Catalytic Active Sites Determination and Charge Transport of Transition Metal Oxides for Oxygen Evolution Reaction

Abstract

The oxygen evolution reaction (OER) is a key process that enables the storage of renewable energies in the form of chemical fuels.[1] Unraveling the catalytic mechanism is of paramount significance for the rational design of efficient electrocatalysts.[1] Here, we use well-defined crystalline cobalt oxyhydroxides CoOOH nanorods and nanosheets as model catalysts to investigate the geometric catalytic active sites.[2] We disclose a linear correlation of catalytic activities with their lateral surface areas, suggesting that the active sites are exclusively located at lateral facets rather than basal facets. Theoretical calculations show that the coordinatively unsaturated cobalt sites of lateral facets upshift the O 2p-band center closer to the Fermi level, thereby enhancing the covalency of Co-O bonds to yield the reactivity. Following this, we develop a eutectic dealloying strategy to activate the porous spinel NiFe2O4 nanowires with up to four metal cation substitutions.[3] Spinel oxide of NiFeXO4 (X= Fe, Ni, Al, Mo, Co, Cr, ~195 mV@10mA·cm-2) outperforms most spinel phase OER electrocatalysts and comparable to the state-of-the-art NiFe hydroxides. This work elucidates the geometrical catalytic active sites and enlightens the surface engineering for efficient OER catalysts. Besides, we studied the dependence of catalytic performances on electrical conductivities and unveils that charge transportability, to our surprise, regulates the reaction kinetics of the electronically accessible active sites.[4] Remarkably, the regulation extent correlates with the electrical conductivities, suggesting the strong coupling of the electrocatalytic process with electronic transport. Furthermore, we argue the origin of Ov-promoted catalytic activities of NiFe-based (oxy)hydroxides.[5] We uncover the pivotal role of charge transport for their electrocatalytic OER and propose that the superficial Ov imposes electron donation to the conductive band of NiFeOOH and therefore enables the regulation of electronic transport to switch on/off OER catalysis. The work highlights the pivotal role of electronic transportability in unfolding catalytic potential, holding both fundamental and technical implications for electrocatalysts. Fang Song, ..., and Xile Hu*. Am. Chem. Soc. 2018, 140, 7748; Fang Song, Xile Hu*. Nat. Commun. 2014, 5, 4477; Fang Song, Xile Hu*, J. Am. Chem. Soc. 2014, 136, 16481-16484; Fang Song, ..., Hao Ming Chen,* Clemence Corminboeuf,* Xile Hu *. ACS Cent. Sci. 2019, 5, 558; Chen, Wenshu; Gu, Jiajun*; Du, Yongping*; Song, Fang*; ...; Zhang, Di. Adv. Funct. Mater. 2019, 30, 2000551; Bowen Liu, ..., Fang Song,* Qinglei Liu.* ACS Nano 2022, 16, 9, 14121.Sihong Wang, Qu Jiang, ..., and Fang Song,* Commun. 2022, 13, 6650;Qiwen Zhang, ..., Fang Song*, Mingwei Chen, and Pan Liu*. ACS Nano 2023, 17, 1485.Haoyue Zhang,# Lingling Wu,# ..., and Fang Song*., ACS Appl. Mater. Interfaces, In revision.Haoyue Zhang,# Lingling Wu,# ..., and Fang Song*. ACS Catal. In press.