Kinetics Of Oxidation Reaction Research Articles

Combustion of the banana Pseudo-stem hydrochar by the High-Pressure CO2-Hydrothermolysis: Thermal conversion, kinetic, and emission analyses

Due to slow degradation and potentially carrying fungus of banana pseudo-stem, the irresponsibly disposed (such as optionally dumping and burning on the spot) of banana pseudo-stem caused severe environmental problems and fungus disease. However, the combustion efficiency of the banana pseudo-stem was limited by the higher moisture and lower heating value. The high-pressure CO2-hydrothermolysis provides an efficient strategy for upgrading the fuel quality and combustion characteristics. In this study, the combustion characteristics and emission analyses of the sample after and before treatment were investigated by TG–FTIR. Meanwhile, the oxidation reaction kinetics of the sample was established using the Friedman method. The results showed that the “coal-like” fuel, higher heating value (HHV) between 13.64 and 25.76 MJ/kg, was produced from banana pseudo-stem by the high-pressure CO2-hydrothermolysis. The ignition temperature of the sample after treatment is higher than that of the banana pseudo-stem. However, the combustion character index of the sample after treatment at 160 °C (BP-160) is the best among all samples, but that of the sample after treatment at 280 °C (BP-280) is the lowest. The sample after treatment has the higher combustion reactivity except for BP-280. The averaged activation energy values of the sample after treatment decrease with the increased temperature and are higher than that of BP, except for BP-280. The carbon emission (CO2 + CO), SO2 and N species emission (NO + N2O) was reduced during sample combustion after treatment. Overall, the high-pressure CO2-hydrothermolysis is a promising treatment technology for minimizing and energy utilization of banana waste.

Synthesis of keto-biomacromolecule derivatives by oxidation of carboxymethyl cellulose using alkaline hexacyanoferrate (III) for alternative applications in biotechnology

The oxidation kinetics of polysaccharides involving carboxymethyl cellulose (CMC) by several oxidizing agent have been investigated in more detail with shedding some light on the synthesis of their respective keto-derivatives as oxidation precursor products. However, the literature survey indicated that no reports have appeared on the oxidation kinetics of CMC or the synthesis of keto-CMC using hexacyanoferrate (III) ion. Therefore, a lack of information on the transfer of electron process in the rate-determining stage as well as the nature of such keto-derivatives obtained as a result of polysaccharides oxidation using various oxidants in aqueous solutions.Accordingly, the present study presents synthesis of diketo CMC as a biomacromolecule derivative using potassium ferricyanide in alkaline media. The experimental results revealed the formation of either monoketo or diketo-derivatives of CMC based on initial molar ratio between the two reactants. The formation of such keto derivatives was confirmed by the reaction of the oxidation products with both 2,4-dinitrophenyl hydrazine and hydroxyl amine as well as FTIR spectra. The reaction kinetics of oxidation showed unity order in [Fe(CN)63−] and fractional first-orders with respect to both [CMC] and [OH−].The obedience of the reaction behavior to the Michael-Menten kinetics was indicative to the formation of 1:1 intermediate complex prior to the rate-determining step as a pathway route for oxidation.

Reaction kinetics of OH radicals with 1,3,5-trimethyl benzene: An experimental and theoretical study

