Hydrogen Evolution Kinetics Research Articles

Impact of Double Layer on Electrochemical Kinetics via Bottom up Multiscale Modeling Approach

Electric double layers (EDLs) play a fundamental role in various electrochemical processes such as colloidal dispersions, surface charging, and charge-transfer reactions. Increasingly, the role of EDLs on reaction kinetics is being studied[1], revealing their importance in predicting the intrinsic and electrolyte-dependent kinetics of electrochemical reactions. Despite the extensive history of EDL modeling, there remain challenges in predicting the impact of EDL structure on reaction kinetics. The characteristic length of EDL for non-dilute solutions (typically 10 – 100 nanometers) exceeds the grasp of regular ab initio molecular dynamics (AIMD) simulations. While continuum models offer a means to estimate the quasi-equilibrium structure of EDLs with substantially lower computational cost than molecular dynamics, conventional continuum models require parameter fitting[2] due to their lack of appropriate expressions for microscopic interactions. Furthermore, the lack of a commonly accepted micro-kinetic model to evaluate the role of the EDL structure on the reaction kinetics prevents the optimization of the interface for improved reaction rates.In this talk, we propose a novel modeling framework for analyzing micro-kinetics that accounts for the contributions of EDL structure by leveraging our recently developed continuum EDL model [3] and density functional theory (DFT) calculations. Our previous work showed that the continuum model can accurately predict differential capacitance for EDL charging without necessitating parameter-fitting by incorporating microscopic interactions such as electron spillover, entropy due to solute size variation, and polarization of solvent and solute molecules [3]. We refine the continuum EDL model to account for the interactions between adsorbate coverage and EDL structure. This model utilizes DFT results, i.e., free energies and charge distributions of the adsorbates at potential of zero charge, as input properties. The model calculates the adsorbates’ coverage to minimize the total grand potential, while accounting for both the effect of electrostatic potential on the adsorbate free energy and the effect of adsorbate charge density on the electrostatic potential simultaneously. The transition state of the rate determining step is treated as an adsorbate species, with its coverage evaluated in the same manner as the other adsorbates, which is used to evaluate the reaction rate based on transition state theory. This model framework enables us to evaluate the intrinsic and electrolyte-dependent kinetic activity with reasonable computational resources. Finally, we apply this model to investigate the kinetics of hydrogen evolution and oxidation reactions (HER/HOR) having favorable comparisons with measured cation- and pH- dependent kinetics[4]. The results suggest that the charge distribution of the transition state can significantly affect electrolyte-dependent kinetics of electrochemical reactions, highlighting the importance of further analyzing the effects of EDL structures on reaction kinetics. Acknowledgements: This work was partially supported by the by the Center for Ionomer-based Water Electrolysis (CIWE), a DOE sponsored Energy Earthshot Research Center under contract number DE-AC02-05CH11231, and by a CRADA with Toyota Central R&D Labs., Inc. Part of this work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. The authors acknowledge the HydroGen Energy Materials Network from the Department of Energy, Hydrogen and Fuel Cell Technologies Office for funding under Contract numbers DE-AC02-05CH11231. Reference: [1] Shin, S.J., et al., On the importance of the electric double layer structure in aqueous electrocatalysis. Nat Commun, 2022. 13(1): p. 174.[2] Huang, J., Density-Potential Functional Theory of Electrochemical Double Layers: Calibration on the Ag(111)-KPF(6) System and Parametric Analysis. J Chem Theory Comput, 2023. 19(3): p. 1003-1013.[3] Shibata, M., S., et al., Parameter-fitting-free Continuum Modeling of Electrical Double Layer in Aqueous Electrolyte, Submitted.[4] Huang, B., et al., Cation- and pH-Dependent Hydrogen Evolution and Oxidation Reaction Kinetics. JACS Au, 2021. 1(10): p. 1674-1687. Figure 1

