Electrocatalytic Process Research Articles

On the Volmer reaction mechanism

Electrochemistry Proton-coupled electron transfer reactions at an electrochemical interface, such as electrosorption of a solvated proton (the Volmer reaction), are the key elementary steps in many electrocatalytic processes. Their characterization is challenging mainly because of the presence of an electric double layer (EDL). Using operando vibrational spectroscopy accompanied by theoretical analysis, Sarkar et al. identified the main stages of the Volmer reaction corresponding to proton discharge from tertiary ammonium with a benzonitrile vibrational tag to a silver electrode surface, and revealed the role of the EDL in this process. They anticipate that their mechanistic insights are general and may be useful in the rational design of materials for electrochemical energy storage and conversion. J. Am. Chem. Soc. 143 , 8381 (2021).

MoS2 Decoration Followed by P Inclusion over Ni-Co Bimetallic Metal-Organic Framework-Derived Heterostructures for Water Splitting.

Demonstrating a highly efficient non-noble bifunctional catalyst for complete water electrolysis remains challenging because of kinetic limitations and crucial importance for future energy harvesting. Herein, a low-cost, integrated composite of a Ni-Co metal-organic framework decorated with thin MoS2 nanosheets was synthesized by a simple hydrothermal method followed by carbonization and phosphorization for electrochemical oxygen and hydrogen evolution reactions. Such a composite heterostructure exhibits outstanding performance in the electrocatalysis process with a lower overpotential of 184 mV for the oxygen evolution reaction (OER) and 84 mV for the hydrogen evolution reaction (HER) in 1.0 M KOH and 0.5 M H2SO4 electrolytes to reach a current density of 10 mA cm-2, with a slight Tafel slope of 63 mV dec-1 for the OER and 96 mV dec-1 for the HER. The obtained results are far better than those of the commercial benchmark catalyst. Furthermore, online gas chromatography quantifies the amount of hydrogen generation in a symmetric cell as equal to 0.002121 moles with an energy efficiency of about 2.237 mg/kWh. Thus, the composite electrode's remarkable performance is further demonstrated as a potentially viable alternative non-noble electrocatalyst for energy conversion reactions.

Cover Feature: Compound‐Specific Imaging of Methanol Fuel Cell for Performance and Degradation Studies Using a Mini Positron Emission Tomograph (Chemistry ‐ Methods 7/2021)

The Cover Feature shows a simple commercial direct methanol fuel cell in a small detector ring Positron Emission Tomography (PET) camera for imaging of the electrocatalytic processes. The PET images present the coverage degree and the distribution of the 11C-labeled methanol with its derivatives along the perforated plate holes of the anode (front) and the cathode (back) sides. The inhomogeneous radioactivity distribution confirms the performance degradation on a certain surface area of the anode catalysts. The presence and extent of the radioactivity on the cathode catalyst layer demonstrates the undesired methanol crossover effect. More information can be found in the Full Paper by Eva Sarkadi-Priboczki et al.

Improved uniformity of Fe3O4 nanoparticles on Fe–N–C nanosheets derived from a 2D covalent organic polymer for oxygen reduction

Developing high-performance non-precious metal-based electrocatalysts for oxygen reduction reaction (ORR) is an urgent demand. In this study, we prepared highly efficient Fe3O4-nanoparticles-decorated Fe–N–C nanosheets (Fe3O4/CCOPHM-F127) from 2D covalent organic polymer (COP) for ORR via a facile impregnation method. The introduced anionic surfactant, i.e. F127, can effectively improve the distribution and size uniformity of Fe3O4 nanoparticles. The onset potential of Fe3O4/COPHM-F127 is 1.0 V, which is equivalent to that of commercial Pt/C. Moreover, the half-wave potential of Fe3O4/COPHM-F127 can reach up to 0.87 V, which is better than that of commercial Pt/C. Fe3O4/COPHM-F127 also exhibits excellent durability and methanol tolerance during the electrocatalytic process.

