Synergic effects enhance the catalytic properties of alpha-Ni(OH)2-FeOCPc@rGO composite for oxygen evolution reaction

Nanocatalysis MoS2/rGO: An Efficient Electrocatalyst for the Hydrogen Evolution Reaction

In this study, a systematic investigation of MoS2 nanostructure growth on a SiO2 substrate was conducted using a two-stage process. Initially, a thin layer of Mo was grown through sputtering, followed by a sulfurization process employing the CVD technique. This two-stage process enables the control of diverse nanostructure formations of both MoS2 and MoO3 on SiO2 substrates, as well as the formation of bulk-like grain structures. Subsequently, the addition of reduced graphene oxide (rGO) was examined, resulting in MoS2/rGO(n), where graphene is uniformly deposited on the surface, exposing a higher number of active sites at the edges and consequently enhancing electroactivity in the HER. The influence of the synthesis time on the treated MoS2 and also MoS2/rGO(n) samples is evident in their excellent electrocatalytic performance with a low overpotential.

One-Step Electrochemical Synthesis and Surface Reconstruction of NiCoP as an Electrocatalyst for Bifunctional Water Splitting

We adopted a simple one-step electrochemical deposition to acquire an efficient nickel cobalt phosphorus (NiCoP) catalyst, which avoided the high temperature phosphatization engineering involved in the traditional synthesis method. The effects of electrolyte composition and deposition time on electrocatalytic performance were studied systematically. The as-prepared NiCoP achieved the lowest overpotential (η₁₀ = 111 mV in the acidic condition and η₁₀ = 120 mV in the alkaline condition) for the hydrogen evolution reaction (HER). Under 1 M KOH conditions, optimal oxygen evolution reaction (OER) activity (η₁₀ = 276 mV) was also observed. Furthermore, the bifunctional NiCoP catalyst enabled a high-efficiency overall water-splitting by applying an external potential of 1.69 V. The surface valence and structural evolution of NiCoP samples with slowly decaying stability under alkaline conditions are revealed by XPS. The NiCoP is reconstructed into the Ni(Co)(OH)₂ (for HER) and Ni(Co)OOH (for OER) on the surface with P element loss, acting as real "active sites".

Advances in hydrogen production from electrocatalytic seawater splitting

As one of the most abundant resources on the Earth, seawater is not only a promising electrolyte for industrial hydrogen production through electrolysis, but also of great significance for the refining of edible salt. Despite the great potential for large-scale hydrogen production, the implementation of water electrolysis requires efficient and stable electrocatalysts that can maintain high activity for water splitting without chloride corrosion. Recent years have witnessed great achievements in the development of highly efficient electrocatalysts toward seawater splitting. Starting from the historical background to the most recent achievements, this review will provide insights into the current state, challenges, and future perspectives of hydrogen production through seawater electrolysis. In particular, the mechanisms of overall water splitting, key features of seawater electrolysis, noble-metal-free electrocatalysts for seawater electrolysis and the underlying mechanisms are also highlighted to provide guidance for fabricating more efficient electrocatalysts toward seawater splitting.

Sulfate-Functionalized Nickel Hydroxide Nanobelts for Sustained Oxygen Evolution

Nickel hydroxide (Ni(OH)₂)-based electrocatalysts are promising for the oxygen evolution reaction (OER) due to their low cost, but their activity and durability still need substantial improvement to meet practical application. Here, we report a sulfate-functionalized Ni(OH)₂ nanobelt (S-Ni(OH)₂) electrocatalyst, which exhibited self-enhanced OER activity due to its self-renewed surface during anodic oxidation. The S-Ni(OH)₂ was in situ grown on the nickel foam (NF) surface in potassium peroxydisulfate solution through one-step hydrothermal treatment. This material outperformed all the existing electrocatalysts in the intensity and duration of the OER activity enhancement. An overpotential drop of 70 mV is shown by the S-Ni(OH)₂/NF electrode during 110 h reaction at a current density of 100 mA cm^-2, and the overpotential remains as low as 358 mV at a current density of 200 mA cm^-2. Such activity enhancement during OER is mainly ascribed to the formation of a highly active NiOOH/Ni(SO₄)_0.3(OH)_1.4 composite on the S-Ni(OH)₂ surface as a result of gradual sulfate release. Given the facile and environmentally benign fabrication process (without external addition of a Ni source and surfactant) and good electrochemical properties (high activity and long lifetime), the S-Ni(OH)₂ holds great potential for practical OER application. The surface self-renewal strategy developed here might also be expanded to other electrocatalysts and electrochemical processes.

Effects of a strong π-accepting ancillary ligand on the water oxidation activity of weakly coupled binuclear ruthenium catalysts

Significant differences were found in the proton-coupled redox chemistry and catalytic behavior of the binuclear [{Ru(H2O)(bpz)}2(tpy2ph)](PF6)4 complex [bpz = 2,2'-bipyrazine; tpy2ph = 1,3-bis(4'-2,2':6',2''-terpyridin-4-yl)benzene] as compared with the structurally analogous derivative with 2,2'-bipyridine (bpy) instead of bpz. The differences were assigned to the stronger π-accepting character of bpz relative to bpy as the ancillary ligand. The expectation of a positive shift for the Ru-centered redox potentials was confirmed for the lower oxidation state species, but that trend was reversed in the formation of the high-valence catalytic active species as shown by a negative shift of 0.14 V for the potential of the [RuIV/V[double bond, length as m-dash]O] process. Moreover, DFT calculations indicated a significant decrease of about 15% on the spin density and oxyl character of the [RuV[double bond, length as m-dash]O]3+ fragment. The significantly lower kcat(O2) for the bpz system was attributed to these combined electronic effects.