A Lattice‐Oxygen‐Involved Reaction Pathway to Boost Urea Oxidation

The electrocatalytic urea oxidation reaction (UOR) provides more economic electrons than water oxidation for various renewable energy‐related systems owing to its lower thermodynamic barriers. However, it is limited by sluggish reaction kinetics, especially by CO₂ desorption steps, masking its energetic advantage compared with water oxidation. Now, a lattice‐oxygen‐involved UOR mechanism on Ni⁴⁺ active sites is reported that has significantly faster reaction kinetics than the conventional UOR mechanisms. Combined DFT, ¹⁸O isotope‐labeling mass spectrometry, and in situ IR spectroscopy show that lattice oxygen is directly involved in transforming *CO to CO₂ and accelerating the UOR rate. The resultant Ni⁴⁺ catalyst on a glassy carbon electrode exhibits a high current density (264 mA cm^?2 at 1.6 V versus RHE), outperforming the state‐of‐the‐art catalysts, and the turnover frequency of Ni⁴⁺ active sites towards UOR is 5 times higher than that of Ni³⁺ active sites.     

Study on Electrocatalytic Oxidation of L‐Cysteine at Glassy Carbon Electrode by (FcM)TMA and Its Electrochemical Kinetics

The electrocatalytic oxidation of L ‐cysteine by (ferrocenylmethyl)trimethylammonium at a glassy carbon electrode in 0.1 M Na₂SO₄ aqueous solution has been studied. The rate constant for the catalytic reaction was evaluated as (4.28±0.05)×10³ M^?1 s^?1 by chronoamperometry. Experimental conditions, which maximize the current efficiency of the electrocatalytic oxidation, such as pH value and the concentration of the catalyst, were also investigated. The experimental results of electrocatalytic kinetics of L ‐cysteine oxidation on GCE in the presence of (ferrocenylmethyl)trimethylammonium obviously support the reaction mechanism proposed and the rate determining step assumed in scheme described in this work.     

Atomically Dispersed Nickel(I) on an Alloy‐Encapsulated Nitrogen‐Doped Carbon Nanotube Array for High‐Performance Electrochemical CO2 Reduction Reaction

Single‐atom catalysts (SACs) show great promise for electrochemical CO₂ reduction reaction (CRR), but the low density of active sites and the poor electrical conduction and mass transport of the single‐atom electrode greatly limit their performance. Herein, we prepared a nickel single‐atom electrode consisting of isolated, high‐density and low‐valent nickel(I) sites anchored on a self‐standing N‐doped carbon nanotube array with nickel–copper alloy encapsulation on a carbon‐fiber paper. The combination of single‐atom nickel(I) sites and self‐standing array structure gives rise to an excellent electrocatalytic CO₂ reduction performance. The introduction of copper tunes the d‐band electron configuration and enhances the adsorption of hydrogen, which impedes the hydrogen evolution reaction. The single‐nickel‐atom electrode exhibits a specific current density of ?32.87 mA cm^?2 and turnover frequency of 1962 h^?1 at a mild overpotential of 620 mV for CO formation with 97 % Faradic efficiency.     

Electrochemical Detection of As(III) via Iodine Electrogenerated at Platinum,Gold, Diamond or Carbon‐Based Electrodes

The reaction of iodine, electrogenerated from iodide, is used for the detection of As(III) via electrocatalytic reaction in the diffusion layer of a boron‐doped diamond electrode. The merits of this electrode material for this purpose (over platinum, gold or glassy carbon) are demonstrated and the kinetics of the reaction between I₂ and As(III) in acid reported.     

