cm⁻² exhibited the best overall performance, achieving C₂₊ Faradaic efficiency of 73% at 200 mA cm⁻², with high selectivity for ethylene and alcohols while reducing HER to less than 20%. At 200 mA cm⁻², Cu exhibited slightly higher energy efficiency, whereas CuAg favoured C₂₊ products, particularly alcohols, indicating more effective utilisation of CO intermediates.

The combination of morphological control, catalyst integration, and electrochemical evaluation presented in this work provides a scalable and reproducible strategy for GDE fabrication. This approach contributes to the advancement of efficient, cost-effective, and industrially relevant CO₂ electroreduction technologies.