The reductive supercritical hydrothermal process, a novel synthesis method for cobalt nanoparticles: synthesis and investigation on the reaction mechanism

Abstract

Highly crystalline cobalt nanoparticles with low surface oxidation were synthesized by the reductive supercritical hydrothermal process in the temperature range from 340 to 420 °C. Under these reaction conditions, hydrogen generated from formic acid decomposition is maximally soluble in water, enabling the effective reduction of cobalt ions and cobalt oxide. The reaction mechanism was investigated by kinetic analysis on the formation of cobalt nanoparticles. This analysis assumed the first order irreversible reaction and two different types of shrinking core models (chemical reaction and inter-diffusion dominated). According to the proposed reaction mechanism, cobalt monoxide is probably formed at the early reaction stage, where insufficient H2 is available, or under high temperature conditions. Moreover, cobalt monoxide influences the entire reaction rate. Thus, suppressing the formation and growth of cobalt monoxide is of primary importance in the optimal synthesis of cobalt nanoparticles by the reductive supercritical hydrothermal process.

Co@Co3O4@PPD Core@bishell Nanoparticle‐Based Composite as an Efficient Electrocatalyst for Oxygen Reduction Reaction

“…[ 13 ] The pyrolysis of Co@PDA in N 2 at 900 ºC renders a composite of Co NPs encapsulated in pyrolyzed polydopamine (PPD), i.e., Co@PPD, with the crosslinked units of indolequinone being converted to graphitic C-N structure concurrently (Scheme 1 a). Upon mild heating to 90 °C in air, the reactive Co NPs inside core-shell Co@PPD [ 3a ] capture oxygen in air to form core@bishell Co@Co 3 O 4 Figure 1 .…”

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Understanding bottom-up continuous hydrothermal synthesis of nanoparticles using empirical measurement and computational simulation

“…Figure 1 shows a range of particles from metals to oxides to sulfides that were synthesized during the SHYMAN project, which funded this research work. Non-oxide synthesis has involved the use of a solvothermal method [23], combined hydrothermalsolvothermal method [24], the addition of reductants [25,26], or a selection of reagents to control the oxidation states [27]. Santamaria's review also highlighted the critical need to control the particle size and particle size distribution, and it is this area of quality control that is most affected during the scale up of a manufacturing process from bench to pilot to full scale.…”