An Extrinsic Faradaic Layer on CuSn for High-Performance Electrocatalytic CO 2 Reduction

An Extrinsic Faradaic Layer on CuSn for High-Performance Electrocatalytic CO ₂ Reduction

Highly effective degradation of 2,4-Dichlorophenoxyacetic acid herbicide in a three-dimensional sono-electro-Fenton (3D/SEF) system using powder activated carbon (PAC)/Fe3O4 as magnetic particle electrode

The use of chemical pesticides in agriculture to increase the quantity and quality of crops ultimately leads to pollution of water and soil resources. The evaluation of parameters that can affect the efficiency of three-dimensional sono-electro-Fenton (3D/SEF) with PAC/Fe3O4 particle electrodes using and SS316/β-PbO2 anode in 2,4-D degradation, and those parameters were optimized by Taguchi design technique. Different analyses (i.e., Field emission scanning electron microscopy (FESEM), X-ray diffraction analysis (XRD), energy-dispersive X-ray spectroscopy mapping (EDX-mapping), vibrating sample magnetometer (VSM), and Fourier Transform Infrared Spectroscopy (FTIR) could approve the fruitful synthesis of PAC/Fe3O4 and SS316/β-PbO2 anode. By employing LC-MS analysis, the intermediates generated from pollutant degradation were spotted, and degradation pathways was proposed. The pH of the solution (with percentage contribution of up to 39.52%) was as the most effective independent variable on system response. The optimal conditions for removal of 2,4-D were determined to be as follows: 2,4-D concentration = 50 mβL, pH = 3; FeSO4 = 0.08 mg/250 mL, electrolysis time = 60 min, H2O2 concentration = 0.2 mL/L, current density = 5 mA/cm2, catalyst dose = 5 g/L, and Na2SO4 concentration = 0.3 g/250 mL; in these conditions, removal efficiencies of the 2,4-D, COD and TOC were 96.2%, 92.31% and 86.5%, respectively. Moreover, significant reduction was detected in the biological toxicity of the outlet effluent from the 3D/SEF process. Finally, 2,4-D herbicide was completely degraded using hydroxyl radicals produced by the electrocatalytic process and converted into CO2 and H2O products. Considering obtained results, the wastewater containing pesticides such as 2,4-D herbicide can effectively treated by 3D/SEF process, and it could offer acceptable results.

Electronic Structure and d-Band Center Control Engineering over Ni-Doped CoP3 Nanowall Arrays for Boosting Hydrogen Production.

To address the challenge of highly efficient water splitting into H2, successful fabrication of novel porous three-dimensional Ni-doped CoP3 nanowall arrays on carbon cloth was realized, resulting in an effective self-supported electrode for the electrocatalytic hydrogen-evolution reaction. The synthesized samples exhibit rough, curly, and porous structures, which are beneficial for gaseous transfer and diffusion during the electrocatalytic process. As expected, the obtained Ni-doped CoP3 nanowall arrays with a doping concentration of 7% exhibit the promoted electrocatalytic activity. The achieved overpotentials of 176 mV for the hydrogen-evolution reaction afford a current density of 100 mA cm−2, which indicates that electrocatalytic performance can be dramatically enhanced via Ni doping. The Ni-doped CoP3 electrocatalysts with increasing catalytic activity should have significant potential in the field of water splitting into H2. This study also opens an avenue for further enhancement of electrocatalytic performance through tuning of electronic structure and d-band center by doping.

Exceptional Electrochemical HER Performance with Enhanced Electron Transfer between Ru Nanoparticles and Single Atoms Dispersed on a Carbon Substrate

AbstractPrecisely regulating the electronic structures of metal active species is highly desirable for electrocatalysis. However, carbon with inert surface provide weak metal–support interaction, which is insufficient to modulate the electronic structures of metal nanoparticles. Herein, we propose a new method to control the electrocatalytic behavior of supported metal nanoparticles by dispersing single metal atoms on an O‐doped graphene. Ideal atomic metal species are firstly computationally screened. We then verify this concept by deposition of Ru nanoparticles onto an O‐doped graphene decorated with single metal atoms (e.g., Fe, Co, and Ni) for hydrogen evolution reaction (HER). Consistent with theoretical predictions, such hybrid catalysts show outstanding HER performance, much superior to other reported electrocatalysts such as the state‐of‐the‐art Pt/C. This work offers a new strategy for modulating the activity and stability of metal nanoparticles for electrocatalysis processes.