Alkylated aromatics are ubiquitous in transportation fuels. 1,3,5-Trimethyl benzene (135TMB) is a popular surrogate for the aromatic content of distillate fuels due to its symmetry (point group, C3h), which facilitates the construction of an accurate chemical kinetic model. The reaction of OH radicals with 135TMB plays a crucial role in the oxidation kinetics of 135TMB. In this work, the reaction kinetics of OH-initiated oxidation of 135TMB were investigated behind reflected shock waves over 975–1318 K and atmospheric pressure. The reaction was followed by monitoring OH radicals near 307 nm. The rate coefficients were extracted from detailed chemical kinetic modeling of OH concentration-time profiles. Our measured data clearly showed a positive temperature dependence, in contrast to the negative temperature dependence of the literature low-temperature data. At 1000 K, our measured rate coefficient is 1.3 × 10−11 cm3 molecule−1 s−1, which is roughly a factor of 5 lower than the room-temperature data reported in the literature. This observation reflects the complex nature of the OH + 135TMB reaction, similar to that observed for various aromatics + OH chemical systems. Our measurements did not show any discernible pressure dependence over the narrow pressure range of 870 – 1148 Torr. The title reaction has several possible channels in the reactive potential energy surface. The importance of each channel was characterized using ab initio/RRKM-ME calculations over T = 200–2000 K and P = 0.76 -7600 Torr. Our analyses revealed that addition channels and hydrogen abstraction from the methyl site have negative energy barriers. The reaction was found to undergo almost exclusively (∼93%) via the addition channel under ambient conditions. However, beyond 600 K, the abstraction channels take the lead, yielding the positive T-dependence of the overall rate coefficient. Although addition channels display a sharp fall-off behavior beyond 500 K, the general rate coefficients are pressure-independent. The title reaction shows a complex kinetic behavior due to competing channels whose contribution changes significantly with temperature. Our theoretical calculations nicely reproduced the complex T-dependence of the reaction. After adjusting the barrier height, our theory remarkably captured the positive T-dependence of our high-T kinetic data and the negative T-dependence of the low-T literature data. To our knowledge, this is the first detailed study on the reaction kinetics of 135TMB with OH radicals. The reported rate data will be helpful for the combustion modeling of alkylated aromatic species.

Accelerated kinetics of hydrogen oxidation reaction on the Ni anode coupled with BaZr0.9Y0.1O3-δ proton-conducting ceramic electrolyte via tuning the electrolyte surface chemistry

Owing to the promise of proton mobility in solids, proton ceramic fuel cells (PCFCs) have demonstrated their great potential for operating at the low temperature range of 400-600˚C. For speeding up electrode reactions in PCFCs, the kinetics of the hydrogen oxidation reaction (HOR) on the Ni anode coupled with BaZr0.9Y0.1O3-δ (BZY10) proton-conducting ceramic electrolyte (abbreviated as Ni/BZY10) was investigated in correlation to the electrolyte surface chemistry. It was found that thermal annealing treatments are an effective approach to tune the surface chemistry of BZY10 (ABO3 perovskite structure) electrolytes, resulting in progressively Ba segregation toward the outer surface and enriched Y cations in B-site at subsurface. As the post-annealing temperature of BZY10 electrolytes increase from 600˚C to 1500˚C, the polarization resistance for the corresponding BZY10-based half cells decreases by a factor of 3 and 6 at the testing condition of open circuit potential and anodic overpotential, respectively. Considering a core-space-charge layer model at the Ni/BZY10 interface, the segregation of net charged Y cations (YZr') at the subsurface can partially counterbalance the positive electric potential induced by accumulation of protons in the outer surface, led to a reduced electrical potential and thus the accelerated HOR kinetics on the Ni/BZY10.

Surface defects engineering of BiFeO3 films for improved photoelectrochemical water oxidation

As a promising material for photoelectrochemical (PEC) water oxidation, the fast recombination rate and sluggish surface reaction for BiFeO3 (BFO) still hinder its practical application. In this work, nitrogen plasma was first used to engineer surface defects of the pulsed laser deposition (PLD)-fabricated BFO films to suppress the surface charge recombination and improve the surface water oxidation activity, as well as enhance the stability. A remarkable photocatalytic activity enhancement was observed after the surface modification. Specifically, the photocurrent density is 95 μA/cm2 at 0.6 V (vs. Ag/AgCl, pH=12.8) for BFO–N (after nitrogen plasma treatment), which is about 8 times higher than as-grown BFO (12 μA/cm2) at the same potential. Meanwhile, the onset potential of BFO–N shifts toward the negative value by 120 mV compared to BFO. Also, the BFO–N reveals superior stability to BFO, which shows nearly no decay after the 1-h test. Complete experimental characterization and deep mechanistic analysis indicate that the enhanced performance could be due to the newly-formed Fe-enriched oxynitride layer on the surface after nitrogen plasma treatment, which suppresses the fast recombination, improves the water oxidation reaction kinetics, and protects the photoanode against photocorrosion. Our work offers a simple, but effective way to improve the PEC performance of BFO, which is instructive for fabricating similar high-performance photoelectrodes for PEC applications.

