Laser Fragmentation‐Induced Defect‐Rich Cobalt Oxide Nanoparticles for Electrochemical Oxygen Evolution Reaction

Abstract

Sub‐5 nm cobalt oxide nanoparticles are produced in a flowing water system by pulsed laser fragmentation in liquid (PLFL). Particle fragmentation from 8 nm to 4 nm occurs and is attributed to the oxidation process in water where oxidative species are present and the local temperature is rapidly elevated under laser irradiation. Significantly higher surface area, crystal phase transformation, and formation of structural defects (Co2+ defects and oxygen vacancies) through the PLFL process are evidenced by detailed structural characterizations by nitrogen physisorption, electron microscopy, synchrotron X‐ray diffraction, and X‐ray photoelectron spectroscopy. When employed as electrocatalysts for the oxygen evolution reaction under alkaline conditions, the fragmented cobalt oxides exhibit superior catalytic activity over pristine and nanocast cobalt oxides, delivering a current density of 10 mA cm−2 at 369 mV and a Tafel slope of 46 mV dec−1, which is attributed to a larger exposed active surface area, the formation of defects, and an increased charge transfer rate. The study provides an effective approach to engineering cobalt oxide nanostructures in a flowing water system, which shows great potential for sustainable production of active cobalt catalysts.

Inspirations of Cobalt Oxide Nanoparticle Based Anticancer Therapeutics

“…They used coffee grounds as a sustainable hard template to prepare spinel cobalt oxide through a simple method. Then, a mild reduction process was used to obtain cobalt oxide while maintaining a mesoporous structure composed of about 8 nm particles [33]. It was an effective method to construct cobalt oxide nanoparticles in a flowing water system, which was conducive to the sustainable production of active cobalt catalysts.…”

Laser Irradiation of Electrode Materials for Energy Storage and Conversion

“…24 Despite these remarkable advantages, LFL technology offers a very low efficiency. As a result, innovative strategies capable of mass production, for example lasing the target in flowing liquids, 77 are actively pursued to surmount this deficiency.…”

Laser Synthesis of Colloids: Applications

“…Here, adsorption of the laser-generated nanoparticles is forced by the electrostatic interaction of the nanoparticles and the support material due to proper pH adjustment (Wagener et al 2012a;Marzun et al 2014). This consecutive synthesis protocol not only allows tuning of the laser-generated nanoparticles but also of the defect structure and properties of the support before subsequent adsorption of the former on the latter (Waag et al 2017;Lau et al 2018;Siebeneicher et al 2020;Yu et al 2020). Consequently, laser-generated NPs are becoming increasingly important for the use in heterogeneous catalysis which is evident in the literature.…”

“…Since activation steps like calcination knowingly change the catalysts before testing or even forming the catalyst itself in the first place (e.g., in case of an aging step during coprecipitation), calcination temperature and atmosphere hence need careful tuning (Hutchings 2008;Kuhn et al 2009). The independence of laser-generated catalysts from these pre-treatments allows to investigate structure-activity correlations without cross-correlations from changes of crystallinity, particle size, and metal composition during calcination (Reichenberger et al 2019;Lau et al 2018;Yu et al 2020).…”