Chemical Vapor Deposition of Hollow Graphitic Spheres for Improved Electrochemical Durability

The wet-chemical synthesis of hollow graphitic spheres, a highly defined model catalyst support for electrocatalytic processes, is laborious and not scalable, which hampers potential applications. Here, we present insights into the chemical vapor deposition (CVD) of ferrocene as a simple, scalable method to synthesize hollow graphitic spheres (HGScvd). During the CVD process, iron and carbon are embedded in the pores of a mesoporous silica template. In a subsequent annealing step, iron facilitates the synthesis of highly ordered graphite structures. We found that the applied temperature treatment allows for controlling of the degree of graphitization and the textural properties of HGScvd. Further, we demonstrate that platinum loaded on HGScvd is significantly more stable during electrochemical degradation protocols than catalysts based on commercial high surface area carbons. The established CVD process allows the scalable synthesis of highly defined HGS and therefore removes one obstacle for a broader application.

Designing C3N-supported single atom catalysts for efficient nitrogen reduction based on descriptor of catalytic activity

The two-step strategy screening based high throughput calculation is an effective method to search for highly active single atom catalysts (SACs) for efficient nitrogen reduction reaction (NRR), sharing a common feature of active metal centers MN4. However, this method faces the lack of descriptor for designing SACs due to limited data. Herein we proposed a robust empirical rule to estimate 312 credible limiting potentials for NRR over 104 C3N-supported SACs. It is found that the limiting potential scales clearly with the adsorption free energies of two key reaction intermediates (∗N2H and ∗NH2), which are significantly dependent on the structure relating descriptor φ, and the activity of SACs with and without N coordination exhibits similar catalytic efficiency. We identified four high-performance SACs having moieties of CrC2N2, CrC4, MnC4 and OsC4 with high selectivity towards NRR and competitive limiting potentials of −0.40, −0.45, −0.53 and −0.54 V, respectively. The φ values for these four SACs are around 19–25 which fall within its optimal ranges of 20–25 validating its prediction fidelity. This work broadens the discovery of two-dimensional carbon-nitrides supported SACs free of N coordination towards efficient N2 reduction and opens a new route of descriptor-guided design of efficient SACs for electrocatalysis process.

Nitrate reduction by electrochemical processes using copper electrode: evaluating operational parameters aiming low nitrite formation.

This work aims to present different electroreduction and electrocatalytic processes configurations to treat nitrate contaminated water. The parameters tested were: current density, cell potential, electrode potential, pH values, cell type and catalyst use. It was found that the nitrite ion is present in all process variations used, being the resulting nitrite concentration higher in an alkaline pH. The increase in current density on galvanostatic operation mode provides a greater reduction of nitrate (64%, 1.4 mA cm-2) if compared to the potentiostatic (20%) and constant cell potential (37%) configurations. In a dual-chamber cell the nitrate reduction with current density of 1.4 mA cm-2 was tested and obtained as a NO3- reduction of 85%. The use of single chamber cell presented 32 ± 3% of nitrate reduction, indicating that in this cell type the nitrate reduction is smaller than in dual-chamber cell (64%). The presence of a Pd catalyst with 3.1% wt. decreased the nitrite (1.0 N-mg L-1) and increased the gaseous compounds (9.4 N-mg L-1) formation. The best configuration showed that, by fixing the current density, the highest nitrate reduction is obtained and the pH presents a significant influence during the tests. The use of the catalyst decreased the nitrite and enhanced the gaseous compounds formation.

Electrocatalytic Water Oxidation by a Trinuclear Copper(II) Complex

Considering the ongoing decrease in the cost of electricity, the development of electrocatalytic processes will gain increasingly more importance in the future. Moreover, with the dwindling of the primary energy source that drives our society, fossil fuels, and the consequences that their utilization has on the environment, it is pivotal to find alternative sustainable energy sources from renewable and carbon free resources. Artificial photosynthesis is a promising strategy for meeting the growing energy demands, where a crucial half-reaction in both natural and artificial photosynthesis is water oxidn. (2H₂O --> O₂ + 4H+ + 4e-), using water as a source of electrons and protons. Inspired by nature, where water oxidn. occurs at the Mn4CaO5 active site of the oxygen evolving complex (OEC) of photosystem II, there has been growing interest in synthetic multinuclear catalysts for promoting intramol. O-O bond formation, with an advantageous redox flexibility for multi-electron transfer arising from the multinuclear core. Here, we employ a mol. trinuclear copper(II) complex, [(DAM)Cu₃(µ³-O)]Cl₄ (DAM = dodecaaza macrotetracycle), as catalyst precursor for electrocatalytic water oxidn. Based on electrochem. studies, we show that this complex is likely an active homogeneous electrocatalyst for water oxidn. in aq. phosphate buffer soln. enabling oxygen evolution with a turnover frequency of approx. 6.0 s⁻¹ at pH =7.

