Cathodic Reaction Research Articles

Recent advances in non‐noble metal‐based electrocatalysts for hybrid water electrolysis systems

AbstractThe electrocatalytic water‐splitting process is widely acknowledged as the most sustainable and environmentally friendly technology for hydrogen (H2) production. However, its energy efficiency is significantly constrained by the kinetically slow oxygen evolution reaction (OER) at the anode, which accounts for about 90% of the electrical energy consumption in the water‐splitting process. A new strategy is urgently needed to reduce its energy consumption. In recent years, electrochemical oxidation of small molecules has been considered for replacement of OER for efficient H2 production, due to its benign operational conditions, low theoretical thermodynamic potential, high conversion efficiency and selectivity, and environmental sustainability. Hybrid electrolysis systems, by integrating cathodic hydrogen evolution reaction with anodic oxidation of small molecules, have been introduced, which can generate high‐purity H2 and produce value‐added products or pollutant degradation. In this review, we highlight the recent advancements and significant milestones achieved in hybrid water electrolysis systems. The focus is on non‐noble metal electrocatalysts, reaction mechanisms, and the construction of electrolyzers. Additionally, we present the prevailing challenges and future perspectives pertinent to the evolution of this burgeoning technology.

Machine Learning‐guided Modulation of Li+ Solvation Structures towards Optimal Electrolyte Systems for High‐performance Li‐O2 Battery

As the "blood" of Li‐O2 batteries (LOBs), electrolytes with various solvation structures of Li+ can greatly influence the composition of solid electrolyte interphase (SEI) on anode and the growth kinetics of Li2O2 on cathode, and further the battery performance. However, achieving delicate modulation of the multi‐composition electrolytes remains significantly challenging to simultaneously give consideration to both the anode and cathode reactions. In this work, we employed Bayesian optimization to develop advanced electrolytes for LOBs, enabling the formation of a stable inorganic‐rich SEI, and modulation of Li2O2 morphologies. Thus obtained LOBs using the optimized dual‐solvent electrolyte could deliver a discharge capacity of 14,063 mAh g−1 at a current density of 500 mA g−1, which is far higher than those using the single‐solvent electrolytes. This study not only highlights the critical role of the solvation structure for improving the battery performance, but also provides new insights and important theoretical guidance for delicate modulation of electrolyte compositions.

Machine Learning‐guided Modulation of Li+ Solvation Structures towards Optimal Electrolyte Systems for High‐performance Li‐O2 Battery

As the "blood" of Li‐O2 batteries (LOBs), electrolytes with various solvation structures of Li+ can greatly influence the composition of solid electrolyte interphase (SEI) on anode and the growth kinetics of Li2O2 on cathode, and further the battery performance. However, achieving delicate modulation of the multi‐composition electrolytes remains significantly challenging to simultaneously give consideration to both the anode and cathode reactions. In this work, we employed Bayesian optimization to develop advanced electrolytes for LOBs, enabling the formation of a stable inorganic‐rich SEI, and modulation of Li2O2 morphologies. Thus obtained LOBs using the optimized dual‐solvent electrolyte could deliver a discharge capacity of 14,063 mAh g−1 at a current density of 500 mA g−1, which is far higher than those using the single‐solvent electrolytes. This study not only highlights the critical role of the solvation structure for improving the battery performance, but also provides new insights and important theoretical guidance for delicate modulation of electrolyte compositions.

