Comprehensive Analysis of the Gradient Porous Transport Layer for the Proton-Exchange Membrane Electrolyzer.

A reasonable porous transport layer (PTL) is crucial to decreasing the mass-transfer loss in proton-exchange membrane water electrolyzers (PEMWEs). In this study, it was experimentally demonstrated that the gradient porosity PTL is beneficial in improving the performance of electrolyzers. The research comprehensively investigates the impact of gradient porosity PTL structures on the performance of the PEMWE, considering mass transfer and interfacial contact. It offers insights into the two-phase (oxygen-water) flow transport mechanisms within the PTLs using a 2D numerical model based on the actual PTL geometry. At the microscopic level, it analyzes how the interfacial contact impacts proton and electron transport mechanisms, affecting not only the contact resistance but also the number of effective catalytic sites for the oxygen evolution reaction. Experimental results demonstrate that the cis-gradient porosity PTL leads to a performance enhancement of 9.3% at 2.2 A/cm2. Numerical simulations reveal that the drivers of oxygen transport include the surface tension of the fibers and the pressure drop influenced by the local PTL porosity. Further analysis indicates that the lower oxygen saturation in the bottom region of the PTL with cis-gradient porosity favors a lower oxygen coverage area in the catalyst layers (CL) since the narrower pore space and higher capillary pressure increase the number of water flow paths into the CL. Overall, this study provides valuable insights for designing high-performance PTLs for use in electrolyzers.

Optimization method for capacity configuration and power allocation of electrolyzer array in off-grid integrated energy system.

Hydrogen production using renewable energy is in line with China's the goal of carbon peak and carbon neutrality. The construction of off-grid hydrogen energy industrial park can effectively achieve local utilization of renewable energy and develop the green hydrogen industry. However, off-grid hydrogen energy industrial park has not the compensation and sustentation from large power grid, the stable operation and economic production of electrolyzer are affected by significant factors, such as power fluctuation and frequent start stop. Therefore, this paper proposed the optimization method for capacity configuration and power allocation of electrolyzer array in off-grid integrated energy system. Firstly, based on units of energy supply, energy conversion, and energy storage, a structural model of off-grid integrated energy system was established. Then, by analyzing the operational characteristics of single electrolyzer and electrolyzer array, flexible mode of multiple electrolyzers operating in combination was proposed. Furthermore, considering the hydrogen production cost, the mean of hydrogen production volatility and penalty cost, the capacity configuration and power allocation methods for electrolyzer array were proposed, and the optimization problem is solved with multi-objective particle swarm optimization algorithm. Finally, the hydrogen energy industrial park in Zhangye is taken as example to verify the effectiveness of above research content. Compared to a single type of alkaline electrolyzer, the mean of hydrogen production volatility of multiple electrolyzers operating in combination has decreased by 43.2 %, the hydrogen production quantity has increased by 9.74 %. Compared to a single type of proton exchange membrane electrolyzer, the hydrogen production cost has been reduced by 14.16 %. Compared with the balanced running mode, the flexible operation mode can improve the cost-effective and quantity of hydrogen production.

Integration of geothermal-driven organic Rankine cycle with a proton exchange membrane electrolyzer for the production of green hydrogen and electricity.

Engineers and scientists are increasingly interested in clean energy options to replace fossil fuels in response to rising environmental concerns and dwindling fossil fuel resources. There has been an increase in the installation of renewable energy resources, and at the same time, conventional energy conversion systems have improved in efficiency. In this paper, several multi-generation systems based on geothermal energy are modeled, assessed, and optimized which employ an organic Rankine cycle and a proton-exchange membrane electrolyzer subsystem in five different configurations. Based on the results, the evaporator mass flow rate and inlet temperature, turbine efficiency, and inlet temperature are the most influential parameters on system outputs, namely, net output work, hydrogen production, energy efficiency, and cost rate. In this study, the city of Zanjan (Iran) is selected for a case study, and the results of system energy efficiency for changes in ambient temperature are examined during the four seasons of the year. To determine the optimal values of the objective functions, energy efficiency, and cost rate, NSGA-II multi-objective genetic algorithm is employed, and a Pareto chart is derived. The system's irreversibility and performance are gauged by energy and exergy analyses. At the optimum state, the best configuration yields an energy efficiency and cost rate of 0.65% and 17.40 $/h, respectively.

Oxygen Evolution Electrocatalysts for the Proton Exchange Membrane Electrolyzer: Challenges on Stability.