Electrooxidation of hydrazine catalyzed by 4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy (TEMPOL)

The electrocatalytic oxidation of hydrazine (N₂H₄) by TEMPOL on a glassy carbon electrode has been studied. The kinetic parameters of the electrode reaction were measured and the electrocatalytic reaction mechanism for the electrooxidation of hydrazine in the presence of TEMPOL was proposed. TEMPOL undergoes a reversible single electron transfer process at a glassy carbon electrode (GCE) at pH 1.2–8.0, and the electrochemical oxidation of N₂H₄ at a GCE can be catalyzed by TEMPOL. The catalytic current is affected by the concentration of catalyst and pH. The overall number of electrons involved in the catalytic oxidation of N₂H₄ and the number of electrons involved in the rate determining step (rds) are 4 and 1, respectively. The catalytic oxidation obeys the first-order kinetics with respect to N₂H₄. The proposed mechanism is consistent with the experimental data, and a cation intermediate [> N---O---N₂H₄⁺], formed by reaction of oxoammonium salt with N₂H₄, is involved in the reaction.     

2-Propanol oxidation on platinum and platinum–rhodium electrodeposits

The electrocatalytic oxidation of 2-propanol was investigated using on line differential electrochemical mass spectrometry (DEMS) on electrodeposited Pt and an arrange of bimetallics: Pt_0.84Rh_0.16, Pt_0.70Rh_0.30, Pt_0.55Rh_0.45. It has been observed that the Pt_0.84Rh_0.16 bimetallic electrode presented the best catalytic activity for 2-propanol electrochemical oxidation. Since 2-propanol is a secondary alcohol, only acetone and CO₂ are produced. The total yield of CO₂ and acetone has been determined from the DEMS measurements. It is found that acetone is the major product, as reported before for other electrodes. The acetone and CO₂ yield depends on the electrode composition. High amount of rhodium in the electrode composition strongly diminish the reaction rate as indicated by the decrease of both the acetone and CO₂ yield. However, acetone inhibition is much more intense. The only bimetallic electrode that presents considerable mass spectroscopy signals intensity for CO₂ and acetone is the Pt_0.84Rh_0.16 electrode. This electrode shows a slight increase in CO₂ selectivity, compared to the other electrodes studied in this work. Only very low coverages of stable adsorbates were present during the reaction. Two and one carbon adsorbate were observed for all the electrodes. Three carbon adsorbates were detected only for the Pt_0.84Rh_0.16 electrode. Therefore, acetone production does not require a stable adsorbate.     

Electrocatalytic Production of C3‐C4 Compounds by Conversion of CO2 on a Chloride‐Induced Bi‐Phasic Cu2O‐Cu Catalyst

Electrocatalytic conversion of carbon dioxide (CO₂) has recently received considerable attention as one of the most feasible CO₂ utilization techniques. In particular, copper and copper‐derived catalysts have exhibited the ability to produce a number of organic molecules from CO₂. Herein, we report a chloride (Cl)‐induced bi‐phasic cuprous oxide (Cu₂O) and metallic copper (Cu) electrode (Cu₂O_Cl) as an efficient catalyst for the formation of high‐carbon organic molecules by CO₂ conversion, and identify the origin of electroselectivity toward the formation of high‐carbon organic compounds. The Cu₂O_Cl electrocatalyst results in the preferential formation of multi‐carbon fuels, including n‐propanol and n‐butane C3–C4 compounds. We propose that the remarkable electrocatalytic conversion behavior is due to the favorable affinity between the reaction intermediates and the catalytic surface.     

Electrocatalytic Oxidation of Some Carbohydrates by Nickel/Poly(o‐Aminophenol) Modified Carbon Paste Electrode

This study investigates the electrocatalytic oxidation of glucose and some other carbohydrates on nickel/poly(o‐aminophenol) modified carbon paste electrode as an enzyme free electrode in alkaline solution. Poly(o‐aminophenol) was prepared by electropolymerization using a carbon paste electrode bulk modified with o‐aminophenol and continuous cyclic voltammetry in HClO₄ solution. Then Ni(II) ions were incorporated to electrode by immersion of the polymeric modified electrode having amine group in 1 M Ni(II) ion solution. Cyclic voltammetric and chronoamperometric experiments were used for the electrochemical study of this modified electrode; a good redox behavior of Ni(OH)₂/NiOOH couple at the surface of electrode can be observed, the capability of this modified electrode for catalytic oxidation of glucose and other carbohydrates was demonstrated. The amount of α and surface coverage (Γ*) of the redox species and catalytic chemical reaction rate constant (k) for each carbohydrate were calculated. Also, the electrocatalytic oxidation peak currents of all tested carbohydrates exhibit a good linear dependence on concentration and their quantification can be done easily.     

