Abstract:We have developed ah ighly active nanostructured iridium catalyst for anodes of proton exchange membrane (PEM) electrolysis.C lusters of nanosized crystallites are obtained by reducing surfactant-stabilized IrCl 3 in water-free conditions.T he catalyst shows af ive-fold higher activity towards oxygen evolution reaction (OER) than commercial Ir-black. The improved kinetics of the catalyst are reflected in the high performance of the PEM electrolyzer (1 mg Ir cm À2 ), showing an unparalleled low overpotential and negligible degradation. Our results demonstrate that this enhancement cannot be only attributed to increased surface area, but rather to the ligand effect and low coordinate sites resulting in ahigh turnover frequency (TOF). The catalyst developed herein sets ab enchmark and as trategy for the development of ultra-low loading catalyst layers for PEM electrolysis.

Fourier transform infrared absorption spectroscopy and temperature programmed desorption have been used to study the reactions of methanol (CH3OH, CD3OH and CH3 18OH) on the clean Ru(0001) surface in the temperature range 80−600 K. It has been found that the methanol thermal evolution is initiated by a breaking of the OH bond, forming an upright (C 3v symmetry) methoxy species (CH3O). This reaction requires annealing to about 180 K and, for dense layers, proceeds in parallel to molecular desorption. At 220 K, methoxy is found to be the dominant surface species. However, its decomposition into CO + 3H already starts at this temperature, as deduced from the appearance of the ν(CO) mode of CO; that is, methoxy is stable in a narrow temperature range only. Yet, CH3O formed at 220 K can be stabilized up to 320−340 K by means of surface site blocking through CO coadsorption. Hydrogen and carbon monoxide, the resulting reaction products from methoxy decomposition, desorb at 330−350 and 470 K, respectively. No other reaction intermediates have been identified. An entirely new interpretation is presented regarding the production of water detected in thermal desorption at about 190 K. On the basis of experiments with different methanol and oxygen isotopes, we demonstrate that it is the hydrogen of the hydroxyl group of methanol and residual surface oxygen (most likely at steps and a relict of the surface cleaning procedure with oxygen) which contributes to the formation of water. As intermixing of abstracted hydrogen with coadsorbed deuterium is found to be negligible, the hydrogen abstracted from methanol is suggested to react directly with surface oxygen, that is, without adsorbing on the surface in between. CO bond breaking, long believed to act as the primary reaction step toward water formation, can definitely be ruled out.

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Cost reduction and high efficiency are the mayor challenges for sustainable H2 production via proton exchange membrane (PEM) electrolysis. Titanium-based components such as bipolar plates (BPP) have the largest contribution to the capital cost. This work proposes the use of stainless steel BPPs coated with Nb and Ti by magnetron sputtering physical vapor deposition (PVD) and vacuum plasma spraying (VPS), respectively. The physical properties of the coatings are thoroughly characterized by scanning electron, atomic force microscopies (SEM, AFM); and X-ray diffraction, photoelectron spectroscopies (XRD, XPS). The Ti coating (50 μm) protects the stainless steel substrate against corrosion, while a 50-fold thinner layer of Nb decreases the contact resistance by almost one order of magnitude. The Nb/Ti-coated stainless steel bipolar BPPs endure the harsh environment of the anode for more than 1000 h of operation under nominal conditions, showing a potential use in PEM electrolyzers for large-scale H2 production from renewables.

Hydrogen produced by water splitting is a promising solution for a sustained economy from renewable energy sources. Proton exchange membrane (PEM) electrolysis is the utmost suitable technology for this purpose, although the quest for low cost, highly active and durable catalysts is persistent. Here we develop a nanostructured iridium catalyst after electrochemically leaching ruthenium from metallic iridium-ruthenium, Ir 0.7 Ru 0.3 O x (EC), and compare its physical and electrochemical properties to the thermally treated counterpart: Ir 0.7 Ru 0.3 O 2 (TT). Ir 0.7 Ru 0.3 O x (EC) shows an unparalleled 13-fold higher oxygen evolution reaction (OER) activity compared to the Ir 0.7 Ru 0.3 O 2 (TT). PEM electrolyzer tests at 1 A cm-2 show no increase of cell voltage for almost 400 h, proving that Ir 0.7 Ru 0.3 O x (EC) is one of the most efficient anodes so far developed.