Bifunctional WS2@Co3S4 core-shell nanowire arrays for efficient water splitting

Co3S4/MnS p-p heterojunction as a highly efficient electrocatalyst for water splitting and electrochemical oxidation of organic molecules

In this work, Co3S4/MnS p-p heterojunction catalyst with hollow structure was successfully synthesized by one-step hydrothermal method. For oxygen evolution reaction (OER), urea oxidation reaction (UOR), lactate oxidation reaction (OER-LA) and glucose oxidation reaction (GOR), 1.59 V, 1.49 V, 1.54 V and 1.40 V vs. RHE are required to drive a current density of 50 mA cm-2, respectively, and the overpotential of hydrogen evolution reaction (HER) in 1 M KOH is 0.193 V at 50 mA cm-2. For the two-electrode overall water splitting in 1 M KOH, 1 M KOH containing 0.5 M urea, 1 M KOH containing 0.125 M lactate electrolyte and 1 M KOH containing 0.3 M glucose, water splitting voltages are only required at 1.73 V, 1.60 V, 1.62 V and 1.63 V to drive the current density of 50 mA cm-2. Moreover, its activity does not attenuate significantly in 1 M KOH containing 0.125 M lactate after continuous operation at 50 mA cm-2 for 200 h, showing excellent durability. In addition, the technology of glucose oxidation assisted water splitting for hydrogen production has been preliminarily explored, which also has excellent HER performance. Density functional theory (DFT) show that the p-p heterojunction between Co3S4 and MnS is conducive to the redistribution of electrons at the interface, thus promoting electron migration. Finally, the water splitting cell coupled with lactic acid oxidation reaction using polylactic acid pipette as source also exhibits high activity and stability. This study provides another idea and strategy for hydrogen production while waste plastic treatment.

Constructing WS2/WO3-x heterostructured electrocatalyst enriched with oxygen vacancies for accelerated hydrogen evolution reaction

H2 produced through hydrogen evolution reaction (HER) is a shining star in the field of clean energy. Significant efforts have been dedicated to develop efficient and stable electrocatalysts to reduce the energy barrier and accelerate the kinetics of Hydrogen evolution reaction (HER) under various environments. Herein, we propose a strategy to accelerate the kinetics of HER under acid and alkaline environments by combining heterostructure engineering with defect engineering. We have successfully synthesized a series of WS2/WO3-x heterostructured catalysts, accompanied with substantial oxygen vacancies using a two-step synthesis method. With the partially sulfurization of WO3-x, the heterojunction interface of WS2 and WO3-x was formed along with the appearance of oxygen vacancies, which can facilitate the migration of electrons. The heterostructured catalyst enriched with oxygen vacancies (defined as WS2/WO3-x-2) demonstrates superior HER performance in acidic and alkaline electrolytes. At a current density of 10 mA cm-2, the WS2/WO3-x-2 heterostructured catalyst manifests an overpotential of 120 mV in the acidic electrolytes and a slightly higher overpotential of 150 mV in an alkaline environment. The overpotentials offer an improvement compared to reported W-based catalysts in terms of HER performance. This work provides guiding significance on the design of heterostructured catalysts with promising performance for HER in acidic and alkaline environments.

Novel Heterostructure-Based CoFe and Cobalt Oxysulfide Nanocubes for Effective Bifunctional Electrocatalytic Water and Urea Oxidation

The development of effective oxygen evolution reaction (OER) and urea oxidation reaction (UOR) on heterostructure electrocatalysts with specific interfaces and characteristics provides a distinctive character. In this study, heterostructure nanocubes (NCs) comprising inner cobalt oxysulfide (CoOS) NCs and outer CoFe (CF) layered double hydroxide (LDH) are developed using a hydrothermal methodology. During the sulfidation process, the divalent sulfur ions (S2-) are released from the breakdown of the sulfur source and react with the Co-precursors on the surface leading to the transformation of CoOH nanorods into CoOS nanocubes. Further, X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) analyses reveal that the interactions at the interface of the CF@CoOS NCs significantly altered the electronic structure, thus enhancing the electrocatalytic performance. The optimal catalysts exhibited effective OER and UOR activities, the attained potentials are 1.51 and 1.36 V. This remarkable performance is attributable to the induction of electron transfer from the CoFe LDH to CoOS, which reduces the energy barrier of the intermediates for the OER and UOR. Furthermore, an alkaline water and urea two-cell electrolyzer assembled using CF@CoOS-2 NCs and Pt/C as the anode and cathode requires a cell voltage of 1.63 and 1.56 V along with a durability performance.

Interfacial and Electronic Modulation of W Bridging Heterostructure Between WS2 and Cobalt-Based Compounds for Efficient Overall Water Splitting

The development of high performance electrocatalysts for effective hydrogen production is urgently needed. Herein, three hybrid catalysts formed by WS2 and Co-based metal-organic frameworks (MOFs) derivatives are constructed, in which the small amount of W in the MOFs derivatives acts as a bridge to provide the charge transfer channel and enhance the stability. In addition, the effects of the surface charge distribution on the catalytic performance are fully investigated. Due to the optimal interfacial electron coupling and rearrangement as well as its unique porous morphology, WS2 @W-CoPx exhibits superior bifunctional performance in alkaline media with low overpotentials in hydrogen evolution reaction (HER) (62 mV at 10 mA cm-2 ) and oxygen evolution reaction (OER) (278 mV at 100 mA cm-2 ). For overall water splitting (OWS), WS2 @W-CoPx only requires a cell voltage of 1.78 V at 50 mA cm-2 and maintains good stability within 72 h. Density functional theory calculations verify that the combination of W-CoPx with WS2 can effectively enhance the activity of OER and HER with weakened OH (or O) adsorption and enhanced H atom adsorption. This work provides a feasible idea for the design and practical application of WS2 or phosphide-based catalysts in OWS.

Skeleton-coated CoCu-Based bimetal hollow nanoprisms as High-Performance electrocatalysts for oxygen evolution reaction

CoSx materials with high catalytic activity are considered as promising HER electrocatalysts, but their inherent low electrical conductivity and easy loss of active sites have greatly limited their applications in OER electrocatalysis. Herein, we present a convenient method to synthesize Co-Cu hollow nanoprisms after wrapping and calcining with trithiocyanuric acid (C3H3N3S3) (denoted N-Co-Cu-S-x HNs). The results showed that Cu doping modified the charge density of Co center, leading to the enhancement of the intrinsic activity of the Co3S4 active center, meanwhile wrapping trithiocyanuric acid on the surfaces and calcinating to form N-containing C skeleton as a flexible substrate to encapsulate the catalysts, which effectively protected the active sites inside the catalysts. Notably, the OER catalyst that was optimized by adjusting the metal ratio and controlling the trithiocyanuric acid incorporation exhibited a low overpotential of 306 mV under a current density of 10 mA cm-2 and showed a superior durability of more than 27 h. This work may provide some insights into the preparation of oxygen evolution reaction catalysts with excellent performance through doping transition metals and protecting the internal active sites strategies.