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AIRInternational audienc

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In this paper, we explore the drastic differences in transport properties and catalytic activities for two structural polymorphs of NiP 2 : cubic (Pa3; No. 205) and monoclinic NiP 2 (C2/c; No. 15). The former one has been long assumed to be the high-pressure metastable phase, as it had been originally synthesized through high-pressure methods. Synthetic and in situ synchrotron X-ray diffraction studies unambiguously show that the cubic polymorph can be synthesized at ambient pressure but irreversibly transforms into the monoclinic structure above 876 K. Band structure calculations and transport measurements show that cubic NiP 2 is a semimetal, while the monoclinic polymorph is an ntype direct band gap semiconductor. Both compounds exhibit low thermal conductivities, with cubic NiP 2 exhibiting a value of 1.7 W•m −1 K −1 at 300 K. The bulk structure of the phosphides may affect the surface-related properties. Unlike the monoclinic polymorph, cubic NiP 2 excels in both half-cell HER and OER measurements. In alkaline half-cell OER, cubic NiP 2 outperforms the RuO 2 standard. More importantly, HER tests in a PEM electrolysis single cell showed high promise for cubic NiP 2 , which requires only 13% higher overpotentials when compared to state-of-the-art Pt/IrRuO x -based assemblies, far surpassing any reported properties of metal pnictide or chalcogenide full cells.

This study investigates the production of hydrogen from the electrochemical reforming of short-chain alcohols (methanol, ethanol, iso-propanol) and their mixtures. High surface gas diffusion Pt/C electrodes were interfaced to a Nafion polymeric membrane. The assembly separated the two chambers of an electrochemical reactor, which were filled with anolyte (alcohol+H2O or alcohol+H2SO4) and catholyte (H2SO4) aqueous solutions. The half-reactions, which take place upon polarization, are the alcohol electrooxidation and the hydrogen evolution reaction at the anode and cathode, respectively. A standard Ag/AgCl reference electrode was introduced for monitoring the individual anodic and cathodic overpotentials. Our results show that roughly 75% of the total potential losses are due to sluggish kinetics of the alcohol electrooxidation reaction. Anodic overpotential becomes larger as the number of C-atoms in the alcohol increases, while a slight dependence on the pH was observed upon changing the acidity of the anolyte solution. In the case of alcohol mixtures, it is the largest alcohol that dictates the overall cell performance.

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The main applications of yttria stabilized zirconia in catalysis are briefly reviewed and analyzed based on its functionalities.

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