A H2O2 PEM Electrolyser with Continuous Online Spectrophotometric Product Detection: Load Flexibility Studies

Abstract

Hydrogen peroxide (H2O2) is a commodity chemical with an increasing annual worldwide demand. The green oxidant is widely used in various fields, including pulp and paper bleaching industry, chemical synthesis, and wastewater treatment. H2O2 is commonly produced by the industrial anthraquinone process, which suffers from high energy consumption and the generation of a variety of undesirable by-products [1]. The electrochemical production of H2O2 via the two-electron oxygen reduction reaction is a promising approach for the replacement of the industrial anthraquinone process, yet it is not able to compete economically. However, the electrochemical H2O2 production opens the possibility to produce hydrogen peroxide using renewable energies. Naturally, green energy sources underlie fluctuations regarding the accessible power, resulting in a fluctuating energy market. Being able to respond to the energy market with increasing or decreasing the load of an electrochemical unit can offer a significant economic value. This economic advantage can help to bridge the gap between the production costs for hydrogen peroxide produced by renewable energies and by the state-of-the-art industrial anthraquinone process. Due to a limited time resolution, classical off-line characterisation techniques for the detection of H2O2 are not suitable to investigate the influence of dynamic conditions upon the H2O2 production rates.Here we present a novel on-line analysis setup based on the spectrophotometric analysis with titanium oxalate [2], which allows the determination of hydrogen peroxide continuously at the moment it is formed. For this purpose, we combined two mass flow controller, one continuously delivering the H2O2 containing electrolyte and the other delivering the titanium oxalate solution. Both solutions were mixed in a subsequent micromixer and pumped though a spectrophotometric flow cell, where the absorbance of the resulting pertitanic acid is recorded and the corresponding H2O2 concentration is calculated. Therefore, with our setup, the concentration of H2O2 can be continuously measured and the influence of varying process parameter can be directly monitored. We validated the setup with load flexibility experiments, where current load steps above and below a reference load were performed and the resulting Faraday efficiencies and production rates within an electrolyser were monitored.