pH-differential design and operation of electrochemical and photoelectrochemical systems with bipolar membrane

Electrochemical and photoelectrochemical systems for hydrogen production and CO2 reduction are regarded as prospective technologies to achieve carbon-free energy vision. Electrolytes in different pH environment is desirable for each half electrochemical reaction to optimize the electrode kinetics and reduce the cost of noble metal catalysts. The bipolar membrane provides excellent opportunities to enable pH-differential operation. However, the effect of the bipolar membrane on electrochemical performance is not clarified yet. Here, a numerical modeling framework for bipolar membrane-based cells for electrochemical and photoelectrochemical applications was presented to study the viability of using bipolar membrane in the aspect of energy loss. The model for the first time successfully integrates the water dissociation at the bipolar membrane with the rest electrode kinetics and mass transfer, by treating the interfacial layer as a virtual electrode. Based on the model, the activation loss involved in the bipolar membrane devices were identified and compared with the ones with conventional monopolar membranes. A critical current density was identified for bipolar membranes, which is determined by the water dissociation performance of the membrane. Based on the critical current, the viable operation regions of using the bipolar membrane can be clarified for the electrochemical device. It is found that the bipolar membrane-based photoelectrochemical reactor has higher energy conversion efficiency than monopolar membrane configurations. However, the advantage of bipolar membrane becomes vanishing with photocurrent rising.