The Electrocatalytic Oxidation of Thymine at α‐Cyclodextrin Incorporated Carbon Nanotube‐Coated Electrode

Electrocatalytic oxidation of thymine at α‐cyclodextrin (α‐CD) incorporated carbon nanotube‐coated electrode (CNT/CE) was thoroughly studied in alkaline media. CNT showed an electrocatalytic effect on the oxidation of thymine, formation of a supramolecular inclusion complex between α‐CD and thymine at CNT/CE further enhanced the sensitivity to thymine. The electrocatalytic behavior was further developed as a sensitive detection scheme for thymine by differential pulse voltammetry. A linear calibration over the concentration range from 2.5×10^?5 to 1.8×10^?3 mol/L in pH 10.8 NaHCO₃‐Na₂CO₃ buffer solution was obtained with a detection limit of 5×10^?6 mol/L.     

Carboxysome-Inspired Electrocatalysis using Enzymes for the Reduction of CO2 at Low Concentrations**

The electrolysis of dilute CO₂ streams suffers from low concentrations of dissolved substrate and its rapid depletion at the electrolyte-electrocatalyst interface. These limitations require first energy-intensive CO₂ capture and concentration, before electrolyzers can achieve acceptable performances. For direct electrocatalytic CO₂ reduction from low-concentration sources, we introduce a strategy that mimics the carboxysome in cyanobacteria by utilizing microcompartments with nanoconfined enzymes in a porous electrode. A carbonic anhydrase accelerates CO₂ hydration kinetics and minimizes substrate depletion by making all dissolved carbon available for utilization, while a highly efficient formate dehydrogenase reduces CO₂ cleanly to formate; down to even atmospheric concentrations of CO₂. This bio-inspired concept demonstrates that the carboxysome provides a viable blueprint for the reduction of low-concentration CO₂ streams to chemicals by using all forms of dissolved carbon.     

In Situ Scanning Tunneling Microscopy of Cobalt‐Phthalocyanine‐Catalyzed CO2 Reduction Reaction

We report a molecular investigation of a cobalt phthalocyanine (CoPc)‐catalyzed CO₂ reduction reaction by electrochemical scanning tunneling microscopy (ECSTM). An ordered adlayer of CoPc was prepared on Au(111). Approximately 14 % of the adsorbed species appeared with high contrast in a CO₂‐purged electrolyte environment. The ECSTM experiments indicate the proportion of high‐contrast species correlated with the reduction of Co^IIPc (?0.2 V vs. saturated calomel electrode (SCE)). The high‐contrast species is ascribed to the CoPc‐CO₂ complex, which is further confirmed by theoretical simulation. The sharp contrast change from CoPc‐CO₂ to CoPc is revealed by in situ ECSTM characterization of the reaction. Potential step experiments provide dynamic information for the initial stage of the reaction, which include the reduction of CoPc and the binding of CO₂, and the latter is the rate‐limiting step. The rate constant of the formation and dissociation of CoPc‐CO₂ is estimated on the basis of the in situ ECSTM experiment.     

Selective electroreduction of carbon dioxide to formic acid on electrodeposited SnO<Subscript>2</Subscript>@N-doped porous carbon catalysts

Electrocatalytic reduction of CO₂ is a promising route for energy storage and utilization. Herein we synthesized SnO₂ nanosheets and supported them on N-doped porous carbon (N-PC) by electrodeposition for the first time. The SnO₂ and N-PC in the SnO₂@N-PC composites had exellent synergistic effect for electrocatalytic reduction of CO₂ to HCOOH. The Faradaic efficiency of HCOOH could be as high as 94.1% with a current density of 28.4 mA cm^?2 in ionic liquid-MeCN system. The reaction mechanism was proposed on the basis of some control experiments. This work opens a new way to prepare composite electrode for electrochemical reduction of CO₂.     

