Organically Capped Iridium Nanoparticles as High-Performance Bifunctional Electrocatalysts for Full Water Splitting in Both Acidic and Alkaline Media: Impacts of Metal-Ligand Interfacial Interactions

Design and engineering of bifunctional catalysts are critical in the development of electrochemical full water splitting. In this study, 4-ethylphenylacetylene-functionalized iridium (Ir-C, 1.7 ± 0.3 nm in diameter) nanoparticles are found to exhibit markedly enhanced electrocatalytic activity toward both hydrogen and oxygen evolution reactions (HER and OER) in acidic and alkaline media, in comparison to the nanoparticles capped with mercapto and nitrene derivatives. Remarkably, the HER and OER performances in alkaline media are even better than those of commercial Ir/C and Pt/C benchmarks. This is accounted for by the formation of Ir-CC-conjugated interfacial linkage that leads to significant intraparticle charge delocalization and hence manipulation of the electron density of the Ir nanoparticles and interactions with key reaction intermediates. This is indeed confirmed by results from both spectroscopic measurements and density functional theory calculations. With Ir-C nanoparticles as both the cathode and anode catalysts for electrochemical water splitting, a low cell voltage of 1.495 and 1.473 V is needed to reach the current density of 10 mA cm-2 in alkaline and acidic media, respectively. Such a performance is markedly better than that of commercial Ir/C (1.548 and 1.561 V) and relevant catalysts reported in recent literature, highlighting the significance of interfacial engineering in the development of high-performance bifunctional electrocatalysts.