Stoichiometry-Controlled Synthesis of Nanoparticulate Mixed-Metal Oxyhydroxide Oxygen Evolving Catalysts by Electrochemistry in Aqueous Nanodroplets.

Mixed-metal oxyhydroxides-especially those of Ni and Fe-are one of the most active classes of materials known for catalyzing the oxygen evolution reaction (OER). Here, nanoparticulate mixed metal oxyhydroxides (of Ni, Fe, and Co) were prepared on an electrode surface by electrochemical reaction of a precursor solution encapsulated in aqueous nanodroplets (AnDs), with each of the droplets containing 10 s of attoliters of fluid. Electrode reactions and synthesis can be monitored in situ by electrochemistry as single AnD stochastically lands and interacts with the working electrode. Resultant metal oxyhydroxide nanoparticles can be size and composition controlled precisely by modulating the precursor solution stored in the AnD. Nanoparticulate metal oxyhydroxides were implemented as catalysts for the OER and exhibited superior catalysis compared to their thin-film counterparts, demonstrating a hundred-thousand-fold enhancement in atom efficiency at comparable turnover rates.

Surfactant-free electrochemical synthesis of metallic nanoparticles via stochastic collisions of aqueous nanodroplet reactors.

Stochastic collisions of aqueous nanodroplets (AnDs) on a microelectrode were observed in situ by electrochemistry. Reduction of Cu2+ ions enclosed in the reacting AnDs resulted in surfactant-free synthesis of copper nanoparticles on the electrode surface. The particle size distribution was reasonably controllable by the modulation of electrode voltage. The versatility of the synthetic method was established by its application in synthesizing nanoparticles of silver and cobalt oxyhydroxide.