Fe-modified porous biochar derived from tea waste as a high-performance catalyst for oxygen evolution reaction in water splitting
Raquel Domínguez-Alonso, M.Á. Sanromán, Marta Pazos, Aida M. Díez
Abstract
Slow water splitting reaction kinetic highly depends on the oxygen evolution reaction (OER), needing further optimization to improve hydrogen production. This study presents, for the first time, a noble metal-free catalyst comprising black tea biochar modified with iron, resulting in a new and environmentally friendly composite which is useful for water splitting applications. Different percentages of added Fe were studied, showing that this parameter is critical for attaining good electrochemical activity. The goal was to find a balance between catalyst loading and surface-active sites blockage. 10 % of Fe content (Fe-BTbio10) emerged as the most effective catalyst due to its considerable OER performance, defeating the benchmark catalyst IrO 2 . Catalyst loading was also optimized, requiring a low overpotential for activated Fe-BTbio10 of 354.86, 395.27 and 405.94 mV for obtaining 10, 50 and 100 mA cm −2 , respectively, and a Tafel slope value of 44.9 mV dec −1 for a dosage of 0.25 mg cm −1 . The effect of pH and hydrogen evolution reaction (HER) were also assessed, demonstrating that this catalyst is more suitable for alkaline OER. An in depth characterisation explained the material's excellent performance, based on functional groups presence and Fe linkage. The catalyst showed a notably competitive stability, defeating IrO 2 and supporting this circular economy approach. • Fe-modified black tea biochar was successfully synthesized, aiming circular economy. • The Fe-BTbio10 catalyst defeated IrO 2 in both performance and stability for the OER. • The Fe quantity added to the biochar significantly influences the OER process. • Noble-metal free catalysts have a promising potential to increase OER performance. • A full characterization prior and after use of the novel Fe-BTbio10 was conducted.