Alkali-induced Transformation of Ni-MOF into Ni(OH)2 Nanostructured Flowers for Efficient Electrocatalytic Methanol Oxidation Reaction.

Post treatment of metal-organic frameworks (MOFs) is widely employed to develop efficient electrocatalysts with better catalytic properties. But the complex processes of post treatment generally led to the collapse of the original structures of MOFs, making the preservation of their pristine hierarchical porous structure a great challenge. Herein, we propose the strategy of alkali treatment of Ni-MOF to transform it into Ni(OH)2 with similar morphology and enhanced electrocatalytic properties for methanol oxidation reaction (MOR). The structure and electrocatalytic properties of as-obtained Ni(OH)2 nanostructured flowers were seriously depended on the alkali concentrations. As the result, Ni(OH)2 obtained from Ni-MOF treated by 0.25 M NaOH (noted as Ni(OH)2 -0.25) performs 1.5 and 2.5 times larger current density than those of Ni(OH)2 -0.025 and Ni(OH)2 -0.5 for MOR. Moreover, the electrocatalytic process and mechanism of MOR on the catalyst of Ni(OH)2 -0.25 are also revealed. Hence, this ex situ conversion strategy of alkali treatment for Ni-MOF uncovered the transformation of MOFs in alkaline solution and develops robust electrocatalyst for practical application of methanol fuel cells.

Electrocatalytic hydrogen evolution: From principle to application

<p indent="0mm">With the increasing global population and increasing energy demands, major concerns have been raised over the security of our energy further. Developing sustainable, fossil-free pathways to produce fuels and chemicals could be an effective strategy. The characteristics of no carbon dioxide emission and high energy density make hydrogen an ideal energy carrier. In the energy conversion process, hydrogen can be generated from renewable energy through the electrocatalytic process and store energy in chemical bonds. It can also be converted back to electronic energy when needed through fuel cells and other equipment. Therefore, exploring efficient hydrogen production methods and conversion pathways is the top priority to realize the application of hydrogen energy. In the hydrogen production strategy, the electrocatalytic pathway has become one of the best solutions for efficient hydrogen production, attributing to its fast, efficient, and high selectivity, and low-cost performance. Since Faraday first defined the concept of electrolyzed water in 1833, different types of electrolytic cell devices appeared in the 1920s and 1930s. A variety of designs for electrocatalytic hydrogen production and coupling reactions have been developed, and great progress has been made in the technology of hydrogen production by electrolysis. This review focuses on the basic principles of electrocatalytic hydrogen production, performance evaluation methods, electrocatalyst types, and electrolyzer structure. Except for the summaries on the latest research progress of electrocatalytic hydrogen production, the existing problems in the current research and possible solutions have also been prospected.

Study on Electrocatalytic Oxidation Technology of Domestic Sewage

Domestic sewage is treated by grapheme-based electrocatalytic oxidation process when adding salt or not. The results show that the removal rate of ammonia nitrogen and COD are 97.86% and 64.29% separately under the conditions of 1g/L salt, 4min residence time and 500A/m2 current density. The COD and ammonia nitrogen of produced water are 72.5mg/L and 1.35mg/L respectively which meet the comprehensive wastewater discharge standard of GB8978–1996, while the removal rate of ammonia nitrogen and COD are 97.22% and 74.55% separately under the conditions of 20 min residence time and 190A/m2 highest current density without adding any salt. The COD and ammonia nitrogen of production water are 57mg/L and 1.7mg/L respectively which meet the comprehensive wastewater discharge standard of GB8978–1996 too. In the experiment, about 95.11 % ~ 97.27 % of ammonia nitrogen is converted into nitrogen. The cleaning effects of the deposition by using hydrochloric acid and citric acid are investigated. The results show that the deposition can be cleaned by both of the 2% hydrochloric acid and 2% citric acid, but the immersion cleaning rate of citric acid which has residual left is slower than hydrochloric acid. The deposition can be thoroughly cleaned by cycle operation.