Improving Alkaline Hydrogen Oxidation Activity of Palladium through Interactions with Transition-Metal Oxides

Anion-exchange membrane fuel cells (AEMFCs) are a promising electrochemical power generation technology that will most likely find applications in stationary power supply and mobile applications such as electric vehicles in the future. One of the main technological challenges with AEMFCs is developing catalysts with improved activities to reduce the current overpotential losses in the cell. A historically underappreciated challenge for AEMFC catalyst development is the sluggish hydrogen oxidation reaction (HOR) kinetics at the anode that still requires high loadings of platinum group metals. Here, we demonstrate that the alkaline HOR activity of palladium nanoparticles is enhanced through strong interactions with transition-metal oxides. A series of transition-metal oxides in the IV oxidation state (ZrO2, CeO2, SnO2, and RuO2) were deposited onto Vulcan XC-72 carbon. Pd nanoparticles (20 wt %) were then grown on each support. This series of catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The alkaline HOR activity was investigated using cyclic voltammetry and linear sweep voltammetry. Of the several systems that were considered, Pd–RuO2/C displayed the highest HOR surface-specific activity (49 μA cmPd–2). It had an onset for CO electro-oxidation at around 200 mV, which is lower than the other materials analyzed herein. The results were explained using first-principles calculations by investigating Tafel and Volmer reactions. These results suggested that increased HOR activity is favored by the population of the Pd surface with OH– groups at lower overpotentials. These insights are valuable for the future design of next-generation catalysts with high activity toward alkaline HOR required by future high-performance AEMFCs.

The Role of Hydroxide Binding Energy in Alkaline Hydrogen Oxidation Reaction Kinetics on RuCr Nanosheet†

Comprehensive SummaryUnveiling the role of adsorbed hydroxide involved in the hydrogen oxidation reaction (HOR) under alkaline electrolyte is crucial for the development of advanced HOR electrocatalysts for the alkaline polymer electrolyte fuel cells (APEFCs). Herein, we report the synthesis of amorphous RuCr nanosheets with different molar ratios and their HOR performances under alkaline media. We find a volcano correlation between the Cr content in RuCr nanosheets and their alkaline HOR performance. Experimental results and density functional theory (DFT) calculation reveals that the optimized Cr content in RuCr nanosheets could lead to the optimum hydroxide binding energy (OHBE), contributes to their remarkable alkaline HOR performance with mass activity of 568.1 A·gPGM–1 at 50 mV, 13‐fold higher than that of Ru catalyst. When RuCr nanosheet is further used as the anodic electrocatalyst, a peak power density of 1.04 W·cm–2 can be achieved in an APEFC.

Prussian Blue Type Cocatalysts for Enhancing the Photocatalytic Water Oxidation Performance of BiVO4.

The efficiency of photocatalytic overall water splitting reactions is usually limited by the high energy barrier and complex multiple electron-transfer processes of the oxygen evolution reaction (OER). Although bismuth vanadate (BiVO4 ) as the photocatalyst has been developed for enhancing the kinetics of the water oxidation reaction, it still suffers from challenges of fast recombination of photogenerated electron-hole pairs and poor photocatalytic activity. Herein, six MII -CoIII Prussian blue analogues (PBAs) (M=Mn, Fe, Co, Ni, Cu and Zn) cocatalysts are synthesized and deposited on the surface of BiVO4 for boosting the surface catalytic efficiency and enhancing photogenerated carries separation efficiency of BiVO4 . Six MII -CoIII PBAs@BiVO4 photocatalysts all demonstrate increased photocatalytic water oxidation performance compared to that of BiVO4 alone. Among them, the Co-Co PBA@BiVO4 photocatalyst is employed as a representative research object and is thoroughly characterized by electrochemistry, electronic microscope as well as multiple spectroscopic analyses. Notably, BiVO4 coupling with Co-Co PBA cocatalyst could capture more photons than that of pure BiVO4 , facilitating the transfer of photogenerated charge carriers between BiVO4 and Co-Co PBA as well as the surface catalytic efficiency of BiVO4 . Overall, this work would promote the synthesis strategy development for exploring new types of composite photocatalysts for water oxidation.

