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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.

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We investigated the reduction process of sulfur during cycling in a lithium−sulfur battery, correlating the output of ultraviolet−visible (UV−vis) spectroscopy and further characterization techniques with a theoretical model. The experimental setup allows carrying out UV−vis absorption measurements under argon atmosphere. The characteristic absorption bands (λ max ) of sulfur and dilithium sulfide dissolved in tetra-ethylene glycol dimethyl ether (TEGDME) are determined to be at 265 and 255 nm, respectively. Reference solutions of polysulfides diminish the λ max in the UV region with decrease of polysulfide order. The same tendency is observed in the range between 25−75% depth of discharge (DOD), caused by a progressive reduction of polysulfides in the electrolyte. At 425 and 615 nm, absorption bands are identified in the reference polysulfide solutions and also in the electrolyte at different DOD. These bands are interpreted as the characteristic bands of S 4 2− and S 3•−, and concentration changes of these species are determined semiquantitatively. The highest concentration of polysulfides is found at around 37% DOD (450 Ah•kg S −1 ). This was confirmed by the results of electrochemical impedance spectroscopy and computer simulations.

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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.

The capacity fading of lithium/sulfur (Li/S) cells is one major challenge that has to be overcome for a successful commercialization of this electrochemical storage system. Therefore it is essential to detect the major fading mechanisms for further improvements of this system. In this work, the processes leading to fading are analyzed in terms of a linear four state model and correlated to the distribution of relaxation times calculated with a modified Levenberg-Marquardt algorithm. Additionally, the Warburg impedance and the solution resistance are also obtained by the same algorithm. The detailed analysis of intermediate states during the first cycle gives the distinction between relaxation processes at the sulfur cathode and at the lithium anode. The influence of the polysulfides on the impedance parameters was evaluated using symmetric cells; this yields a good correlation with the results obtained from the first discharge/charge experiment. A fast and a slow capacity fading process are observed for the charge and the discharge during 50 cycles. The fast fading process can be assigned to Faradaic reactions at the lithium anode.