Theoretical Studies of Hydrogen Evolution Involving Imidazolium Proton Donors

The hydrogen evolution reaction (HER) is an important electrocatalytic reaction used for the electrochemical production of hydrogen gas. Its reverse reaction, the hydrogen oxidation reaction, is used to produce protons used in electrocatalytic reduction reactions for various electrochemical energy conversion and storage applications. While many fundamental studies have analyzed interfacial reactivity in aqueous HER, analogous mechanistic understanding of HER reactivity in nonaqueous media remains limited.In this presentation, periodic density functional theory (DFT) calculations are applied to mechanistic studies of HER on Pt(111) using various imidazolium proton donors. These studies incorporate analyses of imidazole adsorption and potential-dependent activation energies. The conjugate bases of imidazole adsorb strongly to the electrode surface. Yet, the adsorption geometries and energetics are sensitive to substituent effects and isomeric configurations at the interface. The potential-dependent binding geometries and adsorption energies of different imidazoles adsorbed to Pt(111) are analyzed in a dielectric continuum implicit solvent. These calculations demonstrate how imidazole derivatization and electrode surface charge impact the adsorption of imidazole conjugate bases during HER. To gain insights into the kinetics of the elementary Volmer and Heyrovsky steps of HER, potential-dependent reaction energies and activation barriers were calculated using the charge extrapolation method. Energetics were calculated for different electrode potentials by modifying the coverage of protons. This approach was used to develop relationships between reaction thermodynamics and kinetics via Brønsted–Evans–Polanyi relationships for various imidazoles, where this relationship gives charge transfer coefficients in the Butler–Volmer equation. The goal of assessing these reaction parameters is to enhance understanding of charge transfer processes and molecular interactions at the electrode-electrolyte interface, which is essential for the design of high-efficiency energy conversion and storage devices. The potential-dependent adsorption behavior and kinetics of elementary proton-coupled electron transfer steps are used to understand the reaction kinetics of hydrogen evolution in a nonaqueous imidazole-based electrolyte through comparisons to voltammetry measurements. Through these analyses, we identify kinetic trends across functionalized imidazoles, providing valuable perspectives for the development of catalytic systems and energy storage technologies.

Strong electronic coupling of graphdiyne/CuCo2S4 ohmic junction for boosting photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution is a clean energy technology with sustainable potential. Effective electronic coupling is a crucial approach to enhance hydrogen evolution kinetics. In this work, graphdiyne (GDY) nanosheets were successfully synthesized utilizing a ball-milling-assisted reduction and elimination method, and subsequently coupled with 3D hierarchical CuCo2S4 microflowers forming ohmic junction GDY/CuCo2S4 (GCC) with robust electronic coupling effects. The uniformly distributed pore canal of GDY endow GCC with a substantial specific surface area. The unique porous hierarchical of CuCo2S4 facilitates extensive interaction with solutes, thereby enhancing proton absorption capacity. DFT calculations reveal a robust electronic coupling interface between GDY and CuCo2S4, which increases the local electron density of GDY. In-situ XPS confirms the successful construction of the ohmic junction, which induces electron transfer from GDY to CuCo2S4, thereby suppressing electron-hole recombination in GDY and enhancing photocatalytic hydrogen evolution activity. Consequently, GCC-25 achieved optimal photocatalytic hydrogen evolution activity at 6899.24 μmol h⁻¹ g⁻¹, which is 5.55 and 4.48 times higher than that of pristine GDY and CuCo2S4, respectively. This work provides a novel approach for constructing GDY-based 3D hierarchical ohmic junctions to enhance photocatalytic hydrogen evolution performance.

A "Two-Pronged" Strategy to Boost Hydrogen Evolution Kinetics on NiFe-Based (Oxy)hydroxides via Oxygen Deficient Ni-Mo-Fe Coordinate Structures for Ultra-Stable Ampere-Level Alkaline Overall Water Splitting.

NiFe (oxy)hydroxides have been regarded as one of the state-of-the-art catalysts for oxygen evolution reaction (OER). Unfortunately, the sluggish hydrogen evolution reaction (HER) kinetics limit its application as bifunctional electrocatalyst for alkaline overall water splitting (OWS). Herein, a "two-pronged" strategy is proposed to construct highly active oxygen deficient Ni-Mo-Fe coordinate structures in NiFe (oxy)hydroxide (NFM-OVR/NF), which simultaneously reduces the energy barrier of Volmer and Heyrovsky steps during alkaline HER process and significantly accelerate the reaction kinetics. Consequently, NFM-OVR/NF delivers overpotentials as low as 25 and 234mV to achieve 10 and 1000mA cm-2 in 1.0M KOH, respectively. Furthermore, benefiting from excellent HER and OER activity, NFM-OVR/NF exhibits a remarkable OWS activity with cell voltages of 1.44V and 1.77V at 10 and 1000mA cm-2 in 1.0M KOH, and displays ultralong-term stability for 600h at 500mA cm-2, while remaining durable for 300h in an alkaline water electrolyzer in 30% KOH at 80°C. The calculated price per gallon of gasoline equivalent for the produced H2 is $ 0.92, which is much lower than 2026 U.S. Department of Energy target ($ 2.00), demonstrating feasibility and practicability of NFM-OVR/NF for industrial applications.

