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

• Published in: ChemSusChem Vol. 13; no. 3; pp. 520 - 528
• Main Authors: Yu, Mingquan, Waag, Friedrich, Chan, Candace K., Weidenthaler, Claudia, Barcikowski, Stephan, Tüysüz, Harun
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 07.02.2020; John Wiley and Sons Inc
• Subjects: Catalytic activity; Charge transfer; Cobalt; Cobalt oxides; Crystal defects; Crystal structure; Defects; electrocatalysis; Electrocatalysts; Fragmentation; Lasers; metal oxides; Nanoparticles; nanostructures; Oxidation; oxygen evolution reaction; Oxygen evolution reactions; Phase transitions; Photoelectrons; Pulsed lasers; structural defects; Surface area; structural defects; oxygen evolution reaction; metal oxides; electrocatalysis; nanostructures
• ISSN: 1864-5631; 1864-564X; 1864-564X
• DOI: 10.1002/cssc.201903186

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. Smash it up: Sub‐5 nm cobalt oxide nanoparticles are produced by pulsed laser fragmentation in liquid (PLFL) in a flowing water system. Significantly larger surface area, crystal oxidation, and the formation of structural defects (Co2+ defects and oxygen vacancies) are evidenced through the PLFL process, leading to a superior catalytic activity for the oxygen evolution reaction.