The Electrocatalytic Evolution of Oxygen and Hydrogen by Cobalt and Nickel Compounds.

摘要

In order to meet the ever-increasing demand for energy, a worldwide transition away from fossil fuels to renewable solar--fuels is required. However, the intermittency of local insolation mandates a cost-effective and efficient storage scheme. Using solar-derived electricity to drive the thermodynamically uphill water splitting reaction to generate dihydrogen and dioxygen is one promising method of storing solar energy in fuels.;This "artificial photosynthesis" scheme requires the execution of two half-reactions, one involving the oxidation of water to O2---the oxygen evolution reaction (OER)---and the other entailing the reduction of hydrogen ions to H2---the hydrogen evolution reaction (HER). Accomplishing these electrocatalytic reactions stresses the development of catalysts that are capable of mediating reactions that are in net multi-electron, multi-proton transformations.;Transition metal oxides are known to be promising candidates for mediating the OER and their electrocatalytic properties have been studied extensively and optimized for operation at pH extremes. In contrast, intermediate pH OER has been relatively underexplored and the influence of proton-coupled electron transfer (PCET) reactions on OER kinetics of these materials at close-to-neutral pH has for long remained unclear. The OER studies described here have focused on elucidating the underlying mechanistic basis for the catalytic behavior of a class of structurally disordered first-row transition metal oxides, with an emphasis on intermediate-pH catalysis and proton--electron coupling.;At a fundamental level, understanding how protons and electrons may be managed and coupled to engender improved activity remains of great importance to the design of new electrocatalysts. To this end, the synthesis and study of homogeneous HER catalysts bearing functional groups in the second coordination sphere that can modulate proton--electron coupling is particularly interesting. The HER studies presented here discuss this important issue within the context of metalloporphyrin catalysts possessing proton relays.