Vanadium-Doped Heterointerfaced Ni3N-MoOx Nanosheets with Optimized H and H2O Adsorption for Effective Alkaline Hydrogen Electrocatalysis.

Nickel (Ni)-based materials represent a compelling avenue as platinum alternatives in the realm of alkaline hydrogen electrocatalysis. However, conventional nickel nitrides (Ni3N) have long been hindered by sluggish hydrogen evolution kinetics in alkaline environments, owing to inadequate adsorption strengths of both hydrogen and water molecules. Herein, a novel approach is presented involving the design of vanadium (V)-doped Ni3N/MoOx heterogeneous nanosheets (V-Ni3N@MoOx), engineered to achieve optimized adsorption strengths for hydrogen evolution and oxidation reactions (HER/HOR). Theoretical insights underscore the superior catalytic performance of this composite, attributed to a synergistic interplay between unique V doping and the heterointerfaced structure. This synergistic effect not only fine-tunes the electronic structure, establishing an optimal d band center to mitigate proton over-bonding, but also ameliorates the energy barrier through enhanced H2O dissociation capability. Consequently, V-Ni3N@MoOx manifests remarkable catalytic activities, evincing an overpotential of 56mV at 10mAcm-2 for HER and an exchange current density of 1.91mAcm-2 for HOR in alkaline media. Notably, the stability assessment reveals the enduring performance of V-Ni3N@MoOx for HER/HOR, exhibiting no activity decay over extended operational durations. This study underscores the efficacy of heterogeneous interface modulation as a transformative strategy in designing Ni-based materials for alkaline hydrogen electrocatalysis.

Manipulating nano-WS2 aggregates in electroplated Ni coating to mitigate hydrogen embrittlement in X70 pipeline steel

WS2 is a two-dimensional nanomaterial with significant potential for hydrogen barrier applications. Herein, WS2/Ni composite coatings were fabricated on X70 pipeline steel substrates via electrodeposition. The properties of the composite coatings were systematically examined by electrochemical hydrogen permeation tests, hydrogen evolution kinetics tests, SSRT, SKPFM, and FEM. The results indicate that varying the deposition time leads to changes in coating microstructure, which correspondingly influence hydrogen permeation performance. Furthermore, the hydrogen barrier mechanism of the WS2/Ni composite coatings involves two key processes: the inhibition of hydrogen evolution reactions on the coating surface and hydrogen adsorption by WS2 within the coating interior.

Optimizing H-adsorption affinity on electron-enriched Pdδ- active sites for efficient photocatalytic H2 evolution

Noble metal Pd is a promising H2-evolution cocatalyst and has attracted expansive attention in photocatalytic water splitting. However, the present H2-production rate of Pd cocatalysts is still limited due to its strong hydrogen adsorption on Pd active sites, resulting in poor hydrogen evolution kinetics. In this work, an electron-enriched Pdδ- modulation strategy is developed to weaken the hydrogen adsorption on Pd active sites by producing PdAu alloy, resulting in an increased H2-production rate. In this case, the PdAu homogeneous alloy with a particle size of 9–20 nm is uniformly deposited on the TiO2 surface to produce PdAu-modified TiO2 photocatalysts (TiO2/PdAu). It is found that the prepared TiO2/Pd79Au21 sample achieves the maximal photocatalytic H2-production performance of 31.98 mmol g-1 h−1, which is 1.53 times higher than that of TiO2/Pd photocatalyst. Experimental and theoretical studies show that in addition to the promoted transfer of photogenerated carriers, the PdAu alloy can spontaneously induce the electron transfer from Au to Pd to form electron-enriched Pdδ- sites, which prominently weakens the Pd-Hads bonds and thus improve the H2-production efficiency. This study provides further insight into the rational optimization of active sites to facilitate the design of efficient photocatalysts.

Boosting Acidic Hydrogen Evolution Kinetics Induced by Weak Strain Effect in PdPt Alloy for Proton Exchange Membrane Water Electrolyzers.

