Field Of Water Splitting Research Articles

N doped carbon quantum dots modified defect-rich g-C3N4 for enhanced photocatalytic combined pollutions degradation and hydrogen evolution

Exploiting metal-free cocatalysts is of huge interest for photocatalytic technology in environmental wastewater remediation and water splitting fields. The N doped carbon quantum dots (NCDs) modified defect-rich g-C3N4 (DCN) was prepared through impregnation method. The structural, optical and electronic properties of NCDs/DCN were systematically investigated. The NCDs/DCN with outstanding visible light absorption, narrowed gap and electron transfer ability were conducive to combined pollutions photocatalytic removal and simultaneous H2 production and rhodamine B (RhB) degradation. The resulting NCDs/DCN performed much higher removal efficiency in different combined pollutions systems containing OFL/Cr (VI), BPA/Cr (VI) and CIP/Cr (VI) than in single system owing to the synergistic effect between organic pollution oxidation and Cr (VI) reduction. The free-radical quenching experiments, spectral technology and electron spin resonance (ESR) confirmed that Cr(VI) can be reduced by the conduction band (CB) electrons, and the h+ and O2− radicals dominated OFL degradation. The optimized NCDs/DCN displayed excellent simultaneously photocatalytic H2 production activity and RhB degradation with the H2 evolution rate of 3.68 μmol‧h−1‧g−1 and 100% RhB removal efficiency. The photocatalytic activity of simultaneous combined pollutions removal and synergistic H2 generation and RHB degradation provides a promising strategy for real wastewater remediation applications and energy utilization.

Phase controllable synthesis of Ni2+ post-modified CoP nanowire for enhanced oxygen evolution

Recently, tailor-made NiCo bimetallic phosphides hold a promising platform material in many fields such as catalysis and electrochemical energy storage and conversion. Typically, the traditional one-step phosphorization route offers limited phase control, with hexagonal phosphide phase structure (Ni2P type). Moreover, the phase component sensitively depends on the metal ratio to a great degree, posing great challenges to synthesize NiCo bimetallic phosphides with tuned composition and phase structure. Herein, we report a carbon encapsulated Ni2+ post-modified CoP nanowire (denoted as NiCoP@C) with single orthorhombic CoP phase structure and tuned Ni doping content via a facile & novel in-situ isomorphous-substitution method. More importantly, no any phase separation occurs, also further achieving a high Ni doping content (57 at%) that is less realized previously. As an example application, the as-made NiCoP@C nanowire exhibits excellent oxygen evolution reaction (OER) activity and stability, showing promising potential in the field of water splitting. The present novel strategy will pave the way for further phase controllable fabrication of bi/multi-metal-based materials in catalysis and energy storage & conversion fields.

Phosphorus-doped cobalt-iron oxyhydroxide with untrafine nanosheet structure enable efficient oxygen evolution electrocatalysis

Although explosive progresses have been achieved in the field of water splitting, the design and development of stable and inexpensive electrocatalysts for oxygen evolution remain a formidable challenge. Herein, the cost-efficient two dimensional (2D) phosphorus-doped CoFe oxyhydroxide nanosheets (denoted as CoFeP NSs) are successfully engineered and showing exceptional oxygen evolution reaction (OER) activity and chemical stability in 1 M KOH solution. This unique 2D nanosheet structure facilitates the mass transfer and electron transport, resulting in the remarkable OER activity that delivers a current density of 10 mA cm−2 at a low overpotential of 305 mV with an ultra-small Tafel slope 49.6 mV/dec. More significantly, the doped P also plays a vital role in modulating the surface active sites, leading to the substantial enhancement of electrocatalytic performances. Our study provides a facile one-pot method for the successful fabrication of 2D P-doped CoFe NSs which display superior electrocatalytic performance, shedding great promise for environment and energy-related fields.

Enhanced photoelectrochemical performance of defect-rich ReS2 nanosheets in visible-light assisted hydrogen generation

Defect introduction is one of the most important motivations to produce highly efficient electrocatalyst in the field of water splitting. Here we report the visible-light enhanced photoelectrochemical performance derived from defect-rich ReS2 nanosheets with high activity towards hydrogen generation from water. After continuous pre-electrolysis under visible-light irradiation for about 2 h, the activated ReS2 nanosheets electrocatalyst performs highly enhanced catalytic activity, with an onset potential decreasing from 170 to 88 mV and a long stability over 10 h. It is worth noting that only a small overpotential of 116 mV is required to afford the current density of 10 mA cm−2, which is the highest activity to date for ReS2 electrocatalysts and much better than most transition-metal dichalcogenide materials electrocatalysts. Ex-situ transmission electron microscopy (TEM) and inductively coupled plasma emission spectrometer (ICP) examinations demonstrate that the performance improvement is attributed to the defect introduction during the visible-light assisted pre-electrolysis process involving the rhenium atoms vacancies on the basal planes and the lattice fringes of ReS2. Theoretical calculations further confirm that the abundant Re atoms vacancies with lower Gibbs free energy for H adsorption activate the inert basal plane as highly active sites for hydrogen evolution.

A New Member of Electrocatalysts Based on Nickel Metaphosphate Nanocrystals for Efficient Water Oxidation.

High-performance electrocatalysts are desired for electrochemical energy conversion, especially in the field of water splitting. Here, a new member of phosphate electrocatalysts, nickel metaphosphate (Ni2 P4 O12 ) nanocrystals, is reported, exhibiting low overpotential of 270 mV to generate the current density of 10 mA cm-2 and a superior catalytic durability of 100 h. It is worth noting that Ni2 P4 O12 electrocatalyst has remarkable oxygen evolution performance operating in basic media. Further experimental and theoretical analyses demonstrate that N dopant boosts the catalytic performance of Ni2 P4 O12 due to optimizing the surface electronic structure for better charge transfer and decreasing the adsorption energy for the oxygenic intermediates.