Suppressing Electron Back‐Donation for a Highly CO‐tolerant Fuel Cell Anode Catalyst via Cobalt Modulation

AbstractPlatinum on carbon (Pt/C) catalyst is commercially adopted in fuel cells but it undergoes formidable active‐site poisoning by carbon monoxide (CO). In particular, given the sluggish kinetics of hydrogen oxidation reaction (HOR) in anion‐exchange membrane fuel cell (AEMFC), the issues of Pt poisoning and slow rate would combine mutually, notably worsening the device performances. Here we overcome these challenges through incorporating cobalt (Co) into molybdenum‐nickel alloy (MoNi4), termed Co‐MoNi4, which not only shows superior HOR activity over the Pt/C catalyst in alkali, but more intriguingly exhibits excellent CO tolerance with only small activity decay after 10 000 cycles in the presence of 500 parts per million (ppm) CO. When feeding with CO (250 ppm)/H2, the AEMFC assembled by this catalyst yields a peak power density of 394 mW cm−2, far exceeding the Pt/C catalyst. Experimental and computational studies reveal that weakened CO chemisorption originates from the electron‐deficient Ni sites after Co incorporation that suppresses d→CO 2π* back‐donation.

In situ construction of Fe3O4@FeOOH for efficient electrocatalytic urea oxidation

Substituting water oxidation half of water splitting with anodic oxidation of urea can reduce the cost of H2 production and provide an avenue for treating urea-rich wastewater. However, developing an efficient and stable electrocatalyst is necessary to overcome the indolent kinetics of the urea oxidation reaction (UOR). Accordingly, we have used the Schikorr reaction to deposit Fe3O4 particles on the nickel foam (Fe3O4/NF). Results from the various analysis indicated that under the operational conditions, Fe3O4 underwent surface reconstruction to produce a heterolayered structure wherein a catalytically active FeOOH layer encased a conducting Fe3O4. Fe3O4/NF outperformed RuO2 as a UOR catalyst and delivered a current density of 10 50 and 100 mA cm−2 at low applied potentials of 1.38 1.42 and 1.46 V, respectively, with a Tafel slope of 28 mV dec−1. At the applied potential of 1.4 V, Fe3O4/NF demonstrated a turnover frequency (TOF) of 2.8 × 10−3 s−1, highlighting its superior intrinsic activity. In addition, a symmetrical urea electrolyzer constructed using Fe3O4/NF produced the current density of 10 mA cm−2 at a cell voltage of 1.54 V.

Ternary PtRuTe alloy nanofibers as an efficient and durable electrocatalyst for hydrogen oxidation reaction in alkaline media

Sluggish kinetics of anodic hydrogen oxidation reaction (HOR) in alkaline media, which arises from the two orders of magnitude lower HOR activity in alkali than that in acid media for platinum group metals, hinders the commercial implementation of anion exchange membrane fuel cells (AEMFCs). Consequently, the development of platinum-based catalysts combined with high efficiency and durability is urgently required. Herein, we report a facile route for the synthesis of ternary PtRuTe alloy nanofibers with Pt atomic ratio of only 11% via a simple galvanic replacement reaction. We optimize the adsorption strength of platinum and ruthenium towards hydrogen and hydroxyl species by regulating the electron donation from tellurium to platinum and ruthenium. Hence, the obtained trimetallic alloy catalyst exhibits an impressive kinetic current density of 30.6 mA cm−2geo at 50 mV and an exchange current density of 0.426 mA cm−2metal, which shows 3.0- and 2.5-fold enhancement compared with the commercial Pt/C in alkaline electrolyte, respectively. Moreover, the catalyst also demonstrates excellent stability with merely 5% activity attenuation after 2000 potential cycles. This work offers new pathways to boost alkaline HOR by rationally designing multicomponent alloys.

