Ultrasmall iridium oxide nanoparticle incorporated nitrogen-doped carbon derived from the electropolymerized 1,10-phenanthroline-based molecules for water oxidation reactions

Abstract

Water electrolysis is a promising route in the mass production of hydrogen using electricity generated from renewable energy sources. Water oxidation reaction (WOR), the anodic reaction of water electrolyzers, requires large overpotential and limits the overall efficiency, and active and stable WOR electrocatalysts are needed. We prepare ultrasmall iridium oxide nanoparticles (IrO x , ~ 1.23 nm in diameter) incorporated in nitrogen-doped carbon via electropolymerization of 1,10-phenanthroline-based molecules in the presence of IrO x followed by calcination under nitrogen. The resulting electrodes are active and stable to electrochemically catalyze WOR in acid. The most active electrode, IrO x @P(2Nphen), requires only 270 mV overpotentials to reach 10 mA cm −2 WOR current densities and exhibits the mass-normalized specific activity of 1.75 A m g Ir − 1 at 310 mV overpotentials. The abundant N atoms in the nitrogen-doped carbon provide hydrogen bonding to facilitate the charge transfer process, and the electron interaction between the N atoms and IrO x alters the adsorption energy of water oxidation intermediate (OH*). Both factors contribute to the observed high WOR performance. A water electrolyzer is assembled using the IrO x @P(2Nphen) as the anode and carbon paper supported commercial Pt/C catalysts as the cathode. Only 1.54 V cell voltage is required to reach the 10 mA cm −2 current densities for overall water splitting. This study provides a facile method to prepare ultrasmall IrO x incorporated nitrogen-doped carbon for WOR, and this synthetic method can potentially be applied to prepare other nanoparticle incorporated carbon-based materials. • Ultrasmall IrO x nanoparticles are incorporated in nitrogen-doped carbon by electropolymerization and calcination. • The N content of the nitrogen-doped carbon is tunableby selecting monomers withdifferent numbers of amine group. • The most active electrode requires 270 mV overpotential to reach 10 mA cm −2 WOR current density in acid. • The electron interaction facilitates the WOR intermediate adsorption..