Ag2S/Ag Heterostructure: A Promising Electrocatalyst for the Hydrogen Evolution Reaction.

Different metal chalcogenides, being a potential candidate for hydrogen evolution catalysts, have attracted enormous attention in the field of water splitting. In the present study, Ag2S/Ag is revealed as an efficient catalyst for hydrogen evolution. When a sacrificial template of the CuS nanostructure is used, Ag2S/Ag heterostructures are synthesized following a simple wet-chemical technique. Two different routes, wet chemical and hydrothermal, are followed to modulate the morphology of the CuS templates from flower ball to wirelike structures, which subsequently results in the formation of Ag2S nanostructure. Finally, the Ag layer is deposited on Ag2S with the help of a photoreduction technique. The unique heterostructure of Ag2S/Ag shows efficient catalytic activity in the H2 evolution reaction. A Ag2S/Ag wire can successfully generate a 10 mA/cm2 current density at a -0.199 V potential. Ag2S/Ag contains the micronanostructure where nanoplates of Ag2S/Ag assemble to give rise to microstructures such as flower balls and wire.

Recent Progress in Metal-Organic Frameworks for Applications in Electrocatalytic and Photocatalytic Water Splitting.

The development of clean and renewable energy materials as alternatives to fossil fuels is foreseen as a potential solution to the crucial problems of environmental pollution and energy shortages. Hydrogen is an ideal energy material for the future, and water splitting using solar/electrical energy is one way to generate hydrogen. Metal‐organic frameworks (MOFs) are a class of porous materials with unique properties that have received rapidly growing attention in recent years for applications in water splitting due to their remarkable design flexibility, ultra‐large surface‐to‐volume ratios and tunable pore channels. This review focuses on recent progress in the application of MOFs in electrocatalytic and photocatalytic water splitting for hydrogen generation, including both oxygen and hydrogen evolution. It starts with the fundamentals of electrocatalytic and photocatalytic water splitting and the related factors to determine the catalytic activity. The recent progress in the exploitation of MOFs for water splitting is then summarized, and strategies for designing MOF‐based catalysts for electrocatalytic and photocatalytic water splitting are presented. Finally, major challenges in the field of water splitting are highlighted, and some perspectives of MOF‐based catalysts for water splitting are proposed.

Targeted Synthesis of Unique Nickel Sulfide (NiS, NiS2) Microarchitectures and the Applications for the Enhanced Water Splitting System.

Water splitting is one of the ideal technologies to meet the ever increasing demands of energy. Many materials have aroused great attention in this field. The family of nickel-based sulfides is one of the examples that possesses interesting properties in water-splitting fields. In this paper, a controllable and simple strategy to synthesize nickel sulfides was proposed. First, we fabricated NiS2 hollow microspheres via a hydrothermal process. After a precise heat control in a specific atmosphere, NiS porous hollow microspheres were prepared. NiS2 was applied in hydrogen evolution reaction (HER) and shows a marvelous performance both in acid medium (an overpotential of 174 mV to achieve a current density of 10 mA/cm2 and the Tafel slope is only 63 mV/dec) and in alkaline medium (an overpotential of 148 mV to afford a current density of 10 mA/cm2 and the Tafel slope is 79 mV/dec). NiS was used in oxygen evolution reaction (OER) showing a low overpotential of 320 mV to deliver a current density of 10 mA/cm2, which is meritorious. These results enlighten us to make an efficient water-splitting system, including NiS2 as HER catalyst in a cathode and NiS as OER catalyst in an anode. The system shows high activity and good stabilization. Specifically, it displays a stable current density of 10 mA/cm2 with the applying voltage of 1.58 V, which is a considerable electrolyzer for water splitting.

Catalysts made of earth-abundant elements (Co, Ni, Fe) for water splitting: Recent progress and future challenges

This article reviews recent significant advances in the field of water splitting. Catalysts play very important roles in two half reactions of water splitting - water reduction and water oxidation. Considering potential future applications, catalysts made of cheap and earth abundant element(s) are especially important for economically viable energy conversion. This article focuses only on catalysts made of cobalt (Co), nickel (Ni) and iron (Fe) elements for water reduction and water oxidation. Different series of catalysts that can be applied in electrocatalytic and photocatalytic water spitting are discussed in detail and their catalytic mechanisms are introduced. Finally, the future outlook and perspective of catalysts made of earth abundant elements will be discussed.

Fast Water Oxidation Using Iron

Photolysis of water, a long-studied strategy for storing solar energy, involves two half-reactions: the reduction of protons to dihydrogen and the oxidation of water to dioxygen. Proton reduction is well-understood, with catalysts achieving quantum yields of 34% when driven by visible light. Water oxidation, on the other hand, is much less advanced, typically involving expensive metal centers and rarely working in conjunction with a photochemically powered system. Before further progress can be made in the field of water splitting, significant developments in the catalysis of oxygen evolution are needed. Herein we present an iron-centered tetraamido macrocyclic ligand (Fe-TAML) that efficiently catalyzes the oxidative conversion of water to dioxygen. When the catalyst is combined in unbuffered solution with ceric ammonium nitrate, its turnover frequency exceeds 1.3 s(-1). Real-time UV-vis and oxygen monitoring of the active complex give insights into the reaction and decay kinetics.