PNNL

Abstract

A nickel bis(diphosphine) complex containing proton relays in the second and outer coordination spheres, Ni(PCy2N(CH2)2OMe)2, (PCy2N(CH2)2OMe = 1,5-di(methoxyethyl)-3,7-dicy?clohexyl-1,5-diaza-3,7-diphosphacyclooctane), is an electrocatalyst for hydrogen oxidation. The addition of hydrogen to? the Ni(II) complex results in rapid formation of three isomers of the doubly protonated ?Ni(0) complex, [Ni(PCy2N(CH2)2OMe2H)2]2+. The three isomers show fast intramolecular interconversion at 40 °C, unique to this complex in this class of catalysts. Under conditions of 1.0 atm H2 using H2O as a base, catalytic oxidation proceeds at a turnover frequency of 5 s-1 and an overpotential of 720 mV, as determined from the potential at half of the catalytic current. Compared to the previously reported Ni(PCy2NBn)2 complex, the new complex operates at a faster rate and at a lower overpotential. The results of this study indicate that the presence of the pendant methoxy group in the outer coordination sphere of the catalyst plays a key role, facilitating intramolecular proton movement prior to intermolecular proton removal required to complete the catalytic cycle. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.