Promising Candidates For Water Splitting Research Articles

Carbon-Encapsulated Electrocatalysts for the Hydrogen Evolution Reaction

Water electrolysis is a promising approach for large-scale and sustainable hydrogen production; however, its kinetics is slow and requires precious metal electrocatalysts to efficiently operate. Therefore, great efforts are being undertaken to design and prepare low-cost and highly efficient electrocatalysts to boost the hydrogen evolution reaction (HER). This is because traditional transition-metal electrocatalysts and corresponding hybrids with nonmetal atoms rely mainly on the interaction of metal–H bonds for the HER, which inevitably suffers from corrosion in extreme acidic and alkaline solutions. And as a result of all this effort, novel nanostructured electrocatalysts, such as carbon-encapsulated precious metals and non-precious metals including single metals or their alloys, transition-metal carbides, phosphides, oxides, sulfides, and selenides have all been recently reported to exhibit good catalytic activities and stabilities for hydrogen evolution. Here, the catalytic activity is thought to originate from the electron penetration effect of the inner metals to the surface carbon, which can alter the Gibbs free energy of hydrogen adsorption on the surface of materials. In this review, recent progresses of carbon-encapsulated materials for the HER are summarized, with a focus on the unique effects of carbon shells. In addition, perspectives on the future development of carbon-coated electrocatalysts for the HER are provided. Carbon-encapsulated electrocatalysts, such as carbon-encapsulated precious metals and non-precious metals (single metals or their alloys, metal carbides, phosphides, oxides, sulfides, and selenides), are emerging as promising candidates for water splitting. In this review, recent progresses in carbon-encapsulated electrocatalysts for hydrogen evolution are reviewed, especially the unique effects of carbon shells.

Two-Dimensional Mn-Co LDH/Graphene Composite towards High-Performance Water Splitting

The oxygen evolution reaction (OER) is a complex multi-step four-electron process showing sluggish kinetics. Layered double hydroxides (LDH) were reported as promising catalysts for the OER, but their low electrical conductivity restricts their widespread applications. To overcome this problem, a composite material containing Mn-Co LDH ultrathin nanosheet and highly conductive graphene was synthesized for the first time. Benefited from the high electrocatalytic activity and the superior charge transfer ability induced by these components, the new material shows superior OER activity. Used as the OER catalyst, a high current density of 461 mA cm−2 at 2.0 V vs. RHE (reversible hydrogen electrode) was measured besides shows a low overpotential of 0.33 V at 10 mA cm−2. Moreover, the new composite also shows a superior bifunctional water splitting performance as catalyst for the OER and HER (hydrogen evolution reaction) catalysts. Our results indicate that the presented material is a promising candidate for water splitting which is cheap and efficient.

Crystal-Face Tailored Graphitic Carbon Nitride Films for High-Performance Photoelectrochemical Cells.

Graphitic carbon nitride (g-CN) has been widely studied as a promising candidate for water splitting, owing to its metal-free nature, moderate band gap, and low cost. However, its photocurrent density is still very low for photoelectrochemical cell applications. In this work, a crystal face tailored g-CN photoelectrode has been fabricated by a facile thermal vapor deposition method. We use the melamine formaldehyde resin as a new precursor and have successfully fabricated g-CN films. The intensity ratio between two typical peaks (100) and (001) of g-CN is very different from that in the existing literature. The water splitting photocurrent density is as high as 228.2 μA cm-2 , which is 126.8 times higher than pure g-CN (1.8 μA cm-2 ) at 1.23 V vs. reversible hydrogen electrodes under one sun illumination without sacrificial reagents and co-catalysts. The electrode shows the best performance, compared with the previously reported g-CN photoelectrodes.

General Strategy for Doping Impurities (Ge, Si, Mn, Sn, Ti) in Hematite Nanocrystals

The doping of foreign atoms is critical in tailoring the properties and potential applications of semiconductor nanocrystals. A general strategy for successfully incorporating various impurities (e.g., Ge, Si, Mn, Sn, Ti) inside the regular crystal lattice of hematite (α-Fe2O3), a promising candidate for water splitting and environmental protection, is developed. Liquid-phase laser ablation-derived colloidal clusters are used as doping precursors for the metastable growth of doped hematite nanocrystals, thereby avoiding surfactants and hazardous liquid byproducts. The doping percentage, morphology, and structure of the hematite nanocrystals are greatly affected by the type and amount of the colloidal precursors used. High-resolution transmission electron microscopy and the corresponding component analysis reveal that the dopant atoms either form superlattice structures (Ge and Si) or distribute as disordered solid solutions (Mn, Sn, Ti) inside the crystal lattice of hematite. The optical absorption spectr...