Pulsed-Current Operation Enhances H2O2 Production on a Boron-Doped Diamond Mesh Anode in a Zero-Gap PEM Electrolyzer

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) induced by pulsed electrolysis. A low electrolyte flow rate (V & sdot;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, 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 & sdot;anolyte of 0.75 cm3 min-1, resulted in the best performance. This adjustment increased the FEH2O2 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.