Kinetics of the reaction of carbon dioxide with blends of amines in aqueous media using the stopped‐flow technique

The effect of mixing 2‐amino‐2‐methyl‐1‐propanol (AMP) with a primary amine, monoethanolamine (MEA), and a secondary amine, diethanolamine (DEA), on the kinetics of the reaction with carbon dioxide in aqueous media has been studied at 298, 303, 308, and 313 K over a range of blend composition and concentration. The direct stopped‐flow conductimetric method has been used to measure the kinetics of these reactions. The proposed model representing the reaction of CO₂ with either of the blends studied is found to be satisfactory in determining the kinetics of the involved reactions. This model is based on the zwitterion mechanism for all the amines involved (AMP, MEA, and DEA). Blending AMP with either of the amines results in observed pseudo‐first‐order reaction rate constant values (k_o) that are greater than the sum of the k_o values of the respective pure amines. This is due to the role played by one amine in the deprotonation of the zwitterion of the other amine. Steric factor and basicity of the formed zwitterion and the deprotonating species have a great bearing in determining the rate of the reactions studied. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 391–405, 2005     

G‐quadruplex Nanowires To Direct the Efficiency and Selectivity of Electrocatalytic CO2 Reduction

DNA as a medium for electron transfer has been widely used in photolytic processes but is seldom applied to dark reaction of CO₂ reduction. A G‐quadruplex nanowire (tsGQwire) assembled by guanine tetranucleotides was used to host several metal complexes and further to mediate electron transfer processes in the electrochemical reduction of CO₂ catalyzed by these complexes. The tsGQwire modified electrode increased the Faradaic efficiency of cobalt(II) phthalocyanine (Co^IIPc) 2.5‐folds for CO production than bare Co^IIPc electrode, with a total current density of 11.5 mA cm^?2. Comparable Faradaic efficiency of HCOOH production was achieved on tsGQwire electrode when the catalytic center was switched to a GQ targeting Ru complex. The high efficiency and selectivity of electrocatalytic CO₂ reduction was attributed to the unique binding of metal complexes on G‐quadruplex and electron transfer mediated by GQ nanowire to achieve efficient redox cycling of catalytic centers on the electrode.     

Rapid Selective Electrocatalytic Reduction of Carbon Dioxide to Formate by an Iridium Pincer Catalyst Immobilized on Carbon Nanotube Electrodes

An iridium pincer dihydride catalyst was immobilized on carbon nanotube‐coated gas diffusion electrodes (GDEs) by using a non‐covalent binding strategy. The as‐prepared GDEs are efficient, selective, durable, gas permeable electrodes for electrocatalytic reduction of CO₂ to formate. High turnover numbers (ca. 54 000) and turnover frequencies (ca. 15 s^?1) were enabled by the novel electrode architecture in aqueous solutions saturated in CO₂ with added HCO₃^?.     

Anthraquinonedisulfonate Doped Polyaniline as an Acceptor‐Donor System for Electrocatalysis of Oxygen Reduction

A stable polyaniline (PANI) film doped with anthraquinonedisulfonate (AQDS) on glassy carbon (GC) electrode is obtained in acidic solution. The electrochemical behavior of PANI/AQDS film coincides with the donor–acceptor (DA) intramolecular interaction, while the doped AQDS behaves as a two‐electron two‐proton transfer process during redox reaction. This GC/PANI/AQDS electrode shows high electrocatalytic activity and irreversible electron‐transfer characteristic for O₂ two‐electron reduction. Tafel behavior analysis suggests that the oxygen reduction kinetics are different at certain potential regions on this electrode. Possible mechanism of oxygen reduction on the GC/PANI/AQDS electrode points to a similar Schottky diode characteristic.     

