Pulsed-Current Operation Enhances H<sub>2</sub>O<sub>2</sub> Production on a Boron-Doped Diamond Mesh Anode in a Zero-Gap PEM Electrolyzer.

Abstract

A niobium (Nb) mesh electrode was coated with boron-doped diamond (BDD) using chemical vapor deposition in a custom-built hot-filament reactor. The BDD-functionalized mesh was tested in a zero-gap electrolysis configuration and evaluated for the anodic formation of H₂O₂ by selective oxidation of water, including the analysis of the effects on Faradaic efficiency towards H₂O₂ FEH2O2${\left( {{\rm{FE}}_{{\rm{H}}_2 {\rm{O}}_2 } } \right)}$ induced by pulsed electrolysis. A low electrolyte flow rate ( V˙anolyte${{\dot {\rm V}}_{{\rm{anolyte}}} }$ ) was found to result in a relatively high concentration of H₂O₂ in single-pass electrolysis experiments. Regarding pulsed electrolysis, we show an optimal ratio of on-time to off-time to obtain the highest concentration of H₂O₂. Off-times that are "too short" result in decreased FEH2O2${{\rm{FE}}_{{\rm{H}}_2 {\rm{O}}_2 } }$ , whereas "too long" off-times dilute the product in the electrolyte stream. Using our electrolyzer setup with an anodic pulse of 2 s with 4 s intervals, and a V˙anolyte${{\dot {\rm V}}_{{\rm{anolyte}}} }$ of 0.75 cm³ min^-1, resulted in the best performance. This adjustment increased the FEH2O2${{\rm{FE}}_{{\rm{H}}_2 {\rm{O}}_2 } }$ by 70 % compared to constant current electrolysis, at industrially relevant current densities (150 mA cm^-2). Fine tuning of BDD morphology, flow patterns, and anolyte composition might further increase the performance of zero-gap electrolyzers in pulsed operation modes.