Converting Energy with Glycerol and CO₂ in a Microfluidic Fuel Cell Equipped with CuBiO₄/CuO Photocathode: Bypassing Bubbles Challenge of Concurrent Water Splitting

The imperative to address CO₂ emissions has prompted the search for alternative approaches to capture this gas with minimal energy consumption. In this context, leveraging the CO₂ reduction reaction (CO₂RR) as an oxidant in fuel cells has emerged as a sophisticated strategy to convert this gas into usable energy. This study introduces a hybrid microfluidic photo fuel cell (μPFC) designed for the efficient conversion of CO₂ and glycerol into electrical energy. The prototype integrates 3D-printed components with glass sealing, enabling precise control over the reactant flow and the use of light-sensitive catalysts. The anodic glycerol electrooxidation was investigated on Pt/C dispersed on carbon paper (CP), while the CO₂RR was carried out on CuBiO₄/CP and CuBiO₄/CuO/CP in the presence of solar light. Half-cell measurements demonstrate the photoactivity of CuBiO₄/CuO/CP and CuBiO₄/CP electrodes for the CO₂RR under light exposure at low onset potential in a neutral pH solution, generating a positive theoretical open-circuit voltage of 0.89-0.91 V when coupled to glycerol electrooxidation in an alkaline medium. The use of the mixed medium in the membraneless system equipped with the photosensitive catalysts allowed the building of this galvanic cell. However, the feasibility of using CuBiO₄/CP is hindered by the disruption of the colaminar channel caused by hydrogen bubbles produced during concurrent water splitting. In contrast, the μPFC equipped with a CuBiO₄/CuO/CP photocathode demonstrates a stable and reproducible performance, delivering a maximum power density of 0.9 mW cm^-2. The formation of the CuBiO₄/CuO heterojunction effectively suppresses photocatalytic water splitting, allowing for efficient CO₂ conversion without disruption of the laminar flow channel. This innovative approach highlights the potential of μPFCs as sustainable energy converters for the utilization of CO₂ in aqueous solutions, offering a pathway toward carbon-neutral energy production.