Enhancing the catalytic OER performance of MoS2via Fe and Co doping

Cobalt nanoparticles intercalation coupled with tellurium-doping MXene for efficient electrocatalytic water splitting

Nowadays, the inherent re-stacking nature and weak d-p hybridization orbital interactions within MXene remains significant challenges in the field of electrocatalytic water splitting, leading to unsatisfactory electrocatalytic activity and cycling stability. Herein, this work aims to address these challenges and improve electrocatalytic performance by utilizing cobalt nanoparticles intercalation coupled with enhanced π-donation effect. Specifically, cobalt nanoparticles are integrated into V2C MXene nanosheets to mitigate the re-stacking issue. Meanwhile, a notable charge redistribution from cobalt to vanadium elevates orbital levels, reduces π*-antibonding orbital occupancy and alleviates Jahn-Teller distortion. Doping with tellurium induces localized electric field rearrangement resulting from the changes in electron cloud density. As a result, Co-V2C MXene-Te acquires desirable activity for hydrogen evolution reaction and oxygen evolution reaction with the overpotential of 80.8 mV and 287.7 mV, respectively, at the current density of -10 mA cm-2 and 10 mA cm-2. The overall water splitting device achieves an impressive low cell voltage requirement of 1.51 V to obtain 10 mA cm-2. Overall, this work could offer a promising solution when facing the re-stacking issue and weak d-p hybridization orbital interactions of MXene, furnishing a high-performance electrocatalyst with favorable electrocatalytic activity and cycling stability.

Hydrothermally Synthesized rGO/MnO2/MoS2 Nanohybrids as Superior Bifunctional Electrocatalysts for Oxygen and Hydrogen Evolution Reactions

This investigation delved into the field of bifunctional electrocatalyst water splitting, aimed at advancing sustainable energy by addressing the scarcity of efficient nonprecious electrocatalysts capable of facilitating both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). This study focused on nanohybrids consisting of hydrothermally synthesized rGO/MnO2/MoS2 composites and highlighted their efficacy as bifunctional electrocatalysts. The synergistic integration of rGO/MnO2/MoS2 enhanced the surface area, magnified electroactive sites, established a customized conductive arrangement, and provoked the efficiency in splitting of water. The nanohybrid displayed exceptional catalytic performance for the OER and HER, with significantly reduced overpotentials of 208 and 205 mV in 1 M KOH at 10 mA cm-2 current density, respectively. The findings underscore the potential of these cost-effective and environmentally friendly rGO/MnO2/MoS2 nanohybrids in advancing the field of electrocatalysis for renewable energy applications.

Stability of Multivalent Ruthenium on CoWO4 Nanosheets for Improved Electrochemical Water Splitting with Alkaline Electrolyte

Engineering low-cost electrocatalysts with desired features is vital to decrease the energy consumption but challenging for superior water splitting. Herein, we development a facile strategy by the addition of multivalence ruthenium (Ru) into the CoWO4/CC system. During the synthesis process, the most of Ru3+ ions were insinuated into the lattice of CoWO4, while the residual Ru3+ ions were reduced to metallic Ru and further attached to the interface between carbon cloth and CoWO4 sheets. The optimal Ru2(M)-CoWO4/CC exhibited superior performance for the HER with an overpotential of 85 mV@10 mA cm-2, which was much better than most of reported electrocatalysts, regarding OER, a low overpotential of 240 mV@10 mA cm-2 was sufficient. In comparison to Ru2(0)-CoWO4/CC with the same Ru mass loading, multivalence Ru2(M)-CoWO4/CC required a lower overpotential for OER and HER, respectively. The Ru2(M)-CoWO4/CC couple showed excellent overall water splitting performance at a cell voltage of 1.48 V@10 mA cm-2 for used as both anodic and cathodic electrocatalysts. Results of the study showed that the electrocatalytic activity of Ru2(M)-CoWO4/CC was attributed to the in-situ transformation of Ru/Co sites, the multivalent Ru ions and the synergistic effect of different metal species stimulated the intrinsic activity of CoWO4/CC.

Real-time screening of NixBy bifunctional electrocatalysts for overall NH3 synthesis via SG-TC SECM

Electrochemical ammonia synthesis, which couples oxygen evolution at the anode with nitrogen reduction at the cathode, holds great significance for future food and energy needs. Both of these half-cell reactions determine the overall cell potential and efficiency of the process. However, the employment of different catalysts on either side, due to discrete mechanisms, increases the complexity and material processing costs of the system, where the designing of a bifunctional catalyst active towards both the NRR and OER is of huge significance. Unfortunately, the initial screening of the designed catalysts via physical characterizations, optical methods and other techniques, does not provide details about the electrochemical activity. The scanning electrochemical microscopy (SECM) technique can be useful to screen multi-catalysts at the same time for their electrochemical activities. Herein, we employed the sample generation-tip collection (SG-TC) mode of SECM to screen the designed NixBy catalysts before half-cell investigations, which suggested that the catalyst synthesized via sonochemical reduction (SR), i.e. NixBy (SR), was a better catalyst. This inference was in accordance with the half-cell NRR and OER measurements (FE: 49% for NH3 production, OER overpotential: 300 mV). By virtue of this remarkable bifunctional activity, the NRR-OER coupled full cell was assembled, which initiated the NH3 production at just 1.7 V and produced NH3 (1.08 mg h-1 mgcat-1) at the cathode and O2 (0.81 mg h-1 mgcat-1) at the anode after 2 h of electrolysis at 1.9 V.

