In situ evolution of highly dispersed amorphous CoOx clusters for oxygen evolution reaction

Plasma-catalysed reaction Mn+ + L–H → MOFs: facile and tunable construction of metal–organic frameworks in dielectric barrier discharge

A fast, energy-saving and green strategy was proposed for preparing diverse and fine-tuned metal–organic frameworks in either DMF or ethanol, catalyzed by liquid-phase plasma generated via dielectric barrier discharge.

Serpentine Ni3 Ge2 O5 (OH)4 Nanosheets with Tailored Layers and Size for Efficient Oxygen Evolution Reactions

Layered serpentine Ni₃ Ge₂ O₅ (OH)₄ is compositionally active and structurally favorable for adsorption and diffusion of reactants in oxygen evolution reactions (OER). However, one of the major problems for these materials is limited active sites and low efficiency for OER. In this regard, a new catalyst consisting of layered serpentine Ni₃ Ge₂ O₅ (OH)₄ nanosheets is introduced via a controlled one-step synthetic process where the morphology, size, and layers are well tailored. The theoretical calculations indicate that decreased layers and increased exposure of (100) facets in serpentine Ni₃ Ge₂ O₅ (OH)₄ lead to much lower Gibbs free energy in adsorption of reactive intermediates. Experimentally, it is found that the reduction in number of layers with minimized particle size exhibits plenty of highly surface-active sites of (100) facets and demonstrates a much enhanced performance in OER than the corresponding multilayered nanosheets. Such a strategy of tailoring active sites of serpentine Ni₃ Ge₂ O₅ (OH)₄ nanosheets offers an effective method to design highly efficient electrocatalysts.

Doping β-CoMoO4 Nanoplates with Phosphorus for Efficient Hydrogen Evolution Reaction in Alkaline Media

Mass production of hydrogen by electrolysis of water largely hinges on the development of highly efficient and economical electrocatalysts for hydrogen evolution reaction (HER). Though having the merits of high earth abundance, easy availability, and tunable composition, transition-metal oxides are usually deemed as poor electrocatalysts for HER. Herein, we demonstrate that doping β-CoMoO₄ nanoplates with phosphorus can turn them into active electrocatalysts for HER. Theoretical calculation and experimental studies unravel that enhanced electrical conductivity and optimized hydrogen adsorption free energy are major causes for the improvement of intrinsic activity. As a result, only an overpotential of 138 mV is required to drive hydrogen evolving at a current density of 10 mA cm^-2 in 1 M KOH for P-doped β-CoMoO₄, which outstrips many recently reported transition-metal oxides and is just slightly inferior to commercial Pt/C. This work opens a new route to tune the HER performance of transition-metal oxides.

Self-supported nickel-cobalt nanowires as highly efficient and stable electrocatalysts for overall water splitting

The development and design of highly active and stable electrocatalysts based on cheap and Earth-abundant materials is critically important to enable water splitting as a desirable renewable energy source. Herein, we fulfill the significant electrochemical water splitting enhancement in both electrocatalytic activity and durability by constructing self-supported nickel-cobalt nanowire catalysts with abundant oxygen vacancies. Specifically, the rich oxygen vacancies can largely promote the oxygen evolution reaction (OER) activity of optimal Ni₁Co₁O₂ NWs with a relatively low overpotential of 248 mV to drive a current density of 10 mA cm^-2. More significantly, after the phosphorization of Ni₁Co₁O₂ NWs, the resultant Ni₁Co₁P NWs can also display excellent electrocatalytic hydrogen evolution reaction (HER) performances with an overpotential of only 101 mV to achieve a current density of 10 mA cm^-2. Furthermore, benefiting from the unique 1D nanowire structure, the synergistic effect, and the optimal Gibbs free energy for hydrogen evolution evolved from the phosphorization, the Ni₁Co₁O₂ NWs//Ni₁Co₁P NWs couple is thus highly active and stable for overall water electrolysis with a low voltage of 1.58 V at 10 mA cm^-2, showing extraordinary promise for practical overall water splitting electrolysis.

