Electrochemical Oxidation Reaction Research Articles

Selective Electrocatalytic Oxidation of Nitrogen to Nitric Acid Using Manganese Phthalocyanine.

Ammonia is produced through the energy-intensive Haber-Bosch process, which undergoes catalytic oxidation for the production of commercial nitric acid by the senescent Ostwald process. The two energy-intensive industrial processes demand for process sustainability. Hence, single-step electrocatalysis offers a promising approach toward a more environmentally friendly solution. Herein, we report a 10-electron pathway associated one-step electrochemical dinitrogen oxidation reaction (N2OR) to nitric acid by manganese phthalocyanine (MnPc) hollow nano-structures under ambient conditions. The catalyst delivers a nitric acid yield of 513.2 μmol h-1 gcat-1 with 33.9% Faradaic efficiency @ 2.1 V versus reversible hydrogen electrode. The excellent N2OR performances are achieved due to the specific-selectivity, presence of greater number of exposed active sites, recyclability, and long period stability. The extended X-ray absorption fine structure confirms that Mn atoms are coordinated to the pyrrolic and pyridinic nitrogen via Mn-N4 coordination. Density functional theory-based theoretical calculations confirm that the Mn-N4 site of MnPc is the main active center for N2OR, which suppresses the oxygen evolution reaction. This work provides a new arena about the successful example of one step nitric acid production utilizing a Mn-N4 active site-based metal phthalocyanine electrocatalyst by dinitrogen oxidation for the development of a carbon-neutral sustainable society.

Atomically embedded synergetic dual-metal catalysis FeO&MoS2 nanoparticles on sodalite structural zeolite toward electrochemical methanol oxidation reaction

To improve the performance of the direct methanol fuel cells (DMFCs), the atomically embedded synergetic dual-metal catalyst nanosized ferrous oxide & molybdenum disulfide @ sodalite structural zeolite (FeO&MoS2@SOD) is designed and generated through self-assemble process under hydrothermal condition. The FeO&MoS2@SOD is characterized by SEM, XRD, TEM, EDX and XPS to reveal its morphology, composition, fine structure, element distribution and element valence, respectively. Its performance in the electrochemical methanol oxidation reaction (MOR) is investigated by EIS, CV and A i-t C with the current density of 24.33 mA cm−2 or 144 mA mg−1, and the power density of 33.99 mW cm−2. The excellent behavior of the obtained catalyst could be ascribed to the synergic effect of the highly dispersed FeO and MoS2 nanoparticles on the surface of the zeolite.

Oxygen-deficient WO3-x spheres for electrochemical N2 oxidation to nitrate

Nitrate synthesis via the electrochemical nitrogen oxidation reaction (e-NOR) is widely recognized as a potential alternative to the energy-intensive Ostwald process. However, electrocatalysts with strong N2 adsorption and activation abilities remain largely undeveloped due to kinetic hindrances caused by the high bond energy of NN. Here we designed a hollow WO3 sphere with an optimal concentration of oxygen vacancies and studied its e-NOR performance. The optimally synthesized oxygen-deficient WO3 (WO3-x) achieved a high nitrate yield of 311.15 µmol h−1gcat.-1 and a Faraday efficiency of 2.00 %, which is probably due to the presence of a moderate amount of oxygen vacancies on the WO3-x surface and the hollow spherical structure, which further improves the accessibility of the inner active surface. Our work could potentially stimulate research into transition metal oxide-based materials for e-NOR applications.

Metal-organic frameworks-derived oxalate ligand modified NiCo hydroxides for enhanced electrochemical glycerol oxidation reaction

Glycerol oxidation reaction can be substituted for oxygen evolution reaction for more efficient hydrogen production due to its lower thermodynamic potential. Herein, a series of NiCo hydroxide nanosheets containing abundant Ni3+ species and surface ligands were synthesized by in-situ structural transformation of bimetallic organic frameworks in alkaline media for efficient glycerol oxidation reaction. It is found that the incorporation of Co ions increases the content of the Ni3+ species, and that the Ni/Co ratio of 1.0 lead to the optimal catalytic performance. The oxalate-modified nickel–cobalt hydroxide with the optimized Ni/Co ratio can deliver a current density of 10 mA cm−2 at 1.26 V vs. RHE (reversible hydrogen electrode), and reaches its maximum selectivity and Faradaic efficiency at 1.30 V vs. RHE. A high selectivity of 82.9% and a Faradaic efficiency of 91.0% are achieved. The high catalytic activity can be mainly attributed to the abundant Ni3+ species and surface carboxyl groups.