Electrosynthesis of ethylene glycol from biomass glycerol

Ethylene glycol, a widely used chemical, has a large global capacity exceeding 40 million tons per year. Nevertheless, its production is heavily reliant on fossil fuels, resulting in substantial CO2 emissions. Herein, we report an approach for electrochemically producing ethylene glycol from biomass glycerol. This process involves glycerol electrooxidation to glycolaldehyde at anode, which is subsequently electro-reduced to ethylene glycol at cathode. While the anode reaction has been reported, the cathode reaction remains a challenge. An electrodeposited electrode with metallic Cu catalyst enables us to achieve glycolaldehyde-to-ethylene glycol conversion with an exceptional faradaic efficiency of about 80%. Experimental and theoretical studies reveal that metallic Cu catalyst facilitates the C=O activation, promoting glycolaldehyde hydrogenation into ethylene glycol. We further assemble a zero-gap electrolyzer and demonstrate ethylene glycol electrosynthesis from glycerol to give a decent production rate of 1.32 mmol cm–2 h–1 under a 3.48 V cell voltage. The carbon intensity assessment based on a valid assumption reveals that our strategy may reduce CO2 emissions by over 80 million tons annually compared to conventional fossil fuel routes.

Enhanced Hydrogen Evolution Reaction of a Zn+2-Stabilized Tungstate Electrocatalyst

Due to their diverse properties and functionalities, cost-effective transition metal-based nanomaterials have been rigorously studied for electrochemical applications. Ultrathin nanosheets have been identified as the most effective electrodes for catalyzing water-splitting reactions in both acidic and alkaline environments. Here, we reported ZnWO4, a member of the tungstate family, as an effective electrocatalyst for promoting the electrochemical hydrogen evolution reaction. The Zn+2-stabilized tungstate showed a remarkable cathodic reaction during the water-splitting reaction with low overpotential (136 mV at 10 mA cm−2) and small HER kinetics (Tafel Slope = 75.3 mV dec−1) and long-term cyclic durability. The high-valence tungsten stabilized with divalent Zn+2 promotes electron transfer during the reaction, making it an advanced electrocatalyst for green hydrogen production.

Formulation of thiosemicarbazide based epoxy resin as inhibitor for corrosion of mild steel in 1M HCl: electrochemcial and theoretical studies

ABSTRACT The study presents the development of a new pentafunctional epoxy resin, pentaglycidylthiosemicarbazide (PGTSC), synthesised through a simple condensation process. The molecular structure of PGTSC was characterised using FTIR and 1H NMR spectroscopy. Viscosity measurements indicated that PGTSC's viscosity is significantly influenced by solution concentration and temperature, demonstrating its improved inhibition performance. Electrochemical tests showed that PGTSC achieves a maximum corrosion inhibition efficiency of 92% at a concentration of 10−3 M, with a notable reduction in corrosion current density from 608.60 µA/cm² to 36.67 µA/cm² in 1.0 M HCl. The polarisation studies revealed a mixed-type inhibition mechanism affecting both anodic and cathodic reactions, and the polarisation resistance increased, enhancing the protective properties of steel. The findings were corroborated by additional studies, including PDP, EIS, SEM observations, and computational DFT, MD, and MC calculations support the experimental findings and were in good agreement.

Thermoelectrochemical formation of a solid electrolyte interphase on a silicon negative electrode to enhance the durability of silicon-enriched lithium-ion batteries by compositional modification.

The SiO electrode interface is passivated with a SiO2 layer, which hinders the deposition of an inorganic solid electrolyte interphase (SEI) due to its high surface work function and low exchange current density of electrolyte decomposition. Consequently, a thermally vulnerable, organic-based SEI formed on the SiO electrode, leading to poor cycling performance at elevated temperatures. To address this issue, the SEI formation process is thermoelectrochemically activated. Increasing the formation temperature lowers the work function by shifting the electron energy levels and increases the exchange current density for SEI formation. Higher temperatures promote the incorporation of inorganic Li2CO3 into the SEI film, resulting from the two-electron reduction of ethylene carbonate, and hence the thermally stable SEI film leads to stable cycleability. However, excessively high temperatures cause the SEI layer to become thick and resistive, significantly increasing the polarization of the SiO electrode, which leads to a deficient improvement of cycle performance. Therefore, moderate temperature exposure is required to convert the organic SEI into less resistive, inorganic components. The implementation of a mechanism-assisted SEI formation process in pouch cells using identical materials significantly improves the cycling performance, with a 20% enhancement by the 300th cycle. Additionally, the thermoelectrochemical activation of SEI formation reduces cathodic side reactions on SiO electrodes, which helps in preventing coupled failure of the NCM electrode by mitigating intergranular cracking and preserving its structure.

