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The kinetically sluggish oxygen evolution reaction in proton exchange membrane water electrolyzers (PEMWEs) leads to high potentials of >1.5 V vs RHE at the anode electrode during operation. In contrast, an investigation with an in situ reference electrode indicates a much lower potential at the anode side of the bipolar plate which would allow the use of stainless steel and carbon as the bipolar plate materials. This decoupling is induced by the low conductivity of the circulating deionized water. In single cell electrolyzer tests, we show that carbon-coated 316L (C-316L) stainless steel is suitable as a bipolar plate material in contact with the anode and cathode sides of the PEMWE. The coating remains stable throughout the experiments, i.e., 720 h at the anode and 1000 h at the cathode side. Based on these results we regard carbon-coated stainless steel as a sustainable solution for the large-scale application of PEM water electrolysis since it might replace (Pt-coated) titanium in the bipolar plate.

Proton exchange membrane water electrolysis is a promising technology to produce green hydrogen from renewables, as it can efficiently achieve high current densities. Lowering iridium amount in oxygen evolution reaction electrocatalysts is critical for achieving cost-effective production of green hydrogen. In this work, we develop catalysts from Ir double perovskites. Sr 2 CaIrO 6 achieves 10 mA cm -2 at only 1.48 V. The surface of the perovskite reconstructs when immersed in an acidic electrolyte and during the first catalytic cycles, resulting in a stable surface conformed by short-range order edge-sharing IrO 6 octahedra arranged in an open structure responsible for the high performance. A proton exchange membrane water electrolysis cell is developed with Sr 2 CaIrO 6 as anode and low Ir loading (0.4 mg Ir cm -2 ). The cell achieves 2.40 V at 6 A cm -2 (overload) and no loss in performance at a constant 2 A cm -2 (nominal load). Thus, reducing Ir use without compromising efficiency and lifetime., (© 2022. The Author(s).)

For proton exchange membrane water electrolysis (PEMWE) to become competitive, the cost of stack components, such as bipolar plates (BPP), needs to be reduced. This can be achieved by using coated low-cost materials, such as copper as alternative to titanium. Herein we report on highly corrosion-resistant copper BPP coated with niobium. All investigated samples showed excellent corrosion resistance properties, with corrosion currents lower than 0.1 µA cm -2 in a simulated PEM electrolyzer environment at two different pH values. The physico-chemical properties of the Nb coatings are thoroughly characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). A 30 µm thick Nb coating fully protects the Cu against corrosion due to the formation of a passive oxide layer on its surface, predominantly composed of Nb 2 O 5 . The thickness of the passive oxide layer determined by both EIS and XPS is in the range of 10 nm. The results reported here demonstrate the effectiveness of Nb for protecting Cu against corrosion, opening the possibility to use it for the manufacturing of BPP for PEMWE. The latter was confirmed by its successful implementation in a single cell PEMWE based on hydraulic compression technology.