Cr doping and heterostructure-accelerated NiFe LDH reaction kinetics assist the MoS2 oxygen evolution reaction

Although molybdenum disulfide (MoS2) has garnered significant interest as a potential catalyst for the oxygen evolution reaction (OER), its poor intrinsic activity and few marginal active spots restrict its electrocatalytic activity. Herein, we successfully constructed a catalyst via a simple hydrothermal method by forming a heterostructure of MoS2 with Cr-doped nickel-iron hydroxide (NiFe LDH) to synthesize a MoS2/NiFeCr LDH catalyst to significantly improve the OER catalytic performance. MoS2 plays a crucial function as an electron transport channel in the MoS2/NiFeCr LDH heterostructure, which increases the electron transport rate. Furthermore, a larger active surface area for NiFeCr LDH is provided by the ultrathin layered structure of MoS2, increasing the number of active sites and encouraging the OER. On the other hand, the introduction of Cr element increased the density of the catalytic center and provided additional Cr-OH active sites, which accelerated the oxygen decomposition reaction. These two factors act synergistically to improve the intrinsic structure of MoS2, increase the number of reactive sites, and dramatically enhance the OER catalytic performance. Excellent OER activity is demonstrated by the MoS2/NiFeCr LDH catalyst, which only needs an overpotential of 224 mV to obtain a current density of 10 mA cm-2 and a Tafel slope of 61 mV dec-1. The catalyst also demonstrated outstanding stability, with its activity practically holding steady after 48 h of testing. This work offers novel ideas for enhancing and designing MoS2-based OER catalysts, and it provides a crucial reference for research in the field of clean energy.

Construction active sites in nickel sulfide by dual-doping vanadium/cobalt for highly effective oxygen evolution reaction

Rational design and exploration of oxygen evolution reaction (OER) electrocatalysts with exceptional performance are crucial for the advancement of the hydrogen energy economy. In this study, vanadium/cobalt (V/Co) dual-doped nickel sulfide (Ni3S2) nanowires were synthesized on a nickel foam (NF) substrate to overcome the sluggish kinetics typically associated with OER. The resulting catalyst exhibited outstanding electrocatalytic activity towards OER in a 1.0 M KOH electrolyte, with a minimal overpotential of 155 and 263 mV, the current densities of 10 and 100 mA cm-2 can be achieved effortlessly. Importantly, this catalyst demonstrated remarkable stability over extended periods, maintaining its performance for 25 h under constant current density, 55 h under continuously varying current density, and even after undergoing 2000 cycles of cyclic voltammetry (CV), which had surpassed those of most non-noble metal electrocatalysts. The X-ray photoelectron spectroscopy and density functional theory analyses confirmed that the co-doping of Co and V redistributed the electron of Ni, leading to improvements in the d-band center, structural characteristics, and free energy landscapes of adsorbed intermediates. This work presents a novel strategy, based on the connection between electronic structure and catalytic properties, in the design of double-doped catalysts for efficient OER.

Realizing a high OER activity in new single-atom catalysts formed by introducing TMNx (x = 3 and 4) units into carbon nanotubes using high-throughput calculations

Exploring highly efficient electrocatalysts for the oxygen evolution reaction (OER) is of great significance for hydrogen production through water splitting. By means of high-throughput density functional theory (DFT) calculations, we investigated the OER catalytic activity of a series of one-dimensional carbon nanotube (CNT)-based systems containing TMN4 or TMN3 functional units. Through the screening of 3d/4d/5d transition metals (TMs) from Group IVB to Group VIII, eight newly obtained TMNx@CNT (x = 3 and 4) systems were found to exhibit excellent OER activity, with very low overpotentials in the range 0.29-0.51 V, where the Co, Rh, Ir, Ti, Fe, and Ru atoms could be used as active sites. It was found that under the framework of TMN3@CNTs, the pre-adsorption of some species from water dissociation on the relevant TM sites (TM = Ti, Fe, and Ru) could lead to a high OER catalytic activity, which was different from the general situation where OER reactions directly occur on the clean surfaces of the remaining systems with Co/Rh/Ir metal centers. Moreover, the catalytic mechanisms were analyzed in detail. This work can be conducive to obtaining low-cost and high-performance OER single-atom electrocatalysts based on excellent CNT nanomaterials.

