Quantifying intrinsic kinetics of electrochemical reaction controlled by mass transfer of multiple species under rotating disk electrode configuration

Step-by-step guide for electrochemical generation of highly oxidizing reactive species on BDD for beginners

Selecting the ideal anodic potential conditions and corresponding limiting current density to generate reactive oxygen species, especially the hydroxyl radical (•OH), becomes a major challenge when venturing into advanced electrochemical oxidation processes. In this work, a step-by-step guide for the electrochemical generation of •OH on boron-doped diamond (BDD) for beginners is shown, in which the following steps are discussed: i) BDD activation (assuming it is new), ii) the electrochemical response of BDD (in electrolyte and ferri/ferro-cyanide), iii) Tafel plots using sampled current voltammetry to evaluate the overpotential region where •OH is mainly generated, iv) a study of radical entrapment in the overpotential region where •OH generation is predominant according to the Tafel plots, and v) finally, the previously found ideal conditions are applied in the electrochemical degradation of amoxicillin, and the instantaneous current efficiency and relative cost of the process are reported.

PtNi-W/C with Atomically Dispersed Tungsten Sites Toward Boosted ORR in Proton Exchange Membrane Fuel Cell Devices

The performance of proton exchange membrane fuel cells is heavily dependent on the microstructure of electrode catalyst especially at low catalyst loadings. This work shows a hybrid electrocatalyst consisting of PtNi-W alloy nanocrystals loaded on carbon surface with atomically dispersed W sites by a two-step straightforward method. Single-atomic W can be found on the carbon surface, which can form protonic acid sites and establish an extended proton transport network at the catalyst surface. When implemented in membrane electrode assembly as cathode at ultra-low loading of 0.05 mgPt cm-2, the peak power density of the cell is enhanced by 64.4% compared to that with the commercial Pt/C catalyst. The theoretical calculation suggests that the single-atomic W possesses a favorable energetics toward the formation of *OOH whereby the intermediates can be efficiently converted and further reduced to water, revealing a interfacial cascade catalysis facilitated by the single-atomic W. This work highlights a novel functional hybrid electrocatalyst design from the atomic level that enables to solve the bottle-neck issues at device level.

Groundwater arsenic contamination: impacts on human health and agriculture, ex situ treatment techniques and alleviation

Groundwater is consumed by a large number of people as their primary source of drinking water globally. Among all the countries worldwide, nations in South Asia, particularly India and Bangladesh, have severe problem of groundwater arsenic (As) contamination so are on our primary focus in this study. The objective of this review study is to provide a viewpoint about the source of As, the effect of As on human health and agriculture, and available treatment technologies for the removal of As from water. The source of As can be either natural or anthropogenic and exposure mediums can either be air, drinking water, or food. As-polluted groundwater may lead to a reduction in crop yield and quality as As enters the food chain and disrupts it. Chronic As exposure through drinking water is highly associated with the disruption of many internal systems and organs in the human body including cardiovascular, respiratory, nervous, and endocrine systems, soft organs, and skin. We have critically reviewed a complete spectrum of the available ex situ technologies for As removal including oxidation, coagulation-flocculation, adsorption, ion exchange, and membrane process. Along with that, pros and cons of different techniques have also been scrutinized on the basis of past literatures reported. Among all the conventional techniques, coagulation is the most efficient technique, and considering the advanced and emerging techniques, electrocoagulation is the most prominent option to be adopted. At last, we have proposed some mitigation strategies to be followed with few long and short-term ideas which can be adopted to overcome this epidemic.

Identifying diffusion limiting current to unravel the intrinsic kinetics of electrode reactions affected by mass transfer at rotating disk electrode

Rotating disk electrode systems are widely used to study the kinetics of electrocatalytic reactions that may suffer from insufficient mass transfer of the reactants. Kinetic current density at certain overpotential calculated by the Koutecky-Levich equation is commonly used as the metrics to evaluate the activity of electrocatalysts. However, it is frequently found that the diffusion limiting current density is not correctly identified in the literatures. Instead of kinetic current density, the measured current density normalized by diffusion limiting current density ( j/ jL) has also been frequently under circumstance where its validity is not justified. By taking oxygen reduction reaction/hydrogen oxidation reaction/hydrogen evolution reaction as examples, we demonstrate that identifying the actual diffusion limiting current density for the same reaction under otherwise identical conditions from the experimental data is essential to accurately deduce kinetic current density. Our analysis reveals that j/ jL is a rough activity metric which can only be used to qualitatively compare the activity trend under conditions that the mass transfer conditions and the roughness factor of the electrode are exactly the same. In addition, if one wants to use j/ jL to compare the intrinsic activity, the concentration overpotential should be eliminated.