Enhancing corrosion resistance in HCl environments: Comparative efficacy of a conjugated 3ph-Schiff base versus benzotriazole

This research addresses the need for effective corrosion inhibitors in industrial applications, evaluating the performance of 4-nitro-2-(((1E,2E)-3-phenylallylidene)amino)aniline (noted as 3ph-Schiff base) as a corrosion inhibitor in comparison to benzotriazole (BTA) in a high-concentration 3 M HCl environment. Unlike studies conducted in lower concentrations (e.g. 0.1 and 1 M), this study aims to assess inhibitor performance under more aggressive conditions. Rigorous methods, including Tafel polarisation, electrochemical impedance spectroscopy (EIS), and mass loss measurements, revealed variations in inhibition efficiency (IE). Polarisation data indicated that 3ph-Schiff base at 0.3% (approximately 8.96 mM) achieved a maximum IE of 99.5%, surpassing BTA at the same concentration (approximately 25.2 mM), which recorded an IE of 96.9%. Meanwhile, EIS analysis yielded slightly lower IE values, with 3ph-Schiff base reaching 90.21% and BTA 67.39%, reflecting the complementary nature of these methods. The corrosion inhibition mechanism of 3ph-Schiff base is attributed to strong adsorption on the metal surface, where amino (NH2) and nitro (NO2) groups promote stable complex formation with metal ions, enhancing electron donation and forming a protective layer that blocks corrosive agents. Scanning electron microscopy and elemental mapping confirm uniform nitrogen and carbon surface coverage, integral to the protective layer. This layer acts as both a physical barrier and an electrochemical passivator, effectively reducing anodic and cathodic reactions. The combined effects of adsorption, physical blocking and passivation underscore the 3ph-Schiff base's superior performance as a corrosion inhibitor in acidic environments.

Copper-Doped NiOOH for the Electrocatalytic Conversion of Glycerol to Formate via the Inhibition of the Oxygen Evolution Reaction.

The combination of the electrocatalytic glycerol oxidation reaction (GOR) with the cathodic hydrogen evolution reaction serves to reduce the anodic overpotential, thereby facilitating the efficient production of hydrogen. However, the GOR is confined to a narrow potential range due to the competition of the oxygen evolution reaction (OER) at high potential. Therefore, it is necessary to develop a catalyst with a high Faraday efficiency of formate (FEFA) over a wide potential range. Herein, Cu-doped NiOOH catalysts were synthesized by electrodeposition to inhibit the competing OER during the GOR process, achieving a current density of 10 mA cm-2 at 1.278 V vs RHE, a FEFA over 70.36% within a broad potential range of 1.3 V vs RHE to 1.6 V vs RHE, and a maximum FEFA of 96.46% at 1.35 V vs RHE. In situ spectral studies and DFT calculations revealed that Cu doping slowed the *OH to *O step for the inhibition of the OER and enhanced glycerol adsorption to accelerate the GOR. A competitive reaction mechanism for boosting glycerol electro-oxidation to formate was proposed, presenting a feasible strategy for the highly selective production of electrocatalytic value-added chemicals and the sustainable production of hydrogen energy.

Electrolyte Decoupling Strategy for Metal Oxide-Based Zinc-Ion Batteries Free of Crosstalk Effect.

