Performance Analysis of Polymer Electrolyte Membrane Water Electrolyzer Using OpenFOAM®: Two-Phase Flow Regime, Electrochemical Model

Efficient and Stable Proton Exchange Membrane Water Electrolysis Enabled by Stress Optimization

Proton exchange membrane water electrolysis (PEMWE) is a promising solution for the conversion and storage of fluctuating renewable energy sources. Although tremendously efficient materials have been developed, commercial PEMWE products still cannot fulfill industrial demands regarding efficiency and stability. In this work, we demonstrate that the stress distribution, a purely mechanical parameter in electrolyzer assembly, plays a critical role in overall efficiency and stability. The conventional cell structure, which usually adopts a serpentine flow channel (S-FC) to deliver and distribute reactants and products, resulted in highly uneven stress distribution. Consequently, the anode catalyst layer (ACL) under the high stress region was severely deformed, whereas the low stress region was not as active due to poor electrical contact. To address these issues, we proposed a Ti mesh flow channel (TM-FC) with gradient pores to reduce the stress inhomogeneity. Consequently, the ACL with TM-FC exhibited 27 mV lower voltage initially and an 8-fold reduction in voltage degradation rate compared to that with S-FC at 2.0 A/cm2. Additionally, the applicability of the TM-FC was demonstrated in cross-scale electrolyzers up to 100 kW, showing a voltage increase of only 20 mV (accounting for less than 2% of overall voltage) after three orders of magnitude scaleup.

Advances in Selective Electrochemical Oxidation of 5-Hydroxymethylfurfural to Produce High-Value Chemicals

The conversion of biomass is a favorable alternative to the fossil energy route to solve the energy crisis and environmental pollution. As one of the most versatile platform compounds, 5-hydroxymethylfural (HMF) can be transformed to various value-added chemicals via electrolysis combining with renewable energy. Here, the recent advances in electrochemical oxidation of HMF, from reaction mechanism to reactor design are reviewed. First, the reaction mechanism and pathway are summarized systematically. Second, the parameters easy to be ignored are emphasized and discussed. Then, the electrocatalysts are reviewed comprehensively for different products and the reactors are introduced. Finally, future efforts on exploring reaction mechanism, electrocatalysts, and reactor are prospected. This review provides a deeper understanding of mechanism for electrochemical oxidation of HMF, the design of electrocatalyst and reactor, which is expected to promote the economical and efficient electrochemical conversion of biomass for industrial applications.

Effect of Gravity and Various Operating Conditions on Proton Exchange Membrane Water Electrolysis Cell Performance

Water electrolysis is an eco-friendly method for the utilization of renewable energy sources which provide intermittent power supply. Proton exchange membrane water electrolysis (PEMWE) has a high efficiency in this regard. However, the two-phase flow of water and oxygen at the anode side causes performance degradation, and various operating conditions affect the performance of PEMWE. In this study, the effects of four control parameters (operating temperature, flow rate, cell orientation, and pattern of the channel) on the performance of PEMWE were investigated. The effects of the operating conditions on its performance were examined using a 25 cm² single-cell. Evaluation tests were conducted using in situ methods such as polarization curves and electrochemical impedance spectroscopy. The results demonstrated that a high operating temperature and low flow rate reduce the activation and ohmic losses, and thereby enhance the performance of PEMWE. Additionally, the cell orientation affects the performance of PEMWE owing to the variation in the two-phase flow regime. It was observed that the slope of specific sections in the polarization curve rapidly increases at a specific cell voltage.

Model-Based Analysis of Low Stoichiometry Operation in Proton Exchange Membrane Water Electrolysis

Proton exchange membrane water electrolysis cells are typically operated with high water flow rates in order to guarantee the feed supply for the reaction, the hydration of the ionomer phase and to homogenize the temperature distribution. However, the influence of low flow rates on the cell behavior and the cell performance cannot be fully explained. In this work, we developed a simple 1+1-dimensional mathematical model to analyze the cell polarization, current density distribution and the water flow paths inside a cell under low stoichiometry condition. The model analysis is in strong context to previous experimental findings on low water stoichiometry operations. The presented analysis shows that the low water stoichiometry can lead to dry-out at the outlet region of the anode channel, while a water splitting reaction is also present there. The simulation results show that the supply with water in this region is achieved by a net water transport from the cathode to the anode catalyst layer resulting in higher local proton resistances in the membrane and the anode catalyst layer.