Strain engineering is an effective strategy for manipulating the electronic structure of active sites and altering the binding strength toward adsorbates during the hydrogen evolution reaction (HER). However, the effects of weak and strong strain engineering on the HER catalytic activity have not been fully explored. Herein, the core-shell PdPt alloys with two-layer Pt shells (PdPt2L) and multi-layer Pt shells (PdPtML) is constructed, which exhibit distinct lattice strains. Notably, PdPt2L with weak strain effect just requires a low overpotential of 18mV to reach 10mA cm-2 for the HER and shows the superior long-term stability for 510h with negligible activity degradation in 0.5M H2SO4. The intrinsic activity of PdPt2L is 6.2 and 24.5 times higher than that of PdPtML and commercial Pt/C, respectively. Furthermore, PdPt2L||IrO2 exhibits superior activity over Pt/C||IrO2 in proton exchange membrane water electrolyzers and maintains stable operation for 100h at large current density of 500mA cm-2. In situ/operando measurements verify that PdPt2L exhibits lower apparent activation energy and accelerated ad-/desorption kinetics, benefiting from the weak strain effect. Density functional theory calculations also reveal that PdPt2L displays weaker H* adsorption energy compared to PdPtML, favoring for H* desorption and promoting H2 generation.

Modulating d-p-band electron coupling by N-doping for promoting CuSAs-N/TiO2 photocatalytic hydrogen evolution

Doping can effectively improve the light absorption of single-atoms photocatalysts, but the metal-support interaction (MSI) and surface electronic structure will change due to doping, which needs further study. Herein, we report a nano-TiO2 co-modified with internal doping of N and surface loading of Cu single atoms (CuSAs-N/TiO2) for photocatalytic water-splitting hydrogen evolution. Experimental and theoretical studies confirm that the internal doped N can interact strongly with the surface-loaded CuSAs by modulating the d-p-band electronic coupling. The enhancement of d-p-band electronic coupling enhances the strong electron interaction between CuSA and support of N-doped TiO2. Especially, it significantly affects the d-p-band electronic structure of the catalyst surface lattice and causes electron redistribution in the local structure of surface CuSAs, which can optimize the surface hydrogen evolution kinetics and promote hydrogen production. Consequently, the photocatalytic hydrogen evolution activity, photoelectric response rate and light energy utilization of CuSAs-N/TiO2 are significantly improved. This work reveals the fundamental necessity of d-p-band electron coupling in MSI and catalyst surface electronic structure for driving solar water splitting. It provides valuable insights for the rational design of metal single-atom photocatalysts with high activity and efficient light energy utilization.

Fe-Induced Surface Regulation and Accelerated Hydrogen Evolution Kinetics in γ-MnS Three-Dimensional Microarchitectures

Fe-Induced Surface Regulation and Accelerated Hydrogen Evolution Kinetics in γ-MnS Three-Dimensional Microarchitectures

Rationally designed CaTiO3/Mn0.5Cd0.5S/Ni3C S-scheme/Schottky integrated heterojunction for efficient photocatalytic H2 evolution

Developing effective photocatalysts to achieve stable and efficient solar-induced hydrogen production remains a significant challenge due to rapid photocarrier recombination and sluggish hydrogen evolution kinetics. Here, a multi-interfacial engineering strategy involving the decoration of metallic Ni3C onto CaTiO3/Mn0.5Cd0.5S was proposed to create an S-scheme/Schottky hybrid heterostructure with multiple carrier transport paths for effective photocatalytic H2 production. Exploiting the synergy between S-scheme heterojunction and Schottky barrier, the engineered ternary CaTiO3/Mn0.5Cd0.5S/Ni3C hybrid heterojunction exhibits outstanding photostability and significantly enhanced hydrogen evolution activity of 79.1 mmol g-1 h−1, which was about 4.55, 3.22 and 2.59 times greater than Mn0.5Cd0.5S, Mn0.5Cd0.5S/Ni3C, and CaTiO3/Mn0.5Cd0.5S, respectively. By creating an S-scheme heterojunction between CaTiO3 and Mn0.5Cd0.5S, accompanied by a robust internal electric field (IEF), spatial charge separation can be effectively accelerated while ensuring the simultaneous preservation of highly active electrons and holes. Meanwhile, Ni3C nanoparticles, acting as a Schottky-junction H2 generation cocatalyst, can efficiently trap the photoinduced electrons to establish multiple charge transfer channels and supply ample active sites for photoreduction reaction, thereby further optimizing the hydrogen generation kinetics. The integration of a Schottky barrier and S-scheme heterojunction in this research is expected to offer new perspectives for designing other highly effective hybrid catalysts for solar-to-hydrogen fuel conversion.