Disordering the Atomic Structure of Co(II) Oxide via B-Doping: An Efficient Oxygen Vacancy Introduction Approach for High Oxygen Evolution Reaction Electrocatalysts

The introduction of oxygen (O) vacancies has been considered to be an important but challenging way to enhance the activity of electrocatalysts for the oxygen evolution reaction (OER). Substitution by heteroatoms with high electron-donating ability may be a feasible strategy for triggering O-vacancies to maintain thermodynamic stability. Herein, density functional theory (DFT) calculations predict that the incorporation of boron (B) is favorable to the generation of O-vacancies in transition metal oxides. Then, CoO nanowires with O-vacancies are prepared via incorporation of B using a facile pyrolysis strategy. As evidenced by the combined results of electron paramagnetic resonance spectroscopy and X-ray absorption near edge structure, O-vacancies in CoO are mainly derived from the disordering of the local structure caused by B doping. DFT calculation results further reveal that the oxidation of *OOH is the rate-limiting step for O-vacancies enriched CoO in the OER and that the presence of O-vacancies can efficiently lower the reaction barrier for breaking CoO bond, contributing to the improvement of OER kinetics. As expected, the O-vacancies enriched CoO exhibits a low overpotential of 280 mV to reach the current density of 10 mA cm^-2 under basic conditions.

Rapid cationic defect and anion dual-regulated layered double hydroxides for efficient water oxidation

Defect engineering and anionic regulation are effective approaches to improve the intrinsic activity of oxygen evolution reaction (OER) catalysts, particularly for highly efficient and low-cost cobalt-based electrocatalysts. Layered double hydroxides (LDHs) are considered as promising electrocatalysts toward OER. However, their electronic properties and active sites need to be optimized for their large-scale application. Herein, rapidly cationic defect and anion dual-regulated CoAl LDHs (PS-CoAl LDHs) were in situ synthesized in a few minutes via a modified water DBD plasma treatment. Abundant Al3+ vacancies and a relatively rough surface for S2- regulation were formed by the etching effect of the plasma. Consequently, the as-obtained PS-LDHs possess improved intrinsic conductivity and an optimal electronic structure. Simultaneously, the synergistic effect of the Al3+ vacancies and S2- regulation promote the exposure of active Co sites, resulting in an amorphous and porous surface for improving the OER performance.

Preferential Cation Vacancies in Perovskite Hydroxide for the Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is an ideal model to study the relationship between the activity and the surface properties of catalysts. Defect engineering has been extensively developed to tune the electrocatalytic activity for OER. Compared to the anion vacancies in metal oxides, cation vacancies are more challenging to selectively generate, and the insight into the structure and activity of cation vacancies-rich catalysts are lacked. Herein, using SnCoFe perovskite hydroxide as a precursor, abundant Sn vacancies on the surface were preferentially produced by Ar plasma. Sn vacancies could be preferentially produced as confirmed by the X-ray absorption spectra, probably owing to the lower lattice energy and weaker chemical bonds of Sn(OH)₄ . The Sn vacancies promoted the exposure of active CoFe sites, resulting in an amorphous surface layer, modulated the conductivity, and thus enhanced the OER performance.

Porous Cobalt Oxynitride Nanosheets for Efficient Electrocatalytic Water Oxidation

Exploring efficient and cheap oxygen evolution reaction (OER) electrocatalysts is of great significance for electrochemical water splitting. Herein, we successfully prepared an efficient ternary electrocatalyst of porous cobalt oxynitride (Co₃ O_x N_y ) nanosheets by a simple nitridation strategy. Specifically, CoON PNS-400 (cobalt oxynitride with porous nanosheet structure obtained at 400 ^o C) offered a low OER overpotential of 0.23 V to achieve the catalytic current density of 10 mA cm^-2 and a small Tafel slope of 48 mV dec^-1 in alkali media, outperforming most of the first-row transition-metal-based OER electrocatalysts. The calculated density of states (DOS) analysis and electron spin resonance (ESR) measurements revealed that the introduction of foreign N atoms into pristine Co₃ O₄ nanosheets can optimize the electronic structure and create more oxygen vacancies, thus leading to enhanced electrical conductivity. Density functional theory (DFT) calculations demonstrated that the foreign N atoms can also improve the energetics for OER by modulating the free energy for adsorbed intermediates (OOH*, OH*, O*), further improving the OER electrocatalytic activity of CoON PNS-400. This work provides a possibility for rationally designing ternary transition-metal compounds as advanced OER electrocatalysts.

