Overall Design of Anode with Gradient Ordered Structure with Low Iridium Loading for Proton Exchange Membrane Water Electrolysis

Abstract

Insufficient catalyst utilization, limited mass transport, and high ohmic resistance of the conventional membrane electrode assembly (MEA) lead to significant performance losses of proton exchange membrane water electrolysis (PEMWE). Herein we propose a novel ordered MEA based on anode with a 3D membrane/catalytic layer (CL) interface and gradient tapered arrays by the nanoimprinting method, confirmed by energy dispersive spectroscopy. Benefiting from the maximized triple-phase interface, rapid mass transport, and gradient CL by overall design, such an ordered structure with Ir loading of 0.2 mg cm–2 not only greatly increases the electrochemical active area by 4.2 times but also decreases the overpotentials of both mass transport and ohmic polarization by 13.9% and 8.7%, respectively, compared with conventional MEA with an Ir loading of 2 mg cm–2, thus ensuring a superior performance (1.801 V at 2 A cm–2) and good stability. This work provides a new strategy of designing MEA for high-performance PEMWE.

Key components and design strategy of the membrane electrode assembly for alkaline water electrolysis

“…26i, by using gradient tapered anode arrays and a 3D CL/PEM interface, Dong et al proposed an ordered MEA for PEMWE. 332 As shown in Fig. 26j and k, compared to a 2D CL/PEM interface and relatively tortuous pore structures, the anode with gradient tapered arrays displays a 3D CL/PEM interface, which could offer continuous triple-phase transfer pathways at CLs and interfaces.…”

Ordered Membrane Electrode Assembly with Drastically Enhanced Proton and Mass Transport for Proton Exchange Membrane Water Electrolysis

“…In particular, the stacking structure of plentiful Ir catalysts in MEA-without array formed plentiful tortuous porosity, which increases both the gas and water transport resistance, especially at high current densities, thus leading to a significant improvement of cell voltage. In comparison with the MEA-column array (2260 mA cm –2 ), a higher current density for MEA-cone array is attributed to the gradient distribution of the Nafion content of cone Nafion array, which endows a more efficient proton transfer in MEA-cone array. , …”

“…Furthermore, a slightly increased ohmic resistance in MEA-column array than that of MEA-without array can be attributed to the increase of Nafion membrane thickness. It is noted that MEA-cone array shows the lowest ohmic resistance compared to those of MEA-column array and MEA-without array, suggesting that a cone array with a gradient structure is beneficial to facilitating proton transfer in MEA. , …”

“…In this regard, an ordered Nafion array with the direction perpendicular to bulk membrane has been developed in a recent report. 17 As presented in Scheme 1d, this ordered array not only provides plentiful fast channels for proton transfer by high density and cone structure but also significantly improves the utilization of catalyst and thus brings significant performance improvement of MEA. Furthermore, PEM electrolyzer was generally operated at high current densities to generate a commercially competitive rate; however, high operational current is a huge challenge for mass transfer, 18 especially in the case of ultralow Ir loading.…”

“…The improvement of the proton transfer channel is more likely to bring significant enhancement of PEMWE performance in theory. In this regard, an ordered Nafion array with the direction perpendicular to bulk membrane has been developed in a recent report . As presented in Scheme d, this ordered array not only provides plentiful fast channels for proton transfer by high density and cone structure but also significantly improves the utilization of catalyst and thus brings significant performance improvement of MEA.…”