Urea Electrooxidation in Alkaline Environment: Fundamentals and Applications

AbstractInvited for this issue's Front Cover is the group of Dr. Shun Lu of Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences (China). The cover picture shows the electrochemical urea oxidation reaction has been a key reaction among urea‐assisted hydrogen production, direct urea fuel cell, urea‐containing wastewater urea removal and urea sensors. Read the full text of the Concept at 10.1002/celc.202300138.

Nickel–Cobalt Selenide Electrocatalytic Electrode toward Glucose Oxidation Coupling with Alkaline Hydrogen Production

Electrochemical glucose oxidation reaction (GOR) is a promising alternative anodic reaction to water oxidation reaction for various electrochemical oxidation reactions owing to the relatively low thermodynamic potential of GOR and the abundant source of glucose from biomass-based platform molecules. However, it remains difficult to develop high-activity and low-cost electrocatalysts toward GOR. Herein, we report a NiCoSex nanoplate supported on Ni foam with excellent activity for GOR electrocatalysis, which achieves a high current density of 500 mA cm-2 at 1.41 V vs reversible hydrogen electrode (RHE) and a 70.2% Faraday efficiency of formate at 1.40 V vs RHE. The surface component evolution of NiCoSex is studied by an in situ Raman spectrum, which points out the catalytic active species to be CoOx/CoOOH and NiOOH. Furthermore, we develop a two-electrode cell by pairing GOR with hydrogen evolution reaction using the NiCoSex electrode as the bifunctional catalyst for the anode and the cathode, which only requires an applied voltage of 1.50 V to reach a high current density of 200 mA cm-2 and retains long-term stability over 18 h with a high Faraday efficiency of H2 (close to 100%) in the cathode.

Heterojunction Engineering for Electrocatalytic Applications

Production of green hydrogen from the electrolysis of water is considered to be one of the most desirable processes to address the clean energy demand. However, a high energy barrier and an economically unsustainable nature limit the process toward practical implementation in an extensive way. The designing of an electrocatalyst accompanied by defect engineering, heteroatom doping, and strain creation are known to be effective strategies to make the process efficient. Recently, construction of heterojunctions with a combination of materials with desired band structures is considered to be a smart approach in promoting electrocatalytic activities by attaining charge redistribution and manipulating the electronic structure at the interface. The present review elaborately discusses possible heterojunctions, alterations at the interface, insight thermodynamics, and possible causes for boosting electrocatalytic activities. The heterojunction-based electrocatalysts are found not only effective for oxygen evolution reactions and hydrogen evolution reactions, but also to be very useful toward various electrochemical oxidation reactions as well as electrochemical reduction reactions involving small molecules undergoing decomposition at very low energy. Having such a specialty, there is no doubt that heterojunction-based electrocatalysts are going to be the primary choices of researchers in coming years.

The identification of dual active routes for highly efficient furfural oxidation reaction coupling with hydrogen production over Re modulated Co(OH)2/CC

It is of great significance and challenge to tune the active sites of two-dimensional materials and identify the exclusive active sites for separate reaction toward hydrogen evolution reaction (HER) coupled with electrochemical oxidation (ECO) reaction. Herein, Re was introduced to tune d band charge density of Co, which reduced the energy barrier of water splitting for HER. Meanwhile, the abundant oxygen vacancies (Ov) caused by Re introduction resulted in a new reaction route for furfural oxidation reaction (FOR). That is, the adsorbed OH− on Ov accelerates the dehydrogenation of Co(OH)O, and the active site further promotes the nucleophile dehydrogenation, thus improving the catalytic performance of FOR. In conclusion, Re-Co(OH)2/CC with Re modified Co-centered sites displays dual active routes, which simultaneously enhance FOR and HER with a cell voltage (1.36 V) at 10 mA cm−2, surpassing the most two-dimensional transition-metal hydroxides (2D TMHs) results reported as we known. This work provides new insights into the modulation of Co electronic structure and Ov concentration, which results in enhanced bifunctional electrocatalytic reactions.