The crosstalk of transition metal ions between the metal oxide cathode and Zn anode restricts the practical applications of aqueous zinc-ion batteries (ZIBs). Herein, we propose a decoupled electrolyte (DCE) consisting of a nonaqueous-phase (N-phase) anolyte and an aqueous-phase (A-phase) catholyte to prevent the crosstalk of Mn2+, thus extending the lifespan of MnO2-based ZIBs. Experimental measurements and theoretical modelling verify that trimethyl phosphate (TMP) not only synergistically works with NH4Cl in the N-phase anolyte to enable fast Zn2+ conduction while blocking Mn2+ diffusion toward anode, but also modifies the Zn2+ solvation structure to suppress the dendrite formation and corrosion on Zn anode. Meanwhile, the A-phase catholyte effectively accelerates the cathode reaction kinetics. The as-developed Zn|DCE|MnO2 cell delivers 80.13 % capacity retention after 900 cycles at 0.5 A g-1. This approach is applicable for other metal oxide cathode-based ZIBs, thereby opening a new avenue for developing ultrastable ZIBs.

Highly Dispersed Ni-Fe Active Sites on Fullerene based Electron Buffer to boost Oxygen Evolution Reaction

It is critical to develop highly efficient electrocatalysts for water splitting to achieve energy-saving hydrogen production. Recently, fullerene-based electrocatalysts have been widely reported for cathodic hydrogen evolution reaction (HER), while...

Research Progress on Oxygen Reduction Catalyst Materials for Proton Exchange Membrane Fuel Cells

The sustainable development of society gives rise to the increasing energy demand, making environmental pollution a problem that cannot be ignored. Among them, fuel cells are attracting attention as efficient and environmentally friendly. Proton exchange membrane fuel cells (PEMFCs) represent an advanced and eco-friendly energy conversion technology with substantial potential in transportation, distributed power generation, and other applications, while their performance can be remarkably impeded by the cathodic oxygen reduction reaction (ORR) which exhibits slow kinetics. Pt-based catalysts are the preferred materials for catalysis but are detrimental to the practical application of fuel cells due to their high cost and instability. Therefore, it is essential to develop stable and low-cost cathode catalysts. This paper reviews the advancements in cathode catalysts for PEMFCs, encompassing traditional platinum-based catalysts and their enhancement strategies, as well as the current status of emerging non-platinum-based catalysts. The paper also outlines future research directions for these cathode catalysts.

Vanadium-regulated nickel phosphide nanosheets for electrocatalytic sulfion upgrading and hydrogen production.

The electrochemical sulfion oxidation reaction (SOR) is highly desirable to treat sulfion-rich wastewater and achieve energy-saving hydrogen production when coupled with the cathodic hydrogen evolution reaction (HER). Herein, we propose a thermodynamically favorable SOR to couple with the HER, and develop vanadium-doped nickel phosphide (V-Ni2P) nanosheets for simultaneously achieving energy-efficient hydrogen production and sulfur recovery. V doping can efficiently adjust the electronic structure and improve intrinsic activity of Ni2P, which exhibits outstanding electrocatalytic performances for the HER and SOR with low potentials of -0.093 and 0.313 V to afford 10 mA cm-2. Remarkably, the assembled V-Ni2P-based hybrid water electrolyzer coupling the HER with the SOR requires small cell voltages of 0.389 and 0.834 V at 10 and 300 mA cm-2, lower than those required in a traditional water electrolysis system (1.5 and 1.969 V), realizing low-cost sulfion upgrading to value-added sulfur and hydrogen generation. This work provides an approach for energy-saving hydrogen production and toxic waste degradation.

The Electrocatalytic Hydrogen Evolution Performance of Manganese Carbonate in an Acidic Medium

AbstractHydrogen, a sustainable alternative to fossil fuels, can be efficiently produced by electrochemical water splitting, which involves hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode. Both HER and OER require electrocatalysts. The large scale implementation of this technology depends heavily on the development of highly active, stable, and cost‐effective electrocatalysts. In view of this, several electrocatalysts have been explored. Herein, the electrocatalytic hydrogen evolution performance of MnCO3 synthesized by hydrothermal method is reported. While MnCO3 is chosen as the electrocatalyst owing to cost‐effect and abundant precursors, environmental friendliness, and good electrochemical activity, the hydrothermal method is chosen for its simplicity, efficiency, and scalability. The micron size MnCO3 synthesized hydrothermally exhibits η10 of 143 mV, a Tafel slope of 72 mV dec−1 and retains its performance over 3000 cycles and 14 h of continuous operation in 0.5 M H2SO4, demonstrating its utility in sustainable hydrogen production.