Superaerophobic Ni3N/Ni@W2N3 multi-heterointerfacial nanoarrays for efficient alkaline electrocatalytic hydrogen evolution reaction

The hydrogen evolution performances of electrocatalysts are greatly restricted by their unfavorable hydrogen evolution kinetics and the undesirable accumulation of as-evolved gas bubbles on the electrocatalysts surface. Herein, we present the fabrication of self-supporting multi-heterointerfacial nanoarrays electrode toward addressing these challenges simultaneously. A monolith Ni3N/Ni@W2N3 electrode is prepared, which exhibits a multi-heterojunction interface between the different components. The construction of this multi-heterojunction interface allows for the redistribution of the electrons, thus alleviating the strong Ni-H bond and optimizing the hydrogen adsorption free energy toward more efficient HER catalysis. Moreover, by virtue of the distinct nanoarray structure, the Ni3N/Ni@W2N3 nanoarrays exhibit improved hydrophilicity and superaerophobicity compared with Ni/Ni3N, facilitating water contact and enabling more efficient detachment of the as-evolved H2 bubbles from the surface. Benefiting from these attractive features, the Ni3N/Ni@W2N3 nanoarrays deliver an attractive alkaline HER catalytic activity with a low overpotential of 66 mV to achieve a current density of 10 mA cm−2, which is comparable with that of the benchmark Pt/C electrode. Moreover, the electrode exhibits remarkable stability during long-term electrolysis. The simultaneous interface and nanostructure engineering provide a feasible pathway for obtaining high-performance electrodes and beyond for various electrochemical reactions.

Tuning the Local Environment of Pt Species at CNT@MO2-x (M = Sn and Ce) Heterointerfaces for Boosted Alkaline Hydrogen Evolution.

As the most promising hydrogen evolution reaction (HER) electrocatalysts, platinum (Pt)-based catalysts still struggle with sluggish kinetics and expensive costs in alkaline media. Herein, we accelerate the alkaline hydrogen evolution kinetics by optimizing the local environment of Pt species and metal oxide heterointerfaces. The well-dispersed PtRu bimetallic clusters with adjacent MO2-x (M = Sn and Ce) on carbon nanotubes (PtRu/CNT@MO2-x) are demonstrated to be a potential electrocatalyst for alkaline HER, exhibiting an overpotential of only 75 mV at 100 mA cm-2 in 1 M KOH. The excellent mass activity of 12.3 mA μg-1Pt+Ru and specific activity of 32.0 mA cm-2ECSA at an overpotential of 70 mV are 56 and 64 times higher than those of commercial Pt/C. Experimental and theoretical investigations reveal that the heterointerfaces between Pt clusters and MO2-x can simultaneously promote H2O adsorption and activation, while the modification with Ru further optimizes H adsorption and H2O dissociation energy barriers. Then, the matching kinetics between the accelerated elementary steps achieved superb hydrogen generation in alkaline media. This work provides new insight into catalytic local environment design to simultaneously optimize the elementary steps for obtaining ideal alkaline HER performance.

Tailoring Mott-Schottky RuO2/MgFe-LDH Heterojunctions in Electrospun Microfibers: A Bifunctional Electrocatalyst for Water Electrolysis.

Hydrogen is a fuel of the future that has the potential to replace conventional fossil fuels in several applications. The quickest and most effective method of producing pure hydrogen with no carbon emissions is water electrolysis. Developing highly active electrocatalysts is crucial due to the slow kinetics of oxygen and hydrogen evolution, which limit the usage of precious metals in water splitting. Interfacial engineering of heterostructures has sparked widespread interest in improving charge transfer efficiency and optimizing adsorption/desorption energetics. The emergence of a built-in-electric field between RuO2 and MgFe-LDH improves the catalytic efficiency toward water splitting reaction. However, LDH-based materials suffer from poor conductivity, necessitating the design of 1D materials by integration of RuO2/ MgFe-LDH to enhance catalytic properties through large surface areas and high electronic conductivity. Experimental results demonstrate lower overpotentials (273 and 122mV at 10mAcm-2) and remarkable stability (60h) for the RuO2/MgFe-LDH/Fiber heterostructure in OER (1m KOH) and HER (0.5m H2SO4) reactions. Density functional theory (DFT) unveils a synergistic mechanism at the RuO2/MgFe-LDH interface, leading to enhanced catalytic activity in OER and improved adsorption energy for hydrogen atoms, thereby facilitating HER catalysis.

