Carbon Fiber Paper Working Electrodes for CO2 Reduction Electrocatalysis

Rapid climate change is threatening the world as we know it. Climate change is caused by global warming, primarily due to the release of greenhouse gases, such as CO₂. Carbon dioxide emissions continue to rise at an alarming rate by burning fossil fuels, cement production, and deforestation. If no further action is taken to curb continued anthropogenic CO₂ emissions, devastating impacts on the planet are inevitable, such as heatwaves, droughts, wildfires, and decline in water and food supplies. Successor technologies must be developed now to combat climate change; one such sustainable technology is aqueous electrocatalysis to convert carbon dioxide to valuable fuels and chemicals.

Inexpensive, electrically conductive, high surface area electrode materials, such as carbon fiber paper, are needed for globally scalable electrolyzers. A large obstacle to the wide-spread use of carbon fiber paper is its high hydrophobicity; electrocatalysis in aqueous media requires hydrophilic surfaces to maximize the contact area between nanocatalysts and the electrolyte.

Here we present methods to increase the hydrophilicity of carbon fiber paper. We systematically investigated how different treatments affected surface chemistries. We were able to show that distinct surface species correlated with the durability of hydrophilicity. We characterized carbon fiber paper samples by high-resolution X-ray photoelectron spectroscopy and scanning electron microscopy imaging with energy-dispersive X-ray spectroscopic elemental mapping.

We used treated carbon fiber paper to immobilize ca. 20 nm gold nanoparticles on these electrodes, using commercial aqueous citrate-capped gold colloid, for CO₂ reduction electrocatalysis. Scanning electron microscopy images showed that gold nanoparticles were evenly distributed on carbon fibers. Hydrogen was the predominant product in CO₂-saturated aqueous 0.1 M pH 6.8 KHCO₃ electrolyte; the only other detected product was CO. We note that citrate capping of gold nanoparticles enhances hydrogen production, which explains the observed high faradaic efficiencies for hydrogen. During chronoamperometry testing, currents initially decayed, likely attributable to the reduction of native oxide. After this induction period currents were stable, indicating that immobilization of gold nanoparticles on treated carbon fiber paper was successful.