Dual-Substitution Strategy Utilizing Cation Chelation and Assembly Process to Realize Solid Solution Reaction in Layered Oxide Cathode for Na-Ion Batteries.

Na0.67Ni0.33Mn0.67O2 (NNM) is regarded as a promising cathode material for Na-ion batteries (NIBs), but suffers from irreversible phase transformations characterized by multiple voltage plateaus, resulting in poor cycle stability and inferior rate capability. To address these issues, the Na0.67Ni0.18Cu0.10Zn0.05Mn0.67O2 (NNCZM) cathode material is synthesized by a cation chelation and reassembly process, which can promote a more uniform element distribution than that prepared by the solid-state method (S-NNCZM), resulting in better Na+ diffusion kinetics and rate capability. Replacing Ni2+ with a small amount of Zn2+ prevents the P2-O2 phase transformation, while replacing Ni2+ with an appropriate amount of electrochemically active Cu2+ eliminates Na-vacancy ordering and additionally contributes to capacity. Thus, the dual substitution of Cu2+ and Zn2+ for Ni2+ makes the NNCZM electrode synergistically achieve a complete solid solution reaction and better cycling stability. Accordingly, it exhibits a large discharge capacity (110.2 mA h g-1 at 10 mA g-1) with a high initial coulombic efficiency (97.3%), remarkable cycle stability with 84.1% capacity retention over 200 cycles at 200 mA g-1, and excellent rate capability with a discharge capacity of 61.0 mA h g-1 at 2000 mA g-1, significantly outperforming the NNM and S-NNCZM electrodes.

Recent Progress on Rechargeable Zn-X (X=S, Se, Te, I2, Br2) Batteries.

Recently, aqueous Zn-X (X=S, Se, Te, I2, Br2) batteries (ZXBs) have attracted extensive attention in large-scale energy storage techniques due to their ultrahigh theoretical capacity and environmental friendliness. To date, despite tremendous research efforts, achieving high energy density in ZXBs remains challenging and requires a synergy of multiple factors including cathode materials, reaction mechanisms, electrodes and electrolytes. In this review, we comprehensively summarize the various reaction conversion mechanism of zinc-sulfur (Zn-S) batteries, zinc-selenium (Zn-Se) batteries, zinc-tellurium (Zn-Te) batteries, zinc-iodine (Zn-I2) batteries, and zinc-bromine (Zn-Br2) batteries, along with recent important progress in the design and electrolyte of advanced cathode (S, Se, Te, I2, Br2) materials. Additionally, we investigate the fundamental questions of ZXBs and highlight the correlation between electrolyte design and battery performance. This review will stimulate an in-deep understanding of ZXBs and guide the design of conversion batteries.

Multistage Generation Mechanisms of Reactive Oxygen Species and Reactive Chlorine Species in a Synergistic System of Anodic Oxidation Coupled with in Situ Free Chlorine and H2O2 Production.

Electro-oxidation (EO) is an efficient approach to removing refractory organics in wastewater. However, the interference from chlorine ions (Cl-) can generate reactive chlorine species (RCS), potentially leading to the production of undesirable chlorinated byproducts. A novel approach involving the cathodic oxygen reduction reaction (ORR) for in situ H2O2 production has emerged as a promising strategy to counteract this issue. This study systematically investigated the dynamics and transformation of RCS and reactive oxygen species (ROS) in an ORR/chloride-containing EO (EO-Cl) system, elucidating their respective roles in organic removal and chlorinated byproduct minimization. Distinct generation rates and patterns were observed for free chlorine and H2O2 in the ORR/EO-Cl system. The rapid generation of free chlorine at the anode quickly reached a dynamic equilibrium, which contrasted with the moderate, continuous cathodic production of H2O2, resulting in considerable H2O2 accumulation over time. This difference established kinetics-driven ROS and RCS formation and distribution, influencing the subsequent organic degradation process. Three distinct stages were identified in the degradation process. In stage I, free chlorine was the primary species, along with reactive species including Cl2•-, 1O2, ClO•, HO•, and Cl•. In stage II, the gradual accumulation of H2O2 consumed free chlorine, favoring the formation of 1O2 and HO•. In stage III, excessive H2O2 quenched the free radicals. Insights into these multistage mechanisms reveal that the rapid degradation of chlorinated byproducts by 1O2 and HO• occurs in stage II of the ORR/EO-Cl system.