Mediated Charge Transfer at Nanoelectrodes: A New Approach to Electrochemical Reactivity Mapping and Nanosensing.

Scanning electrochemical microscopy (SECM) is a powerful tool for mapping surface reactivity. Electrochemical mapping of electrocatalytic processes at the nanoscale is, however, challenging because the surface of a nanoelectrode tip is easily fouled by impurities and/or deactivated by products and intermediates of innersphere surface reactions. To overcome this difficulty, we introduce new types of SECM nanotips based on bimolecular electron transfer between the dissolved electroactive species and a redox mediator attached to the surface of a carbon nanoelectrode. A tris(2,2'-bipyridine)ruthenium complex, Ru(bpy)3, that undergoes reversible oxidation/reduction reactions at both positive and negative potentials was used to prepare the SECM nanoprobes for mapping a wide range of electrocatalytic processes through oxidation of H2, reduction of O2, and both oxidation and reduction of H2O2 at the tip. In addition to high-resolution reactivity mapping and localized kinetic measurements, chemically modified nanoelectrodes can serve as nanosensors for a number of important analytes such as reactive oxygen and nitrogen species and neurotransmitters.

Electrocatalytic and Protective Properties of Ruthenium-Derivatized Bacterial Biofilm on Electrodes and Photoelectrodes

Conversion of carbon dioxide is a process of particular scientific interest in recent years, due to the need to reduce the level of this greenhouse gas in the atmosphere by its storage and reduction. Another profit of the CO2 reduction is the possibility of producing useful chemical compounds from such a widespread in the environment source of carbon. Electrochemical and photoelectrochemical reduction of carbon dioxide are optional methods of obtaining fuel materials from CO2. However, because of the molecule stability and by that, high overpotentials of its electroreduction, and moreover because of the competitive hydrogen evolution reaction – efficient and selective catalytic systems active in the CO2 conversion process are sought.There has been proposed a bioelectrocatalytic system for conversion of carbon dioxide, containing bacterial biofilm (of the species Yersinia enterocolitica) at the electrode surface. Biofilms are robust matrices, stable in a wide range of environmental conditions, able to operate at room temperature and under atmospheric pressure, and appear to be attractive for use in electrocatalytic processes. They easily create well developed three-dimensional structures on various types of surfaces, including diverse materials used in the construction of electrodes. Biofilms hydrated matrix allows the electrolyte ions to easily move at the electrocatalytic interface – as a result, biofilms resemble ion-conducting gel-type systems, supporting redox processes. The structure and properties of biofilms make it possible to immobilize catalytically active molecules in the microbial layer grown on the electrode surfaces, and therefore there has been proposed a catalytic system with the organometallic ruthenium (II) complex dispersed in the biological layer, active in the process of carbon dioxide conversion. Ruthenium (II) complex is immobilized in the biofilm matrix by successive modification of the liquid medium (Luria-Bertani medium) for culturing bacteria with a solution of this complex compound. In addition, a biological matrix is used (along with the ruthenium (II) complex molecules dispersed in its layer) as a protective coating, stabilizing the unstable p-type semiconductor – copper (I) oxide. The proposed catalytic system present activity in the photoelectrochemical reduction of carbon dioxide and stability under experimental conditions.

Insight into Direct and Indirect Electrocatalytic Dechlorination of Organic Chlorides By Ultrafine Pd Nanoparticles

