Catalyst Self-Assembly Accelerates Bimetallic Light-Driven Electrocatalytic H2 Evolution in Water

Hydrogen evolution is an important fuel-generating reaction that has been subject to mechanistic debate about the roles of monometallic and bimetallic pathways. In this study, molecular iridium catalysts that undergo photoelectrochemical dihydrogen evolution afford a rare opportunity to systematically understand the factors that promote bimetallic H–H coupling. Covalently tethered diiridium catalysts evolve H2 from neutral water faster than monometallic catalysts, even at lower overpotential. The origin of this improvement is noncovalent supramolecular self-assembly into “all-catalyst” nanoscale aggregates that efficiently harvest light and form H–H bonds. New monometallic catalysts containing long-chain alkane substituents leverage the self-assemly to evolve H2 from neutral water close to the expected maximum rate for a light-driven water splitting reaction and with activity even below 100 mV overpotential. Design parameters for holding multiple catalytic sites in close proximity and tuning catalyst microenvironment emerge from this work.