Bimetal Networked Nanosheets Co x Ni 3−x S 2 as An Efficient Electrocatalyst for Hydrogen Evolution

Manipulating the Dynamic Self-Reconstruction of CoP Electrocatalyst Driven by Charge Transport and Ion Leaching

Surface reconstruction of electrocatalysts is very important to clarify the structure-component-activity relationship. In this work, in situ Raman and ex situ technologies are used to capture the surface structure evolution of F-Fe-CoP during the oxygen evolution reaction (OER). The results reveal that the leaching of F accelerates the dynamic reconstruction response of CoP to rapidly convert into active (oxy)hydroxide species. The further introduction of Fe can accelerate the charge transfer rate and alleviate the structural stacking caused by insufficient kinetics. The introduction of F and Fe increases the electron occupation states of cobalt sites and promotes the adsorption of OH- ions on the CoP catalyst, which significantly improves the OER performance. F-Fe-CoP exhibits excellent OER performance with an overpotential of 259 mV at 20 mA cm-2 . This finding enriches the OER mechanism associated with the surface reconstruction of CoP and provides a reference for the rational design of efficient electrocatalysts.

Bimetallic Multi-Level Layered Co-NiOOH/Ni3 S2 @NF Nanosheet for Hydrogen Evolution Reaction in Alkaline Medium

Development of efficient non-noble metal catalysts for water splitting is of great significance but challenging due to the sluggish kinetics of the hydrogen evolution reaction (HER) in alkaline medium. Herein, a bimetallic multi-level layered catalytic electrode composed of Ni₃ S₂ nanosheets with secondary Co-NiOOH layer of 3D porous and free-standing cathode in alkaline medium is reported. This integrated synergistic catalytic electrode exhibits excellent HER electrocatalytic performance. The resultant Ni_0.67 Co_0.33 /Ni₃ S₂ @NF electrode displays the highest HER activity with only overpotentials of 87 and 203 mV to afford current densities of 10 and 100 mA·cm^-2 , respectively, and its Tafel slope is 80 mV·dec^-1 . The chronopotentiometry operated at high current density of 50 mA·cm^-2 shows negligible deterioration, indicating better stability of Ni_0.67 Co_0.33 /Ni₃ S₂ @NF electrode than Pt/C (20 wt.%). Such a desirable catalytic performance is attributed to the modification of physical and electronic structure that exposes abundant active sites and improves the intrinsic catalytic activity toward HER, which is also confirmed by electrochemically active surface area and X-ray photoelectron spectroscopy analysis. This work provides a strong support for the rational design of high-performance bimetallic electrodes for industrial water splitting.

Three-dimensional cross-linked Co-MoS2 catalyst on carbon cloth for efficient hydrogen evolution reaction

MoS₂-Based materials are promising hydrogen evolution reaction (HER) electrocatalysts. However, their HER activities are restrained by the poor population of HER activated edge centers, the large area exposed HER inert basal planes, and low conductivity. Fixing these problems on one system is an effective strategy, but it remains a challenge due to the harsh synthetic conditions. Herein, cobalt carbonate hydroxide (CoCH) nanosheets were used as the substrate for preparing a three-dimensional self-supported cross-linked (3DSC) Co-MoS₂ nanostructured HER catalyst, which possesses abundant active centers and fast electronic transfer ability. In addition, Co activates the basal-plane sulfur atom in MoS₂ to be the HER reactive center effectively. Benefiting from these advantages, 3DSC Co-MoS₂ electrode integrated on carbon cloth (CC) shows that it can drive the current density of 10 and 100 mA cm^-2 with only 40 and 119 mV overpotentials, respectively, which is superior to other MoS₂-based HER catalysts reported recently. This research provides a facile strategy for the improvement of efficient HER electrocatalysts.

Insights on the Electrocatalytic Seawater Splitting at Heterogeneous Nickel-Cobalt Based Electrocatalysts Engineered from Oxidative Aniline Polymerization and Calcination

Given the limited access to freshwater compared to seawater, a growing interest surrounds the direct seawater electrolysis to produce hydrogen. However, we currently lack efficient electrocatalysts to selectively perform the oxygen evolution reaction (OER) over the oxidation of the chloride ions that are the main components of seawater. In this contribution, we report an engineering strategy to synthesize heterogeneous electrocatalysts by the simultaneous formation of separate chalcogenides of nickel (NiS_x, x = 0, 2/3, 8/9, and 4/3) and cobalt (CoS_x, x = 0 and 8/9) onto a carbon-nitrogen-sulfur nanostructured network. Specifically, the oxidative aniline polymerization in the presence of metallic cations was combined with the calcination to regulate the separate formation of various self-supported phases in order to target the multifunctional applicability as both hydrogen evolution reaction (HER) and OER in a simulated alkaline seawater. The OER’s metric current densities of 10 and 100 mA cm⁻² were achieved at the bimetallic for only 1.60 and 1.63 V_RHE, respectively. This high-performance was maintained in the electrolysis with a starting voltage of 1.6 V and satisfactory stability at 100 mA over 17 h. Our findings validate a high selectivity for OER of ~100%, which outperforms the previously reported data of 87–95%.

In situ growth of an Fe-doped NiCo-MOF electrocatalyst from layered double hydroxide effectively enhances electrocatalytic oxygen evolution performance

The hierarchical book-like Fe-NiCo-MOF exhibits superior OER performance coupled with outstanding stability at a high current density.