Heterogeneous Electrocatalytic Oxygen Evolution Reaction by a Sol-Gel Electrode with Entrapped Na3 [Ru2 (μ-CO3 )4 ]: The Effect of NaHCO3

The Na3 [Ru2 (μ-CO3 )4 ] complex is acting as a water oxidation catalyst in a homogeneous system. Due to the significance of heterogeneous systems and the effect of bicarbonate on the kinetic, we studied the bicarbonate effect on the heterogeneous electrocatalyst by entrapping the Na3 [Ru2 (μ-CO3 )4 ] complex in a sol-gel matrix. We have developed two types of sol-gel electrodes, which differ by the precursor, and are demonstrating their stability over a minimum of 200 electrochemical cycles. The pH increases affected the currents and kcat for both types of electrodes, and their hydrophobicity, which was obtained from the precursor type, influenced the electrocatalytic process rate. The results indicate that NaHCO3 has an important role in the catalytic activity of the presented heterogeneous systems; without NaHCO3 , the diffusing species is probably OH- , which undergoes diffusion via the Grotthuss mechanism. To the best of our knowledge, this is the first study to present a simple and fast one-step entrapment process for the Na3 [Ru2 (μ-CO3 )4 ] complex by the sol-gel method under standard laboratory conditions. The results contribute to optimizing the WSP, ultimately helping expand the usage of hydrogen as a green and more readily available energy source.

An advanced PdNPs@MoS2 nanocomposite for efficient oxygen evolution reaction in alkaline media

In response to the increasing availability of hydrogen energy and renewable energy sources, molybdenum disulfide (MoS2)-based electrocatalysts are becoming increasingly important for efficient electrochemical water splitting. This study involves the incorporation of palladium nanoparticles (PdNPs) into hydrothermally grown MoS2via a UV light assisted process to afford PdNPs@MoS2 as an alternative electrocatalyst for efficient energy storage and conversion. Various analytical techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDS), were used to investigate the morphology, crystal quality, and chemical composition of the samples. Although PdNPs did not alter the MoS2 morphology, oxygen evolution reaction (OER) activity was driven at considerable overpotential. When electrochemical water splitting was performed in 1.0 M KOH aqueous solution with PdNPs@MoS2 (sample-2), an overpotential of 253 mV was observed. Furthermore, OER performance was highly favorable through rapid reaction kinetics and a low Tafel slope of 59 mV dec-1, as well as high durability and stability. In accordance with the electrochemical results, sample-2 showed also a lower charge transfer resistance, which again provided evidence of OER activity. The enhanced OER activity was attributed to a number of factors, including structural, surface chemical compositions, and synergistic effects between MoS2 and PdNPs.

Chemically Etched Prussian Blue Analog-WS2 Composite as a Precatalyst for Enhanced Electrocatalytic Water Oxidation in Alkaline Media

The electrochemical water-splitting reaction is a promising source of ecofriendly hydrogen fuel. However, the oxygen evolution reaction (OER) at the anode impedes the overall process due to its four-electron oxidation steps. To address this issue, we developed a highly efficient and cost-effective electrocatalyst by transforming Co-Fe Prussian blue analog nanocubes into hollow nanocages using dimethylformamide as a mild etchant and then anchoring tungsten disulfide (WS2) nanoflowers onto the cages to boost OER efficiency. The resulting hybrid catalyst-derived oxide demonstrated a low overpotential of 290 mV at a current density of 10 mA cm-2 with a Tafel slope of 75 mV dec-1 in 1.0 M KOH and a high faradaic efficiency of 89.4%. These results were achieved through the abundant electrocatalytically active sites, enhanced surface permeability, and high electronic conductivity provided by WS2 nanoflowers and the porous three-dimensional (3D) architecture of the nanocages. Our research work uniquely combines surface etching of Co-Fe PBA with WS2 growth to create a promising OER electrocatalyst. This study provides a potential solution to the challenge of the OER in electrochemical water-splitting, contributing to UN SDG 7: Affordable and clean energy.

External Fields Assisted Highly Efficient Oxygen Evolution Reaction of Confined 1T-VSe2 Ferromagnetic Nanoparticles

As a clean and effective approach, the introduction of external magnetic fields to improve the performance of catalysts has attracted extensive attention. Owing to its room-temperature ferromagnetism, chemical stability, and earth abundance, VSe2 is expected to be a promising and cost-effective ferromagnetic electrocatalyst for the accomplishment of high-efficient spin-related OER kinetics. In this work, a facile pulsed laser deposition (PLD) method combined with rapid thermal annealing (RTA) treatment is used to successfully confine monodispersed 1T-VSe2 nanoparticles in amorphous carbon matrix. As expected, with external magnetic fields of 800 mT stimulation, the confined 1T-VSe2 nanoparticles exhibit highly efficient oxygen evolution reaction (OER) catalytic activity with an overpotential of 228 mV for 10 mA cm-2 and remarkable durability without deactivation after >100 h OER operation. The experimental results together with theoretical calculations illustrate that magnetic fields can facilitate the surface charge transfer dynamics of 1T-VSe2 , and modify the adsorption-free energy of *OOH, thus finally improving the intrinsic activity of the catalysts. This work realizes the application of ferromagnetic VSe2 electrocatalyst in highly efficient spin-dependent OER kinetics, which is expected to promote the application of transition metal chalcogenides (TMCs) in external magnetic field-assisted electrocatalysis.