Layered deposited MoS2 nanosheets on acorn leaf like CdS as an efficient anti-photocorrosion photocatalyst for hydrogen production

Photocatalytic hydrogen production through water splitting is an appealing technology to alleviate the escalating fossil fuel energy crisis. The advancement of visible-light-driven hydrogen production systems is a crucial aspect of hydrogen research. In this study, we successfully synthesized a unique acorn leaf-like CdS/MoS2 material via a hydrothermal method, with layered deposited MoS2 nanosheets, for driving hydrogen generation under illumination. By systematically varying the sodium molybdate concentration, We looked into how the MoS2 affected the optical properties and photocatalytic performance of the acorn-leaf-like CdS/MoS2.Under illumination, the photocatalytic hydrogen production performance of the acorn leaf-like CdS/MoS2 reached 70.05 mmol·g−1·h−1 (at a catalyst dosage of 10 mg), which is approximately 330 times higher than the unmodified CdS original material. It was determined that the apparent quantum yield at 450 nm was 2.104 %, corresponding to a solar-to-hydrogen conversion efficiency of 9.383 %. Mechanistic investigations revealed that MoS2 nanosheets function as co-catalysts and electron acceptors, effectively promoting electron transfer and the separation of photogenerated charge carriers from CdS, thereby consequently enhancing the kinetics of surface hydrogen evolution. This work offers valuable insights into the development of efficient photocatalysts with anti-photocorrosion properties for sustainable hydrogen production.

Regulating Rh-based rare earth nanoalloy electrocatalysts by scandium, yttrium for accelerated hydrogen evolution kinetics

The construction of rare earth (RE) alloy catalysts offers a route to harness the unique electronic structure of RE. Within the alloy, RE can fine-tune the electronic configuration of the active element, such as rhodium (Rh), via the ligand effect, optimizing the electrochemical reaction pathway. However, the challenging negative reduction potential of RE has impeded the progress in developing RE alloys, particularly nanoalloy catalysts. In this study, Rh3Sc/C and Rh3Y/C nanoalloys were synthesized using a sodium vapor reduction strategy for application as hydrogen evolution reaction (HER) catalysts. Electrochemical tests reveal that Rh-RE alloy catalysts exhibit significantly improved electrocatalytic activity in 1 mol/L KOH. Notably, Rh3Y/C demonstrates exceptional HER performance, achieving a low overpotential of only 31 mV at 10 mA/cm2, surpassing the 50 mV observed for Rh/C. Furthermore, the current density of Rh3Y/C at an 80 mV overpotential is 3.9 times that of Rh/C. This study sheds light on the remarkable catalytic potential of Rh-RE alloys, paving the way for the future expansion of RE nanoalloy systems.

Evaluation of adsorption behaviour of benzylidene chitosan derivatives at mild steel/ 0.5 M H2SO4 solution interface

Four green benzylidene chitosan derivatives (BCs) were synthesized and evaluated as anti-corrosive substances for the first time against mild steel corrosion in 0.5 M H2SO4 solution. The synthesized BCs were laid to infrared spectroscopy and proton resonance spectroscopy for structural confirmation. Gravimetric and electrochemical experiments were accustomed to appraise the effectiveness of inhibitors, however, Scanning Electron Microscopy-Electron Dispersive Spectroscopy (SEM-EDS), Atomic Force Microscopy (AFM), and X-ray Photoelectron Spectroscopy (XPS) were exploited to evaluate the protective mechanism offered by benzylidene chitosan derivatives. Experimental results demarcate the synthesized inhibitors; Anisaldehyde modified Chitosan (CMB), 2-Hydroxy-4-methoxybenzaldehyde modified Chitosan (CHMB), 2,4-Dimethoxybenzaldehyde modified Chitosan (CDMB) and 2-Bromo-4-methoxybenzaldehyde modified Chitosan (CBMB) exhibiting praising inhibitory properties for mild steel corrosion and CDMB was seen possessed preferable inhibition potential at the finest concentration of 500 mgL-1 owing to the proximity of two electron-donating OCH3 groups. Furthermore, the inhibitors have been recorded to behave mixed type with pronounced impact on hydrogen evolution kinetics. The order of inhibition efficacy obtained was CDMB (98.8 %) > CHMB (95.4 %) > CMB (92.8 %) > CBMB (89.2 %) which was further validated by quantum chemical calculations which later opened up about the mechanistic approach involved in electron transfer from inhibitors to metallic vacant orbitals. Additionally, the effect of molecular structure possessed by synthesized inhibitors has been correlated with observed variation in their corrosion inhibition efficiency.