Electrocatalysis in Alkaline Media and Alkaline Membrane-Based Energy Technologies

Hydrogen energy-based electrochemical energy conversion technologies offer the promise of enabling a transition of the global energy landscape from fossil fuels to renewable energy. Here, we present a comprehensive review of the fundamentals of electrocatalysis in alkaline media and applications in alkaline-based energy technologies, particularly alkaline fuel cells and water electrolyzers. Anion exchange (alkaline) membrane fuel cells (AEMFCs) enable the use of nonprecious electrocatalysts for the sluggish oxygen reduction reaction (ORR), relative to proton exchange membrane fuel cells (PEMFCs), which require Pt-based electrocatalysts. However, the hydrogen oxidation reaction (HOR) kinetics is significantly slower in alkaline media than in acidic media. Understanding these phenomena requires applying theoretical and experimental methods to unravel molecular-level thermodynamics and kinetics of hydrogen and oxygen electrocatalysis and, particularly, the proton-coupled electron transfer (PCET) process that takes place in a proton-deficient alkaline media. Extensive electrochemical and spectroscopic studies, on single-crystal Pt and metal oxides, have contributed to the development of activity descriptors, as well as the identification of the nature of active sites, and the rate-determining steps of the HOR and ORR. Among these, the structure and reactivity of interfacial water serve as key potential and pH-dependent kinetic factors that are helping elucidate the origins of the HOR and ORR activity differences in acids and bases. Additionally, deliberately modulating and controlling catalyst-support interactions have provided valuable insights for enhancing catalyst accessibility and durability during operation. The design and synthesis of highly conductive and durable alkaline membranes/ionomers have enabled AEMFCs to reach initial performance metrics equal to or higher than those of PEMFCs. We emphasize the importance of using membrane electrode assemblies (MEAs) to integrate the often separately pursued/optimized electrocatalyst/support and membranes/ionomer components. Operando/in situ methods, at multiscales, and ab initio simulations provide a mechanistic understanding of electron, ion, and mass transport at catalyst/ionomer/membrane interfaces and the necessary guidance to achieve fuel cell operation in air over thousands of hours. We hope that this Review will serve as a roadmap for advancing the scientific understanding of the fundamental factors governing electrochemical energy conversion in alkaline media with the ultimate goal of achieving ultralow Pt or precious-metal-free high-performance and durable alkaline fuel cells and related technologies.

Algehyne E, G. Alshehri M, Bilal M, Khan MA, Muhammad T. The parametric study of hybrid nanofluid flow with heat transition characteristics over a fluctuating spinning disk

The study explored the 3D numerical solution of an unsteady Ag-MgO/water hybrid nanofluid flow with mass and energy transmission generated by a wavy rotating disc moving up and down. The nanofluid is generated in the context of Ag-MgO nanomaterials. Magnesium oxide and silver nanoparticles have been heavily reported to have broad-spectrum antibacterial operations among metal oxides and metals. Silver nanoparticles are without a doubt the most commonly used inorganic nanoparticles, with numerous innovations in biomaterial’s detection and antimicrobial operations. However, in current paper, the intention of the analysis is to boost thermal energy transmitting rates for a range of industrial implementations. When compared to a flat surface, energy transition is increased up to 15% due to the wavy swirling surface. The problem has been formulated as a system of PDEs, which included the Navier Stokes and Maxwell equations. Following that, the modeled equations are reduced to a dimensionless system of differential equations. The derived equations are then solved numerically using the Parametric Continuation Method (PCM). The findings are displayed graphically and debated. The geometry of a spinning disc is thought to have a positive impact on velocity and heat energy transfer. The insertion of nanostructured materials (silver and magnesium-oxide) increased the carrier fluid’s thermal properties considerably. It is more effective at dealing with low energy transmission.

How Buffers Resist Electrochemical Reaction-Induced pH Shift under a Rotating Disk Electrode Configuration

In mild acidic or alkaline solutions with limited buffer capacity, the pH at the electrode/electrolyte interface (pH^s) may change significantly when the supply of H⁺ (or OH^-) is slower than its consumption or production by the electrode reaction. Buffer pairs are usually applied to resist the change of pH^s during the electrochemical reaction. In this work, by taking H₂X ⇄ 2H⁺ + X + 2e^- under a rotating disk electrode configuration as a model reaction, numerical simulations are carried out to figure out how pH^s changes with the reaction rate in solutions of different bulk pHs (pH^b in the range from 0 to 14) and in the presence of buffer pairs with different pK_a values and concentrations. The quantitative relation of pH^s, pH^b, pK_a, and concentration of buffer pairs as well as of the reaction current density is established. Diagrams of pH^s and ΔpH (ΔpH = pH^s - pH^b) as a function of pH^b and the reaction current density as well as of the j_max-pH^b plots are provided, where j_max is defined as the maximum allowable current density within the acceptable tolerance of deviation of pH^s from that of pH^b (e.g., ΔpH < 0.2). The j-pH^s diagrams allow one to estimate the pH^s and ΔpH without direct measurement. The j_max-pH^b plots may serve as a guideline for choosing buffer pairs with appropriate pK_a and concentration to mitigate the pH^s shift induced by electrode reactions.

How to Improve the Performance of Electrochemical Sensors via Minimization of Electrode Passivation

It follows from critical evaluation of possibilities and limitations of modern voltammetric/amperometric methods that one of the biggest obstacles in their practical applications in real sample analysis is connected with electrode passivation/fouling by electrode reaction products and/or matrix components. This review summarizes possibilities how to minimise these problems in the field of detection of small organic molecules and critically compares their potential and acceptability in practical laboratories. Attention is focused on simple and fast electrode surface renewal, the use of disposable electrodes just for one and/or few measurements, surface modification minimising electrode fouling, measuring in flowing systems, application of rotating disc electrode, the use of novel separation methods preventing access of passivating particles to electrode surface and the novel electrode materials more resistant toward passivation. An attempt is made to predict further development in this field and to stress the need for more systematic and less random research resulting in new measuring protocols less amenable to complications connected with electrode passivation.