Self-Template Synthesis of Co-Se-S-O Hierarchical Nanotubes as Efficient Electrocatalysts for Oxygen Evolution under Alkaline and Neutral Conditions

We develop a facile self-template synthetic method to construct hierarchical Co-Se-S-O (CoSe _xS_{2- x}@Co(OH)₂) nanotubes on a carbon cloth as a self-standing electrode for electrocatalytic oxygen evolution reaction (OER). In the synthetic process, separate selenization and sulfurization on the Co(OH)F precursor in different solvents have played an important role in constructing CoSe _xS_{2- x} (Co-Se-S) hierarchical nanotubes, which was further transformed into the nanotube-like Co-Se-S-O via an in situ electrochemical oxidation process. The Co-Se-S-O obtained by the Kirkendall effect through two stepwise anion-exchange reactions represents the first quaternary Co-Se-S-O nanotube array, which dramatically enhances its surface area and conductivity. Further, it only requires low overpotentials of 230 and 480 mV to achieve a 10 mA cm^-2 current density. The OER performance of Co-Se-S-O is much more efficient than that of its monochalcogenide counterparts, as well as the commercial benchmark catalyst IrO₂.

Electrocatalytic oxygen evolution with a cobalt complex

The development of an earth-abundant, first-row water oxidation catalyst that operates at a high TOF and a low overpotential remains a fundamental chemical challenge. Cobalt complexes are important members of water oxidation catalysts. Herein, we report a cobalt-based robust homogeneous water oxidation catalyst, which can electrocatalyze water oxidation at a high pH and a low overpotential (η = 520 mV) in phosphate buffer. This homogeneous system exhibits a high turnover frequency (about 5 s^-1) of catalyzing water oxidation to produce oxygen at η = 720 mV. We speculate the mechanism of the reaction that O-O bond formation prefers a HO-OH coupling in catalytic water oxidation.

Ultrasonication-assisted synthesis of ternary-component Ni3AlxFe1−x-layered double hydroxide nanoparticles for the oxygen evolution reaction in a neutral solution

In this study, ultrasonication, a facile and rapid process, was utilized for the preparation of ternary-component layered double hydroxides (LDHs), Ni₃Al_xFe_1−x-LDHs, as the electrocatalyst material for the oxygen evolution reaction (OER) in a neutral solution.

Rapid synthesis of Co3O4 nanosheet arrays on Ni foam by in situ electrochemical oxidization of air-plasma engraved Co(OH)2 for efficient oxygen evolution

Rapid synthesis of Co₃O₄@NF as an efficient electrocatalyst for the OER by direct in situ electrochemical oxidization of air-plasma engraved Co(OH)₂@NF.

Gold doping induced strong enhancement of carbon quantum dots fluorescence and oxygen evolution reaction catalytic activity of amorphous cobalt hydroxide

Au doping leads to tunable and strong enhancement of SCQDs fluorescence and OER activity of amorphous Co(OH)₂.

In situ growth of cobalt@cobalt-borate core-shell nanosheets as highly-efficient electrocatalysts for oxygen evolution reaction in alkaline/neutral medium

Development of efficient non-noble metal electrocatalysts for oxygen evolution reaction (OER) is still a crucial issue for renewable energy technologies. Herein, we report a core-shell-like catalyst of amorphous cobalt borate nanosheets grown on metallic cobalt deposited on Ti-mesh (Co@Co-Bi/Ti) by an in situ conversion strategy. Benefiting from the high activity, large surface area of Co-Bi nanosheets, outstanding electronic conductivity of metallic Co and the 3D structure inherited from Ti-mesh substrate, Co@Co-Bi/Ti shows high OER activity with a relatively small overpotential of 329 mV to obtain a current density of 10 mA cm^-2, a low Tafel slope of 46 mV dec^-1 and an accessible large current density of 500 mA cm^-2 in alkaline solution. Besides, Co@Co-Bi/Ti exhibits good performance in a near-neutral medium. This study provides an effective pathway to improve the cobalt metal based materials.

Ru decorated with NiCoP: an efficient and durable hydrogen evolution reaction electrocatalyst in both acidic and alkaline conditions

NiCoP@Ru is an excellent hydrogen evolving catalyst in both acidic and alkaline conditions, close in performance to that of Pt/C.