Optimized Transition Metal Phosphides for Direct Seawater Electrolysis: Current Trends.

Seawater electrolysis presents a viable route for sustainable large-scale hydrogen production, yet its practical application is hindered by several technical challenges. These include the sluggish kinetics of hydrogen evolution, poor stability, cation deposition at the cathode, electrode corrosion, and competing chloride oxidation at the anode. To overcome these obstacles, the development of innovative electrocatalysts is crucial. Transition metal phosphides (TMPs) have emerged as promising candidates owing to their superior catalytic performance and tunable structural properties. This review provides a comprehensive analysis of recent progress in the structural engineering of TMPs tailored for efficient seawater electrolysis. We delve into the catalytic mechanisms underpinning hydrogen and oxygen evolution reactions in different pH conditions, along with the detrimental side reactions that impede hydrogen production efficiency. Several methods to prepare TMPs are then introduced. Additionally, detailed discussions on structural modifications and interface engineering tactics are presented, showcasing strategies to enhance the activity and durability of TMP electrocatalysts. By analyzing current research findings, our review aims to inform ongoing research endeavors and foster advancements in seawater electrolysis for practical and ecologically sound hydrogen generation.

VOx-doped CoP catalysts with synergistic dual-active configuration for boosting hydrogen evolution kinetics

Hydrogen evolution reaction (HER), is of great significance to harvest H2 via energy-saving alkaline water electrolysis yet still challenging. Integrating heterogeneous materials is effective in designing favorable electrocatalysts for water dissociation (WD) and H-immediate involved adsorption/desorption behavior and triggering positive interactions to break the kinetics limitation. Herein, a promising configuration of a vanadium-oxide species integrated with cobalt-phosphide plane that grown on the nickel foam (labeled as VOx-CoP/NF), is demonstrated to boost the alkaline HER kinetics comprehensively. The doped vanadium-oxide species preferentially perform the WD process to generate H-intermediates. Meanwhile, interaction between VOx and CoP induce the electronic redistribution that optimizes 3d-2p orbital hybridization state, which balances the adsorption strength of H* to facilitate the hydrogen transfer and enrichment. Eventually, VOx-CoP/NF exhibits supereminent alkaline HER performance with an overpotential of only 65/245 mV at 10/400 mA cm−2, superior to individual CoP and most representative cobalt-phosphide candidates. A flowing anion exchange membrane (AEM) urea-assisted water electrolyzer with VOx-CoP/NF as a bifunctional catalyst, is assembled and achieves a satisfactory performance, verifying its practical feasibility for efficient H2 production. The concept exemplified in this work is that synchronous optimization of elementary reaction step kinetics of HER through reasonable constructing well-defined configuration is instructive for the design of HER electrocatalysts.

Enhancing hydrogen evolution and oxidation kinetics through oxygen insertion into nickel lattice

Nickel-based materials, including metallic Ni and Ni oxide, have been widely studied in the exploration of non-precious-metal hydrogen electrocatalysts, but neither pure Ni nor NiO is ideal for the hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR). In this paper, an oxygen insertion strategy was applied on nickel to regulate its hydrogen electrocatalytic performance, and the oxygen-inserted nickel catalyst was successfully obtained with the assistance of tungsten dioxide support (denoted as O-Ni/WO2). The partial insertion of oxygen in Ni maintains the face-centered cubic arrangement of Ni atoms, simultaneously expanding the lattice and increasing the lattice spacing. Consequently, the adsorption strength of *H and *OH on Ni is optimized, thus resulting in superior electrocatalytic performance of O-Ni/WO2 in alkaline HER/HOR. The Tafel slope of O-Ni/WO2@NF for HER is 56 mV dec−1, and the kinetic current density of O-Ni/WO2 for HOR reaches 4.85 mA cm−2, which is ahead of most currently reported catalysts. Our proposed strategy of inserting an appropriate amount of anions into the metal lattice could provide more possibilities for the design of high-performance catalysts.