Molecular Electrocatalysts
Molecular electrocatalysts are discrete coordination complexes, a metal center surrounded by designed ligands, that mediate electron transfer reactions at an electrode. Compared with extended solids such as metal oxides, they offer a way to tune reactivity through the ligand rather than through the composition of a bulk phase, which makes them a candidate route around limitations that apply to whole classes of solid catalysts. They can act in solution, driven by an electrode or a chemical oxidant, or be immobilized on a conducting support, where the support, binder and electrolyte also affect activity, selectivity and durability. See also Oxygen evolution reaction.
Immobilized iron TAML activator for water oxidation (2014)
Demeter and coworkers tested the prototype Fe(III) tetra-amido macrocyclic ligand (TAML) activator as an OER electrocatalyst. Dissolved in electrolyte it showed no electrocatalytic activity, but adsorbed on Vulcan carbon black and cast with Nafion onto glassy carbon or carbon paper it evolved O2 in 0.1 M HNO3, with an Fe(III)/Fe(IV) wave at 720 mV vs Ag/AgCl ahead of O2 onset near 1 V. At 5 mA on carbon paper it produced about 44 μmol O2 with an apparent Faradaic efficiency of about 45% (a lower bound) and an estimated upper-bound turnover frequency of 0.081 s-1, far above the earlier homogeneous system driven by ceric ammonium nitrate. FeCl3 and an iron porphyrin on the same support gave CO2 but no O2, so the activity was tied to the TAML ligand environment, not to iron alone (Demeter et al. 2014). Summary: demeter2014.
Machine learning data for transition metal complexes (2023)
Garrison and coworkers released tmQMwB97MV, 86,507 single-metal coordination complexes (30 transition metals, ligands built from 14 elements, 5 to 347 atoms) with ωB97M-V/def2-SVPD energies, as training data for surrogate models in homogeneous catalysis. They note that the set contains only closed-shell structures with charges of -1, 0 and +1 and no reactive intermediates, so it is not yet sufficient for screening catalysts through redox-rich reaction pathways (Garrison et al. 2023). Summary: garrison2023.