Operando Unraveling Photothermal-Promoted Dynamic Active Sites Generation in Spinel NiFe2O4 for Oxygen Evolution

Abstract

The ability to develop highly active and low-cost electrocatalysts represents an important endeavor toward accelerating sluggish water-oxidation kinetics. Herein, we report, for the first time, the implementation and unravelling of photothermal effect of spinel nanoparticles (NPs) on promoting dynamic active sites generation to markedly enhance their oxygen evolution reaction (OER) activity via an integrated operando Raman and density functional theory (DFT) study. Specifically, NiFe2O4 (NFO) NPs are first synthesized by capitalizing on amphiphilic star-like diblock copolymers as nanoreactors. Upon the NIR light irradiation, the photothermal heating of the NFO-based electrode progressively raises the temperature, accompanied by a marked decrease of overpotential. Accordingly, only an overpotential of 309 mV is required to yield a high current density of 100 mA cm-2, greatly lower than recently-reported earth-abundant electrocatalysts. More importantly, photothermal effect of NFO NPs not only significantly reduces the activation energy necessitated for water splitting, but also facilitates surface reconstruction into high-active oxyhydroxides at lower potential (1.36 V) under OER conditions, as revealed by operando Raman spectra-electrochemistry. Moreover, the DFT calculation corroborates that these reconstructed (Ni,Fe)oxyhydroxides are electrocatalytically active sites as the kinetics barrier is largely reduced over pure NFO without surface reconstruction. Given the diversity of materials (metal oxides, sulfides, phosphides, etc.) possessing the photo-to-thermal conversion, this effect may thus provide a unique and robust platform to boost highly-active surface species in nanomaterials for fundamental understanding of enhanced performance that may underpin future advances in electrocatalysis, photocatalysis, solar energy conversion and renewable energy production.

Tailoring oxygen evolution reaction activity of metal-oxide spinel nanoparticles via judiciously regulating surface-capping polymers

“…† Subsequently, the as-prepared star-like diblock copolymers were utilized as nanoreactors for the synthesis of polymerligated CFO NPs (Scheme 1b and c, steps 5-6). 49 Typically, the synthesis procedure for the formation of CFO NPs remains consistent regardless of the star-like diblock copolymer nanoreactors used. Specically, the nanoreactors were rst dissolved in the mixture of diphenyl ether (DPE) and benzyl alcohol (BA) (DPE : BA ¼ 9 : 1 by volume) to form unimolecular, stable spherical micelles 50 (see Experimental section).…”

“…Since the PAA chains are partially collapsed in this solvent, BA, which is a good solvent for PAA and a poor solvent for PS, is added to promote a less-collapsed star-like PAA core with partially collapsed PS outer blocks. 49 Subsequently, specic amounts of the CFO precursors were added into the solvent mixture under vigorous stirring (see Experimental section). The metal precursors were selectively loaded into the compartment occupied by the PAA core due to the strong coordination between the carboxyl groups of PAA blocks and metal moieties of the precursors.…”