Tuning selectivity and activity of the electrochemical glycerol oxidation reaction by manipulating morphology and exposed facet of spinel cobalt oxides

To further explore the electrooxidation mechanism of biomass-based compounds, it is highly desirable to regulate the proportion of reactive facets and identify facet-governing reactivity through crystal facet engineering. In this study, octahedral and cubic cobalt spinel oxide (Co3O4), each exclusively exposed by one specific type of facet, are selected as two representative microstructure models for tuning the selectivity and productivity of electrochemical glycerol oxidation reaction. The results indicate that the {111}-dominant octahedral Co3O4 plane with a higher population of Co2+ sites exhibits superior electrocatalytic activity for glycerol oxidation compared with the {001}-dominant cubic Co3O4, allowing nearly 65% of glycerol to be converted into a high-value-added dihydroxyacetone (DHA) compound. The average DHA production rate over octahedral Co3O4 (2.5 μmol cm−2h−1) are approximately 3.5 times greater than that over cubic Co3O4 (0.7 μmol cm−2h−1). Electrochemical studies and surface atomic configuration analysis reveal that {111}-dominant octahedral Co3O4 with a higher density of active cobalt ion yields unique reactant adsorption and charge transfer, leading to increased glycerol oxidation reactivity and productivity. The present study emphasizes the significance of controlling the highly active facet in developing efficient and selective electrocatalysts.

Urea Electrooxidation in Alkaline Environment: Fundamentals and Applications

AbstractUrea is an important chemical in agricultural, biosystem and chemical engineering. It can not only be a fertilizer and feed supplement, but also converted into electricity and hydrogen based on the counterpart half‐reactions. In this concept, we demonstrated the fundamental mechanism of electrochemical urea oxidation reaction (UOR) and its various applications on environmental, energy and healthcare devices with typical examples. UOR providing potential directions for the electrochemical treatment of urea‐contained wastewater were also introduced in this concept. This work is not focused on electrocatalyst design, but rather offers instructive guidance for the UOR developments in environmental, energy, and healthcare devices.

Self-supporting CuM LDH (M = Ni, Fe, Co) carbon cloth electrodes for selective electrochemical ammonia oxidation to nitrogen

Electrochemical ammonia oxidation reaction (eAOR) has important applications in ammonia fuel cells and wastewater treatment due to its environmental friendliness and convenient operation. In this study, hydrothermal synthesis was used to create self-supported CuM (M = Ni, Fe, Co) carbon cloth electrodes. After three hours of electrolysis at 1.65 V vs. RHE, a CuCo/CC electrode with the ideal Cu/Co ratio (1:2) achieved the maximum dinitrogen selectivity of 90.0% and Faraday efficiency of 77.4%. The reaction mechanism was investigated using Raman and in-situ IR spectroscopy. Cu serves as NH3 adsorption sites and Co catalyzes the oxidation, and together achieve high efficiency.

Revealing and Optimizing the Dialectical Relationship Between NOR and OER: Cation Vacancy Engineering Enables RuO2 With Unanticipated High Electrochemical Nitrogen Oxidation Performance

AbstractThe electrochemical N2 oxidation reaction (NOR) using water and atmospheric N2 represents a sustainable approach to nitric acid production; while, the parasitic oxygen evolution reaction (OER) usually results in poor conversion selectivity of N2 oxidation. Although the side‐reaction can be partially suppressed by using OER‐inactive catalysts or substrates, the optimized performance is usually obtained at the cost of low yield. Revealing the internal relationship between NOR and OER, providing an effective pathway to optimize the dialectical relationship between OER and NOR is desirable and of socio‐economic significance. Herein, RuO2, the well‐known OER electrocatalyst, is defectively engineered to enhance the cooperation rather than competition between NOR and OER; a Faradaic efficiency (FE) of 6.70% at 1.36 V and a maximum yield of 767.92 µg h−1 mgcat−1 at 1.44 V are obtained on D‐RuO2 in acid electrolyte, superior to all the previously reported works. Experiments and DFT calculations suggest that the OER intermediates play a crucial role and the real rate‐determining step during nitrogen oxidation is the transition from *O to *OOH involved in the formation of *NN(OH). The outstanding NOR activity is ascribed to the enhanced stabilization of *OH and the promotion of OO bond breakage in the rate determining step of *NN(OH) formation.

Unveiling the role of hydroxyl groups in glycerol as a critical descriptor for efficient electrocatalytic reforming of biomass molecules using PtCu alloy nanoparticle catalysts

Glycerol, one of the main byproducts of biodiesel production, has recently attracted attention since it can co-generate electricity and valuable chemicals via electrochemical glycerol oxidation reaction (EGOR). Due to the complexity of EGOR, there have been many arguments about its pathways to find the environmental conditions for producing targeted chemicals. The studies to find the representative descriptor that affects EGOR were performed, using a combination of ab-initio computational and experimental approaches. A novel porous carbon (PC) was employed as an effective support material to synthesize PtCu/PC catalysts, and then various electrochemical analyses were carried out. The adsorption energies of hydroxide and the binding strength of the hydroxyl groups in the glycerol on the catalysts were compared using a crystal orbital Hamilton population (COHP) analysis. Consequently, we found the tendency in the binding strength of hydroxyl group as a critical descriptor, rationalizing why the PtCu3/PC catalyst revealed the highest mass activity for EGOR.

