Metal-free (B, N, P)-doped ordered mesoporous carbons for enhanced electrocatalytic oxidation of phenol

Metal-free (B, N, P)-doped ordered mesoporous carbons are an interesting novel class of materials that circumvent the use of critical raw materials and are characterised by an ordered nanostructure that allows for the exploration of concepts such as nanoconfinement and 3D-like nanostructure in electrodes for electrocatalytic processes. In particular, a valuable novel direction is their use for the selective electrocatalytic oxidation (ECO) of waste products to higher-added-value chemicals rather than their conversion to CO2, as studied today. We focused the investigation on phenol, a main component that is resistant to biodegradation in many industrial wastewater streams. Additionally, it serves as a model for utilising the phenol derivatives produced during lignin depolymerisation. This study investigates the selective ECO of phenol to p-benzoquinone (BQ), a key industrial intermediate, using metal-free ordered mesoporous carbons (OMCs) synthesised via SBA-15 silica templates. OMCs were doped with boron, nitrogen, and phosphorus to tune their electronic properties and active sites, thereby enhancing their electrocatalytic performance. Characterisation revealed high surface areas (up to 1000 m2/g) and a well-defined mesoporous structure. Electrochemical tests conducted in a microflow cell confirmed the effectiveness of the synthesised materials as anodes for the electrocatalytic conversion of phenol into value-added products. Among them, phosphorus-doped ordered mesoporous carbons (P@OMCs) demonstrated outstanding performance, achieving phenol conversions of up to 50 % and benzoquinone (BQ) selectivity of 40 %. These values significantly surpass those obtained with commercial conductive carbon black (Ketjen black) and boron-doped graphene (BDG), which showed phenol conversion and BQ selectivity below 40 % and 25 %, respectively. The superior performance of P@OMC correlates with its lowest Tafel slope, indicating reduced mass transport limitations and enhanced reaction kinetics. Furthermore, P@OMC exhibited the highest electrochemical surface area (ECSA), suggesting a greater density of accessible electrocatalytic active sites. These findings highlight the strong potential of heteroatom-doped OMCs as effective and sustainable electrocatalysts for phenol upgrading, offering a viable route towards scalable and environmentally friendly biomass conversion technologies.