Ultrasmall Co@Co(OH)₂ Nanoclusters Embedded in N‐Enriched Mesoporous Carbon Networks as Efficient Electrocatalysts for Water Oxidation

Abstract

Metal nanoclusters (NCs, size ≤2 nm) are emerging materials in catalysis owing to their unique catalytic and electronic properties such as high surface/volume ratio, high redox potential, plethora of surface active sites, and dynamic behavior on a suitable support during catalysis. Herein, in situ growth of ultrasmall and robust Co@β‐Co(OH)2 NCs (≈2 nm) hosted in a honeycomb‐like 3D N‐enriched carbon network was developed for water‐oxidation catalysis with extremely small onset potential (1.44 V). Overpotentials of 220 and 270 mV were required to achieve a current density of 10 mA cm−2 and 100 mA cm−2, respectively, in alkaline medium (1 m KOH). More promisingly, at η10=240 mV, the prolonged oxygen evolution process (>130 h) with faradaic efficiency >95 % at a reaction rate of 22 s−1 at 1.46 V further substantiated the key role of the ultrasmall supported NCs, which outperformed the benchmark electrocatalysts (RuO2/IrO2) and NCs reported so far. It is anticipated that the high redox potential of NCs with regeneratable active sites and their concerted synergistic effects with the N‐enriched porous/flexible carbon network are inherently worth considering to enhance the mass/charge transport owing to the nanoscale interfacial collaboration across the electrode/electrolyte boundary, thereby efficiently energizing the sluggish/challenging oxygen evolution process.

Bioactivities of Geranium wallichianum Leaf Extracts Conjugated with Zinc Oxide Nanoparticles

“…The term "nano" is a Greek word which means "extremely small or dwarf" in size range of about one to one-hundred nanometers. NPs possess unique and fascinating magnetic, electrical, optical, and chemical properties with small size, different shapes, and surface effects compared to bulk materials [1][2][3]. NPs possess breakthrough applications in different fields such as food, agriculture, medicine, cosmetics, energy, environment, and many more [4,5].…”

Controlled Assembly of Cu/Co‐Oxide Beaded Nanoclusters on Thiolated Graphene Oxide Nanosheets for High‐Performance Oxygen Evolution Catalysts

“…In the Co/CoO@G-SH nanohybrid, the core-levels pectrum of Co shows peaks at 777.17 eV and 795.7 eV corresponding to 2p 3/2 and 2p 1/2 of Co 0 , whereas peaks at binding energies of 781.4 eV and 798.2 eV can be attributedt oC o 2 + 2p 3/2 and 2p 1/2 ,r espectively,w ith a characteristic splitting factor of approximately 16 eV arising from the spin-orbit coupling.I na ddition, the shake-up satellite peak at 786.7 eV (shoulder peak merged with 2p 3/2 )f urther confirmst he presence of Co 2 + as reportedp reviously (Figure 3g). [24] Similarly,t he core spectrum of Cu 2p of Cu/CuO@G-SH shows peaks at binding energies of 934.5 eV and 954.6 eV correspondingt oC u 2 + 2p 3/2 and Cu 2 + 2p 1/2 ,r espectively (Figure 3f). The energy difference between the 2p 3/2 and2 p 1/2 levels is about 20 eV,a rising from the spin-orbit coupling of the CuO x nanostructure.…”

“…In this regard, we appliedt he water displacement method according to our previous report (see the Experimental Section). [24] The FE of BNCs@G-SH ( % 96 %) and NCs@G-SH ( % 93.5 %) implies the selectivity of the electrode materialf or OER, and meanwhile rules out the possibility of any side reaction ( Figure S8 in the Supporting Information). To better understand the true electronic nature of such ultrasmall nanostructures after catalysis, we analyzed the electrolyte before and after OER by using ICP-OESt oq uantify the Cu or Co, if any.T he absence of Cu or Co in the electrolyte validates the strong electronic contact of the catalyst-support, therebye liminating the dissolution of catalysts in the electrolyte, which is generally expected in the case of higher oxidation states of metals (Table S2 in the Supporting Information).…”

“…[23] More recently,w ee xplored Co(OH) 2 NCs hostedo nN -doped mesoporous carbon and NiO x NCs on sulfur-functionalized graphene oxide (GO) for the OER, and found that NCs are indeed highly regarded for OER, where the number/exposure of active sites and stability can be significantly improved by assembling them on a suitable conductive support. [13,[24][25][26] Similarly,l ayer double hydroxides (LDH) of Ni-Mn were recently reported for efficient OER with the potential to offer numerous active anda ccessible sites by controlling the thickness (1.3 nm) of the nanosheets. [27] Among the various conducting supports, GO has emerged as the subjecto fi ntenser esearch as an essential component of electrode materials owing to its excellent mechanical strength and unparalleledt hermal and superior electronic properties.…”

Electrochemical Characterisation of Co@Co(OH)2 Core‐Shell Nanoparticles and their Aggregation in Solution

“…Whilst the shell maintains the magnetic functionality of the cobalt core, the control of its chemical composition may lead to additional beneficial properties of the nanoparticles and future possible applications in nanomedicine [15] . For instance, the layered crystal structure of the Co(OH) 2 shell of Co@Co(OH) 2 NPs has been shown to have a large specific capacitance, [16] and the hydroxide is also electrocatalytically active towards the oxygen evolution reaction, [17] the hydrogen evolution reaction [18] and the hydrogenation of nitrile/nitro compounds [18–19] …”