Understanding Trends in Electrochemical Methanol Oxidation Reaction Activity on a Single Transition-Metal Atom Embedded in N-Coordinated Graphene Catalysts

The lack of efficient catalysts and research on the mechanism for the methanol oxidation reaction (MOR) impedes the development of direct methanol fuel cells. In this work, based on density functional theory calculations, we systematically investigated the activity trends of electrochemical MOR on a single transition-metal atom embedded in N-coordinated graphene (M@N4C). By calculating the free energy diagrams of MOR on M@N4C, Co@N4C was screened out to be the most effective MOR catalyst with a low limiting potential of 0.41 V due to the unique charge transfers and electronic structures. Importantly, one- and two-dimensional volcano relationships in MOR on M@N4C catalysts are established based on the d-band center and the Gibbs free energy of and ΔG*CO, respectively. In one word, this work provides theoretical guides toward the improved activity of MOR on M@N4C and hints for the design of active and efficient MOR electrocatalysts.

Directed Urea‐to‐Nitrite Electrooxidation via Tuning Intermediate Adsorption on Co, Ge Co‐Doped Ni Sites

AbstractThe electrochemical urea oxidation reaction (UOR) is an alternative to electrooxidation of water for energy–saving hydrogen (H2) production. To maximize this purpose, design of catalysts for selective urea‐to‐nitrite (NO2–) electrooxidation with increased electron transfer and high current is practically important. Herein, a cobalt, germanium (Co, Ge) co‐doped nickel (Ni) oxyhydroxide catalyst is reported first time that directs urea‐to‐NO2– conversion with a significant Faradaic efficiency of 84.9% at 1.4 V versus reversible hydrogen electrode and significantly boosts UOR activity to 448.0 mA cm−2. Importantly, this performance is greater than for most reported Ni‐based catalysts. Based on judiciously combined synchrotron‐based measurement, in situ spectroscopy and density functional theoretical computation, significantly boosted urea‐to‐NO2– production results from Co, Ge co‐doping is demonstrated that optimizes electronic structure of Ni sites in which urea adsorption is altered as NO‐terminal configuration to facilitate CN cleavage for *NH formation, and thereby expedites pathway for urea to NO2– conversion. Findings highlight the importance of tuning intermediate adsorption behavior for design of high‐performance UOR electrocatalysts, and will be of practical benefit to a range of researchers and manufacturers in replacing conventional water electrooxidation with UOR for energy‐saving H2 production.

Influence of bubble generation on the microchannel electrochemical gas evolution reaction

To understand the influence of bubble generation on electrochemical reaction in microchannel reactor, visualized experimental research was carried out to analyze the bubble growth and detachment behaviors on needle electrode and investigate the voltage–time diagrams of a typical electrochemical oxidation and hydrogen evolution reaction. Two kinds of gas–liquid flow patterns were observed in the microchannel reactor, which caused different current fluctuations in the linear sweep voltammetry experiment. Quickly bubble rupturing was important for maintaining stable electrochemical reaction by avoiding the block of ionic conduction between electrodes. The voltage fluctuation caused by periodic growth and detachment of bubble on the needle electrode clearly exhibited the variation of electrochemical reaction process. The diameter of the bubble shear-ruptured from the electrode was exponential with the capillary number of electrolyte solution, and the relative diameter of bubble and electrode was linear with the relative voltage fluctuation. The voltage fluctuation was mainly contributed by the bubble induced activation and ohmic overpotentials, which ratios were almost 50% respectively.

Tailored Bimetallic Ni-Sn Catalyst for Electrochemical Ammonia Oxidation to Dinitrogen with High Selectivity.

Direct electrochemical ammonia oxidation reaction (eAOR) is an efficient and sustainable strategy to process wastewater containing ammonia, and it endures overoxidation and severely competitive oxygen evolution reaction (OER). Herein, we synthesized a Ni(OH)2/SnO2 composite catalyst by a multistep strategy and applied it to the eAOR process. Ni(OH)2/SnO2 exhibited a N2-N Faradaic efficiency (FEN2-N) of 84.2%, with a N2 partial current density (jN2-N) of 2.7 mA cm-2 at 1.55 V vs reversible hydrogen electrode (RHE) in 0.5 M K2SO4 with 10 mM NH3-N (pH 11). The oxophilic Sn promoted NH3 absorption on Ni sites while suppressing the OER. As the active species, NiOOH accelerated the dimerization of intermediates (*NH2 or *NH) to form N2.

