Electrocatalytic Water Oxidation: An Overview With an Example of Translation From Lab to Market

Electrocatalytic Poly(3,4-ethylenedioxythiophene) for Electrochemical Conversion of 5-Hydroxymethylfurfural

This study investigates the utilization of the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) as a catalytic material for the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). PEDOT films doped with different counterions were electrodeposited on graphite foil. In particular, the mobile anion perchlorate and the polymeric ionomers polystyrenesulfonate, Nafion, and Aquivion were used. The electrocatalytic properties of PEDOT films were evaluated toward the TEMPO redox mediator in the absence and the presence of HMF as a substrate for oxidation reactions. The electrocatalytic HMF oxidation was confirmed to occur at PEDOT electrodes, and it was also found that the chemical nature of PEDOT counterions controls the electrocatalytic conversion of HMF by modulating the kinetics of the electrochemical generation of the oxoammonium cation TEMPO(+). Potentiostatic electrolysis experiments showed that both the reference graphite electrode and PEDOT substrates were able to convert HMF to FDCA with an 80% faradaic efficiency (FE) and a >90% yield (FDCA), but, compared to graphite, the complete conversion of HMF to FDCA required a ca. 30% shorter time when using PEDOT electrodes doped with perchlorate or Aquivion, thanks to their ability to sustain a higher current density in the initial phase of the electrolysis. In addition, while all PEDOT films were chemically stable under the electrochemical conditions herein described, only PEDOT films doped with Aquivion were also mechanically robust and stable against delamination. Thus, the new PEDOT/Aquivion composite may represent the best choice for the implementation of PEDOT-based electrodes in TEMPO-mediated electrocatalytic applications.

Electrochemical hydrogenation and oxidation of organic species involving water

Fossil fuel-driven thermochemical hydrogenation and oxidation using high-pressure H2 and O2 are still popular but energy-intensive CO2-emitting processes. At present, developing renewable energy-powered electrochemical technologies, especially those using clean, safe and easy-to-handle reducing agents and oxidants for organic hydrogenation and oxidation reactions, is urgently needed. Water is an ideal carrier of hydrogen and oxygen. Electrochemistry provides a powerful route to drive water splitting under ambient conditions. Thus, electrochemical hydrogenation and oxidation transformations involving water as the hydrogen source and oxidant, respectively, have been developed to be mild and efficient tools to synthesize organic hydrogenated and oxidized products. In this Review, we highlight the advances in water-participating electrochemical hydrogenation and oxidation reactions of representative organic molecules. Typical electrode materials, performance metrics and key characterization techniques are firstly introduced. General electrocatalyst design principles and controlling the microenvironment for promoting hydrogenation and oxygenation reactions involving water are summarized. Furthermore, paired hydrogenation and oxidation reactions are briefly introduced before finally discussing the challenges and future opportunities of this research field.

Electron Spin Selective Iridium Electrocatalysts for the Oxygen Evolution Reaction

Highly efficient electrocatalysts for water electrolysis are crucial to the widespread commercialization of the technology and an important step forward toward a sustainable energy future. In this study, an alternative method for boosting the electrocatalytic activity toward the oxygen evolution reaction (OER) of a well-known electrocatalyst (iridium) is presented. Iridium nanoparticles (2.1 ± 0.2 nm in diameter) functionalized with chiral molecules were found to markedly enhance the activity of the OER when compared to unfunctionalized and achiral functionalized iridium nanoparticles. At a potential of 1.55 V vs Reference Hydrogen Electrode (RHE), chiral functionalized iridium nanoparticles exhibited an average 85% enhancement in activity with respect to unfunctionalized iridium nanoparticles compared to an average 13% enhancement for the achiral functionalized iridium nanoparticle. This activity enhancement is attributed to a spin-selective electron transfer mechanism taking place on the chiral functionalized catalysts, a characteristic induced by the chirality of the ligand. This alternative path for the OER drastically reduces the production of hydrogen peroxide, which was confirmed via a colorimetric method.

A new approach for cobalt (II) removal from simulated wastewater using electro membrane extraction with a flat sheet supported liquid membrane

The aim of this work was to efficiently remove cobalt (Co) from aqueous solutions by using a novel Electromembrane Extraction (EME) technique. This novel electrochemical cell design featured two distinct glass chambers, incorporating a Supported Liquid Membrane (SLM) composed of a polypropylene flat membrane saturated with 1-octanol and a carrier substance, as well as electrodes constructed from graphite and stainless steel. The investigation covered an exploration of various effective parameters like, carrier type, voltage across the cell, donor solution pH, and the initial Co concentration, with the overarching goal of comprehending their individual effect on Co removal efficiency. Notably, two different carriers, tris(2-ethylhexyl) phosphate (TEHP) and bis(2-ethylhexyl) phosphate (DEHP), were systematically evaluated in combination with 1-octanol. The findings underscored the pivotal role of the cell voltage in significantly enhancing the mass transfer rate of cobalt across the membrane, thereby advancing the effectiveness of the removal process. After a comprehensive optimization process, the optimal operating conditions were established as follows: employing 1-octanol with 1.0 % v/v bis(2-ethylhexyl) phosphate as a carrier, applying a voltage of 60 V, maintaining an initial pH of 5, utilizing an initial cobalt concentration of 15 mg/L, conducting an extraction for 6 h, and employing a stirring rate of 1000 rpm. Remarkably, these conditions led to the attainment of an impressive removal efficiency of 87 %. In stark contrast, when no voltage was applied, the removal efficiency did not surpass 40 %. This underscores the pivotal role of the applied voltage in enhancing the cobalt removal process under the specified conditions.

On the Temperature Sensitivity of Electrochemical Reaction Thermodynamics

Herein, we report a method to estimate the thermodynamic potentials of electrochemical reactions at different temperatures. We use a two-term Taylor series approximation of thermodynamic potential as a function of temperature, and we calculate the temperature sensitivity for a family of twenty seven known half reactions. We further analyze pairs of cathode and anode half-cells to pinpoint optimal voltage matches and discuss implications of changes in temperature on overall cell voltages. Using these observations, we look forward to increased interest in temperature and idealized half-reaction pairing as experimental choices for the optimization of electrochemical processes.

Dealloying fabrication of hierarchical porous Nickel–Iron foams for efficient oxygen evolution reaction

Designing and preparing highly active oxygen evolution reaction (OER) electrodes are essential for improving the overall efficiency of water splitting. Increasing the number of active sites is the simplest way to enhance OER performance. Herein, we present a dealloy-etched Ni–Fe foam with a hierarchical nanoporous structure as integrated electrodes with excellent performance for OER. Using the dealloying method on the Ni–Fe foam framework, a nanoporous structure is produced, which is named nanoporous Ni–Fe@Ni–Fe foam (NP-NF@NFF). Because of the peculiarities of the dealloying method, the NP-NF@NFF produced contains oxygen vacancies and heterojunctions. As a result, NP-NF@NFF electrode outperforms state-of-the-art noble metal catalysts with an extremely low overpotential of 210 and 285 mV at current densities of 10 and 100 mA cm−2, respectively. Additionally, the NP-NF@NFF electrode shows a 60-h stability period. Therefore, NP-NF@NFF provides new insights into the investigation of high-performance transition metal foam electrodes with effective active sites for efficient oxygen evolution at high current densities.