Converting Energy\nwith Glycerol and CO<sub>2</sub> in a Microfluidic Fuel Cell Equipped\nwith CuBiO<sub>4</sub>/CuO\nPhotocathode: Bypassing Bubbles Challenge of Concurrent Water Splitting

The imperative to address CO<sub>2</sub> emissions has\nprompted\nthe search for alternative approaches to capture this gas with minimal\nenergy consumption. In this context, leveraging the CO<sub>2</sub> reduction reaction (CO<sub>2</sub>RR) as an oxidant in fuel cells\nhas emerged as a sophisticated strategy to convert this gas into usable\nenergy. This study introduces a hybrid microfluidic photo fuel cell\n(μPFC) designed for the efficient conversion of CO<sub>2</sub> and glycerol into electrical energy. The prototype integrates 3D-printed\ncomponents with glass sealing, enabling precise control over the reactant\nflow and the use of light-sensitive catalysts. The anodic glycerol\nelectrooxidation was investigated on Pt/C dispersed on carbon paper\n(CP), while the CO<sub>2</sub>RR was carried out on CuBiO<sub>4</sub>/CP and CuBiO<sub>4</sub>/CuO/CP in the presence of solar light.\nHalf-cell measurements demonstrate the photoactivity of CuBiO<sub>4</sub>/CuO/CP and CuBiO<sub>4</sub>/CP electrodes for the CO<sub>2</sub>RR under light exposure at low onset potential in a neutral\npH solution, generating a positive theoretical open-circuit voltage\nof 0.89–0.91 V when coupled to glycerol electrooxidation in\nan alkaline medium. The use of the mixed medium in the membraneless\nsystem equipped with the photosensitive catalysts allowed the building\nof this galvanic cell. However, the feasibility of using CuBiO<sub>4</sub>/CP is hindered by the disruption of the colaminar channel\ncaused by hydrogen bubbles produced during concurrent water splitting.\nIn contrast, the μPFC equipped with a CuBiO<sub>4</sub>/CuO/CP\nphotocathode demonstrates a stable and reproducible performance, delivering\na maximum power density of 0.9 mW cm<sup>–2</sup>. The formation\nof the CuBiO<sub>4</sub>/CuO heterojunction effectively suppresses\nphotocatalytic water splitting, allowing for efficient CO<sub>2</sub> conversion without disruption of the laminar flow channel. This\ninnovative approach highlights the potential of μPFCs as sustainable\nenergy converters for the utilization of CO<sub>2</sub> in aqueous\nsolutions, offering a pathway toward carbon-neutral energy production.