Hydrogen generated by proton exchange membrane (PEM) electrolyzer holds a promising potential to complement the traditional energy structure and achieve the global target of carbon neutrality for its efficient, clean, and sustainable nature. The acidic oxygen evolution reaction (OER), owing to its sluggish kinetic process, remains a bottleneck that dominates the efficiency of overall water splitting. Over the past few decades, tremendous efforts have been devoted to exploring OER activity, whereas most show unsatisfying stability to meet the demand for industrial application of PEM electrolyzer. In this review, systematic considerations of the origin and strategies based on OER stability challenges are focused on. Intrinsic deactivation of the material and the extrinsic balance of plant-induced destabilization are summarized. Accordingly, rational strategies for catalyst design including doping and leaching, support effect, coordination effect, strain engineering, phase and facet engineering are discussed for their contribution to the promoted OER stability. Moreover, advanced in situ/operando characterization techniques are put forward to shed light on the OER pathways as well as the structural evolution of the OER catalyst, giving insight into the deactivation mechanisms. Finally, outlooks toward future efforts on the development of long-term and practical electrocatalysts for the PEM electrolyzer are provided.

Exploring the Impacts of Conditioning on Proton Exchange Membrane Electrolyzers by In Situ Visualization and Electrochemistry Characterization.

For a proton exchange membrane electrolyzer cell (PEMEC), conditioning is an essential process to enhance its performance, reproducibility, and economic efficiency. To get more insights into conditioning, a PEMEC with Ir-coated gas diffusion electrode (IrGDE) was investigated by electrochemistry and in situ visualization characterization techniques. The changes of polarization curves, electrochemical impedance spectra (EIS), and bubble dynamics before and after conditioning are analyzed. The polarization curves show that the cell efficiency increased by 9.15% at 0.4 A/cm2, and the EIS and Tafel slope results indicate that both the ohmic and activation overpotential losses decrease after conditioning. The visualization of bubble formation unveils that the number of bubble sites increased greatly from 14 to 29 per pore after conditioning, at the same voltage of 1.6 V. Under the same current density of 0.2 A/cm2; the average bubble detachment size decreased obviously from 35 to 25 µm. The electrochemistry and visualization characterization results jointly unveiled the increase of reaction sites and the surface oxidation on the IrGDE during conditioning, which provides more insights into the conditioning and benefits for the future GDE design and optimization.

Stable Potential Windows for Long-Term Electrocatalysis by Manganese Oxides Under Acidic Conditions.

Efficient, earth-abundant, and acid-stable catalysts for the oxygen evolution reaction (OER) are missing pieces for the production of hydrogen via water electrolysis. Here, we report how the limitations on the stability of 3d-metal materials can be overcome by the spectroscopic identification of stable potential windows in which the OER can be catalyzed efficiently while simultaneously suppressing deactivation pathways. We demonstrate the benefits of this approach using gamma manganese oxide (γ-MnO2 ), which shows no signs of deactivation even after 8000 h of electrolysis at a pH of 2. This stability is vastly superior to existing acid-stable 3d-metal OER catalysts, but cannot be realized if there is a deviation as small as 50-mV from the stable potential window. A stable voltage efficiency of over 70 % in a polymer-electrolyte membrane (PEM) electrolyzer further verifies the availability of this approach and showcases how materials previously perceived to be unstable may have potential application for water electrolysis in an acidic environment.

Discovery of true electrochemical reactions for ultrahigh catalyst mass activity in water splitting.

Better understanding of true electrochemical reaction behaviors in electrochemical energy devices has long been desired. It has been assumed so far that the reactions occur across the entire catalyst layer (CL), which is designed and fabricated uniformly with catalysts, conductors of protons and electrons, and pathways for reactants and products. By introducing a state-of-the-art characterization system, a thin, highly tunable liquid/gas diffusion layer (LGDL), and an innovative design of electrochemical proton exchange membrane electrolyzer cells (PEMECs), the electrochemical reactions on both microspatial and microtemporal scales are revealed for the first time. Surprisingly, reactions occur only on the CL adjacent to good electrical conductors. On the basis of these findings, new CL fabrications on the novel LGDLs exhibit more than 50 times higher mass activity than conventional catalyst-coated membranes in PEMECs. This discovery presents an opportunity to enhance the multiphase interfacial effects, maximizing the use of the catalysts and significantly reducing the cost of these devices.