A computational investigation into nickel-bis(diselenolene) complexes as potential catalysts for reduction of H+ to H2

Abstract

As a result of burning fossil fuels, levels of greenhouse gases in our atmosphere are increasing at an alarming rate. Such an increase in greenhouse gases threatens our planet due to global climate change. To reduce the production of greenhouse gases, we must switch from fossil fuels to alternative fuels for energy. The most viable alternative energy source involves the conversion of solar energy into chemical energy via the photocatalytic splitting of water to form molecular hydrogen. In the present work, the Ni-bis(1,2-diamine-diselenolene) and Ni-bis(1,2-dicyano-diselenolene) complexes were studied using density functional theory (DFT). From the results, it was found that the 1,2-diamine-diselenolene and 1,2-dicyano-diselenolene nickel complexes catalyze the formation of H2(g) with overall reaction Gibbs energies of +8.7 kJ mol–1 and +8.4 kJ mol–1, respectively, in a dilute aqueous environment versus the standard hydrogen electrode (SHE). Although both are able to catalyze the HER through a marginally endergonic reaction, the most thermodynamically favourable pathways differed between the complexes. In particular, the most thermodynamically favourable pathway for the formation of H2 by CNOx involves an EECC mechanism, whereas for NH2Ox, the most thermodynamically favourable pathway occurs via an ECCE mechanism. From the results presented, the choice of substituent on the alkene backbone significantly affects the reduction potential and reaction Gibbs energies of protonation. The considerably more positive reduction potential for the CN complexes may offer a solution to the problems experimentally observed for the production of H2.