Electrocatalytic dehalogenation occurs via both direct and in-direct pathways at the cathode surface playing significant roles in the fields of organic synthesis and environmental remediation. To distinguish these two reduction routes and establish their quantitative relationships in the dehalogenation process are of fundamental interest for unraveling the electrocatalytic dehalogenation mechanisms. However, few studies have been conducted so far. In this work, we prepared ultrafine Pd nanoparticles (NPs) with high dispersibility by simply using N,N-dimethylformamide as solvent and metal-biding agent. The electrochemically active surface area of Pd NPs was 40 m2•g-1, 1.50 times higher than that of commercial Pd/C catalysts. By using the as-prepared Pd NPs as model catalyst, we first showed the direct and indirect reduction of 4-chlorophenol (4-CP) under aqueous conditions in the cyclic voltammogram. The dissociative electron transfer to 4-CP over the Pd NPs electrode was indicated to follow the concerted mechanism. The atomic hydrogen species exclusively existed in the forms of adsorbed hydrogen (H*ads) and absorbed hydrogen (H*abs), which all contributed to the excellent dehalogenation performance. A detailed voltammetric analyses allowed to establish the quantitative relationship between direct and indirect dehalogenation mechanisms, which showed comparable contributions to the electrocatalytic dehalogenation process. This discovery is very important and corrects the previous assertion that the indirect reduction pathway plays a predominant role in the dehalogenation process. This work provides insights into distinguishing the direct and indirect electrocatalytic dehalogenation pathways and successfully bringing the knowledge gap to quantitatively build connection between both dehalogenation routes.

Defective Metal-Organic Frameworks As Unpyrolyzed Electrocatalysts for Oxygen Reduction and Oxygen Evolution Reactions

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) represent core electrocatalytic processes in unitized regenerative fuel cells and rechargeable metal-air batteries catalyzed by the costly platinum group metals (PGMs) materials. Finding highly efficient yet durable ORR/OER catalysts using earth-abundant, low-cost materials represents a critical path in lowering cost barrier for widespread commercialization of the devices. We herein report two approaches to construct defective metal-organic frameworks (MOFs) to remove PGM usage for oxygen electrocatalysis.In approach 1, we prepared a coordinately unsaturated Co-MOF as a bifunctional ORR/OER electrocatalyst in an alkaline electrolyte. The Co-MOF possessed great π-π stacking and hydrogen bonding interactions, giving rise to excellent structural and catalytic stabilities. Structure characterizations demonstrated that the coordination of Co(II) was largely unsaturated. Modeling simulations further confirmed that the unsaturated coordination significantly promoted the interactions with molecular water and oxygen and improved the electronic conductivity, leading to enhanced mass and charge transfer properties.In approach 2, we developed a partial ligand removal (or ligand-defect) approach to create mesopores and unsaturated coordination in a Cu-MOF. Since the micropores typically limit the mass-transfer properties (and the capability to store insoluble discharge product for aprotic metal-air battery), the mesopores of the as-prepared MOF showed less steric hindrance, and the unsaturated Cu coordination also boosted electronic conductivity and auxiliary reactant affinity, leading to high Li-air battery capacity.The defective MOFs may open up a new venue for developing effective electrocatalysts with enhanced intrinsic activity towards oxygen electrocatalysis.

Efficient Electrocatalytic Approach to Spiro[Furo[3,2-b]pyran-2,5′-pyrimidine] Scaffold as Inhibitor of Aldose Reductase

A continuously growing interest in convenient and ‘green’ reaction techniques encourages organic chemists to elaborate on new synthetic methodologies. Nowadays, organic electrochemistry is a new useful method with important synthetic and ecological advantages. The employment of an electrocatalytic methodology in cascade reactions is very promising because it provides the combination of the synthetic virtues of the cascade strategy with the ecological benefits and convenience of electrocatalytic procedures. In this research, a new type of the electrocatalytic cascade transformation was found: the electrochemical cyclization of 1,3-dimethyl-5-[[3-hydroxy-6-(hydroxymethyl)-4-oxo-4H-pyran-2-yl](aryl)methyl]pyrimidine-2,4,6(1H,3H,5H)-triones was carried out in alcohols in an undivided cell in the presence of sodium halides with the selective formation of spiro[furo[3,2-b]pyran-2,5′-pyrimidines] in 59-95% yields. This new electrocatalytic process is a selective, facile, and efficient way to create spiro[furo[3,2-b]pyran-2,5′-pyrimidines], which are pharmacologically active heterocyclic systems with different biomedical applications. Spiro[furo[3,2-b]pyran-2,5′-pyrimidines] were found to occupy the binding pocket of aldose reductase and inhibit it. The values of the binding energy and Lead Finder’s Virtual Screening scoring function showed that the formation of protein–ligand complexes was favorable. The synthesized compounds are promising for the inhibition of aldose reductase. This makes them interesting for study in the treatment of diabetes or similar diseases.