Evaluation of Pd-Co Bimetallic Electrocatalysts in the Formic Acid Oxidation Reaction

The main focus of this research is the synthesis and evaluation of Pd-Co bimetallic catalysts, in the formic acid electrochemical oxidation reaction (FAOR). The catalysts used were synthesized by electrodeposition using a choline chloride and urea Deep Eutectic Solvent (DES) termed reline, as electrolytic medium. Electrodeposition potentials were previously selected after analysis by Cyclic Voltammetry (CV) and used in Chronoamperometry (CA). The electrode modified with bimetallic nanoparticles (NPs) was used for FAOR, which is a key reaction in direct formic acid fuel cells (DFAFCs). Electrodeposits were characterized by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX) to determine diameters, morphology and analysis of elements that make up the bimetallic NPs.

Using a Boron‐Doped Diamond Electrode in Anionic Surfactant Media as an Improved Electrochemical Sensor for the Anticancer Drug Ibrutinib

AbstractThe electrochemical properties of ibrutinib (IBR), a new generation smart anti‐cancer drug, one of the Bruton's tyrosine kinase (BTK) inhibitors were investigated by a voltammetric method in the anionic surfactant (sodium dodecyl sulfate, SDS) medium with the boron‐doped diamond electrode (BDDE). IBR showed an oxidation step at about +1.56 V (vs Ag/AgCl (3.0 mol L−1 KCl) by cyclic voltammetry (CV) technique in 0.1 mol L−1 H2SO4 solution. IBR was found to be irreversible and diffusion‐controlled on the surface of the BDDE with studies of scan rate. The possible electrochemical oxidation reaction of IBR with the electroactive ring (pyrazole‐pyrimidine ring) in the structure of IBR is discussed. Square wave voltammetry (SWV) was preferred as the study method due to reproducibility for the determination of IBR in pharmaceutical and urine samples. At optimal values of SWV parameters, IBR showed good linearity in the concentration range of 0.01–2.00 μg mL−1 (5.7×10−8–2.3×10−6 mol L−1) in 0.1 mol L−1 H2SO4 with 6×10−4 M SDS. The detection (LOD) and quantification (LOQ) limits for IBR were set at 0.003 μg mL−1 (6.9×10−9 mol L−1) and 0.01 μg mL−1 (2.27×10−8 mol L−1), respectively. The relative standard deviation of the intra‐day and inter‐day repeatability of the proposed method was found 2.15 and 3.76, respectively. The necessary validation parameters have also been studied, and the recovery results obtained from both pharmaceutical dosage form and human urine samples show that the developed method is accurate and precise.

Understanding the hydroxyl adsorption behavior at Pt electrode surface in high-temperature alkaline solutions

Since the application in fuel cell, the electrochemical adsorption of hydroxyl has received considerable attention in recent years. While most research mainly focus on the room temperature, in this paper, the electrochemical adsorption of hydroxyl in alkaline solution at high temperature was investigated. An unusual oxidation peak was observed at −0.27 V, suggesting new behavior of hydroxyl adsorption occurred. As is known two kinds of cation hydrated clusters exist in alkaline solution, (H 2 O) x− 1 M + --H 2 O--O ad H and (H 2 O) x M + --O ad H. For K + and Cs + , the cluster shows unstable structure due to the weak interaction between hydrated cation and OH − especially at high temperature. However, For Li + , Na + the cluster structure would be stable, as the interaction force between the hydrated cation and OH − is so strong. It was revealed that the unusual oxidation peak has some relationship with the (H 2 O) x −1 M + --H 2 O--O ad H cluster (K + and Cs + ) absorbed at Pt electrode surface. When the temperature was raised, (H 2 O) x −1 M + --H 2 O- and -O ad H was disconnected, then the O ad H absorbed at Pt surface got oxidated. Based on the SEM observation, it was showed the unusual electrochemical oxidation reaction would generate platinum oxides, blocking the reactive sites at Pt electrode surface, thus reducing the electrochemical reactivity of Pt electrode. Accordingly, parameters of alkaline concentration and temperature were systematically studied, it was found that increase temperature or alkaline concentration was in favor of the unusual oxidation reaction. This study provides more understanding of hydroxyl adsorption behavior at Pt electrode surface for the high temperature water solution environment.