Catholyte‐Free Electrocatalytic CO2 Reduction to Formate

Electrochemical reduction of carbon dioxide (CO₂) into value‐added chemicals is a promising strategy to reduce CO₂ emission and mitigate climate change. One of the most serious problems in electrocatalytic CO₂ reduction (CO₂R) is the low solubility of CO₂ in an aqueous electrolyte, which significantly limits the cathodic reaction rate. This paper proposes a facile method of catholyte‐free electrocatalytic CO₂ reduction to avoid the solubility limitation using commercial tin nanoparticles as a cathode catalyst. Interestingly, as the reaction temperature rises from 303 K to 363 K, the partial current density (PCD) of formate improves more than two times with 52.9 mA cm^?2, despite the decrease in CO₂ solubility. Furthermore, a significantly high formate concentration of 41.5 g L^?1 is obtained as a one‐path product at 343 K with high PCD (51.7 mA cm^?2) and high Faradaic efficiency (93.3 %) via continuous operation in a full flow cell at a low cell voltage of 2.2 V.     

An EC-FTIR study on the catalytic role of Pt in carbon corrosion

In this study, we investigate the role of Pt in the corrosion of carbon by Fourier-transformed infrared spectroscopy coupled in situ with electrochemical measurements. We confirm that the carbon corrosion rate is strongly enhanced in the presence of Pt and shed light on the reaction mechanisms at both anode and cathode potentials. It is shown that carbon surface oxide species (phenol, ether, carboxylic and carbonyl groups), formed at low electrode potential E < 0.60 V vs. RHE, spillover back from the carbon support to the Pt nanoparticles, where they are converted into CO and then slowly oxidized into CO₂. At higher electrode potential E > 0.60 V vs. RHE, oxygenated species resulting from water splitting on Pt facilitate the removal of these carbon surface oxides species yielding increased kinetics for carbon corrosion.     

Rotating ring-disk voltammetry: Diagnosis of catalytic activity of metallic copper catalysts toward CO<Subscript>2</Subscript> electroreduction

Using the rotating ring (platinum)—disk (glassy carbon) electrode methodology, electrocatalytic activity of the microstructured copper centers (imbedded within the polyvinylpyrrolidone polymer matrix and deposited onto the glassy carbon disk electrode) has been monitored during electroreduction of carbon dioxide both in acid (HClO₄) and neutral (KHCO₃) media as well as diagnosed (at Pt ring) with respect to formation of the electroactive products. Combination of the stripping-type and rotating ring-disk voltammetric approaches has led to the observation that, regardless the overlapping reduction phenomena, the reduction of carbon dioxide at copper catalyst is, indeed, operative and coexists with hydrogen evolution reaction. Using the fundamental concepts of surface electrochemistry and analytical voltammetry, the reaction products (thrown onto the platinum ring electrode) could be considered and identified as adsorbates (on Pt) under conditions of the stripping-type oxidation experiment. Judging from the potentials at which the stripping voltammetric peaks appear in neutral CO₂-saturated KHCO₃ (pH 6.8), formic acid or carbon monoxide seem to be the most likely reaction products or intermediates. The proposed methodology also permits correlation between the CO₂ electroreduction products and the potentials applied to the disk electrode. By performing the comparative stripping-type voltammetric experiments in acid medium (HClO₄ at pH 1) with the adsorbates of formic acid, ethanol and acetaldehyde (on Pt ring), it can be rationalized that, although C₂H₅OH or CH₃CHO are very likely CO₂-reduction electroactive products, formation of some HCOOH, CH₃OH or even CO cannot be excluded.     

The role of catalytic reactions in the generating of electrode potentials in chemically irreversible gas mixtures

The formation of steady-state potential at an electrode of solid-electrolyte electrochemical cell placed in chemically irreversible gas mixture is discussed; the potential emerges due to the change in the gas activities at the electrode, caused by the passing of catalytic reaction. This mechanism of potential change is analyzed theoretically for a catalytically asymmetrical gas-diffusion cell located in a CH₄ + CO + CO₂ gas mixture. Experimental studies demonstrated an agreement between the experimental results and theoretical considerations. Dependence of the potential changing rate on the kinetics of the methane catalytic oxidation is revealed experimentally.