Developing high-performance catalytic electrodes for on-site hydrogen peroxide electrosynthesis

Hydrogen peroxide (H₂O₂) is a versatile oxidant, but its production heavily depends on the energy-intensive anthraquinone process. H₂O₂ electrosynthesis via a two-electron oxygen reduction reaction (2e^- ORR) can be proceeded with renewable electricity under mild conditions, satisfying the pursuit of green chemistry for a sustainable future. Notably, H₂O₂ produced in acidic media with potent oxidative properties performs the best for downstream applications. However, there is a limited choice of electrodes to enable acidic H₂O₂ electrosynthesis without relying on catalysts based on noble metals. This thesis aims to overcome this limitation by rationally designing and fabricating electrodes with carbon-based catalysts.

The research begins by developing a 2e^- ORR electrode composed of atomic cobalt-decorated vertical graphene (VG). This electrode exhibits a hierarchical structure that exposes the active sites and maximises their utilisation while also ensuring electrode mass transport efficiencies. It enables the most energy-efficient, rapid acidic H₂O₂ production in a flow cell, demonstrating the possibility of decoupling 2e^- ORR from high-cost catalytic electrodes.

Along this line, an enhanced fabrication strategy is devised for three-dimensional cobalt-containing electrodes by impregnating VG into a zeolitic imidazolate framework-67 precursor followed by low-temperature sintering. The resulting electrode features a unique film-on-graphene configuration, exhibiting high activity, nearly 100% selectivity, and prolonged stability for acidic H₂O₂ electrosynthesis. The critical mechanism behind its fabrication process is also carefully studied to inform the development of desirable 2e^- ORR electrodes.

Furthermore, a metal-free carbon electrode with bifunctional capabilities is developed by annealing a polymer coating on VG. This electrode not only works well in acidic H2O2 production, comparable to the metal-containing electrodes reported in earlier chapters, but also exhibits the ability to catalyse the active OH· radical generation from the H₂O₂ produced, leading to efficient oxidation synthesis of a high-value chemical of peracetic acid. Such a bifunctionality enriches the context of on-site H₂O₂ electrosynthesis from efficient production to utilisation.

Overall, this thesis highlights the potential of precious metal-free electrodes for H₂O₂ electrosynthesis, providing new insights for the electrification of the chemical industry towards a sustainable future.