Advancing a Comprehensive Model for Carbon Steel Corrosion in Weak Acids: Validation Using Valeric and Acetic Acids

Acidic corrosion in industrial environments represents a serious threat that requires an active prevention and management strategy. In this context, weak acids can create a severe corrosion environment for metallic surfaces, sometimes exceeding the severity observed in strongly acidic solutions under similar conditions. While most of the research efforts of the last decades in the field of the predictive modeling of acidic corrosion have been focused on the specific case of sweet corrosion caused by carbonic acid, the goal of this work is to describe and validate a predictive model to be used as a more transversal tool for acidic corrosion. The model, called the Tafel–Piontelli model, leverages Tafel law to mechanistically describe the electrochemical behavior of carbon steel in acidic aqueous environments. Two different acids, acetic and valeric, were used to experimentally evaluate the performance of the model in weakly acidic solutions, varying the pH and the temperature conditions. Potentiodynamic polarization tests and mass loss tests were performed, allowing us to assess the kinetic parameters (the Tafel slope and the exchange current density of the cathodic and anodic reactions) and corrosion rates of the corrosion process. The promising results suggest that the Tafel–Piontelli model is able to adapt to different scenarios and its intrinsically theoretical nature allows us to extend its predictions outside the range of experimental conditions used to validate it.

Lannea microcarpa Leaves Extract as Corrosion Inhibitor for Aluminium Metal in Acid Medium

Techniques for weight loss, electrochemistry, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) were used to investigate the inhibitory impact of Lannea microcarpa leaves extract. The weight loss data showed that the plant extract's ability to suppress corrosion increased with higher concentrations and decreased with higher temperatures and HCl acid concentrations. According to the electrochemical data, the plant extract uses a mixed type mechanism to limit both cathodic and anodic reaction rates. Calculated activation energies were found to be higher in inhibited systems than in uninhibited systems, indicating physisorption, while negative values of ∆G point to a process that is both possible and spontaneous. The inhibitory mechanism was demonstrated by FTIR spectra to be an adsorption process through the functional groups present in the phytochemicals of the plant extract onto the surface of Al metal. SEM surface morphology study demonstrated the protection that the extract provided on the metal surface. Compared to other isotherm models that were examined, the adsorption data were found to be more reliable and suited the Langmuir isotherm well.

Aminoborate-Catalyzed Reductive Counterreactions for Oxidative Electrosynthetic Transformations.

Electrooxidative transformations frequently rely on proton reduction as the terminal electron sink. However, this cathodic counterreaction can be slow in organic solvents and can operate at reducing potentials that are incompatible with catalysts and reagents needed for oxidative reactions. We report aminoborate adducts as redox mediators for proton reduction that operate at mild reducing potentials. This reliable cathodic couple ultimately enables successful oxidative organic transformations, including chlorodeborylation, developed herein, and Cu-catalyzed Chan-Lam coupling, reported previously by our group. Pyridinium borate adducts formed during electrooxidative chlorination of aryl trifluoroborates serve as easily reduced complexes (-1.1 V vs Fc/Fc+) to catalyze proton reduction. Reactions that promote the formation of borate adducts result in high yields, operate at low cell potentials, suppress aryl trifluoroborate decomposition, and mitigate electrode passivation. These studies illustrate the utility of Lewis acid-base complexes in cathodic counterreactions and underscore the importance of developing both anodic and cathodic reactions in electrosynthesis.