Design and simulation for improved performance via pump‐less direct ethanol fuel cell for mobile application

The advancement of direct ethanol fuel cells (DEFCs) as portable power sources demonstrated a significant challenge since the power output is still far from the acceptable standards, mainly due to the slow kinetics of the ethanol oxidation reaction (EOR) via the passive mode. While the active system presented higher power output but ends up with a bulky system including all the external mechanical devices. Thus, this work proposed a pump-less DEFC to replace the conventional passive and active DEFC systems to achieve both power generation and device portability. The electrochemical results showed that pump-less DEFCs generated comparable power output with active-feed DEFCs. Computational fluid dynamic (CFD) simulations of the anode flow field for pump-less DEFCs were carried out using three types of flow field designs with different fuel outlet directions. The results indicated that a winding outlet (L-shaped) channel produced the lowest fuel discharge velocity as a result of a high static pressure drop along the channel.

Thermochemistry and Kinetics of the Atmospheric Oxidation Reactions of Propanesulfinyl Chloride Initiated by OH Radicals: A Computational Approach.

The thermochemistry and kinetics of the atmospheric oxidation mechanism for propanesulfinyl chloride (CH3-CH2-CH2-S(═O)Cl; PSICl) initiated by the hydroxyl (OH) radical were investigated with high level quantum chemistry calculations and the Master equation solver for multi-energy well reaction (Mesmer) kinetic code. The mechanism for the oxidation of PSICl in the presence of OH radical can proceed via H-abstraction and substitution pathways. The CCSD(T)/aug-cc-pV(T+d)Z//MP2/aug-cc-pV(T+d)Z level calculated energies revealed addition of the OH radical to the S-atom of the sulfinyl (-S(═O)) moiety, followed by cleavage of the Cl-S(═O) single bond, leading to formation of propanesulfinic acid (PSIA) and the Cl radical to be the major pathway when compared to all other possible channels. The transition state barrier height for this reaction was found to be -3.0 kcal mol-1 relative to the energy of the starting PSICl + OH radical reactants. The rate coefficients were calculated for all possible paths in the atmospherically relevant temperature range of 200-320 K and at 1 atm. The rate coefficient for the formation of the PSIA + Cl radical from the PSICl + OH radical reaction was found to be 8.2 × 10-12 cm3 molecule-1 s-1 at 298 K and a pressure of 1 atm. From branching ratio calculations, it was revealed that the reaction resulting in the formation of the PSIA + Cl radical contributed ∼52% to the total reaction. The overall rate coefficient for the PSICl + OH reaction was also calculated and found to be 1.6 × 10-11 cm3 molecule-1 s-1 at 298 K and a pressure of 1 atm. In the aggregate, the results indicate the atmospheric lifetime of PSICl to be ∼12-20 h in the temperature range between 200 and 320 K, which suggests that its contribution to global warming is negligible. However, the degradation products revealed to be formed in its interactions with the OH radical, which include that SO2, Cl radical, HO2 radical, and propylene have significant effects on the formation of acid rain, secondary organic aerosols, the ozone layer, and global warming.

Design of Ru-Ni diatomic sites for efficient alkaline hydrogen oxidation.

Anion exchange membrane fuel cells are limited by the slow kinetics of alkaline hydrogen oxidation reaction (HOR). Here, we establish HOR catalytic activities of single-atom and diatomic sites as a function of *H and *OH binding energies to screen the optimal active sites for the HOR. As a result, the Ru-Ni diatomic one is identified as the best active center. Guided by the theoretical finding, we subsequently synthesize a catalyst with Ru-Ni diatomic sites supported on N-doped porous carbon, which exhibits excellent catalytic activity, CO tolerance, and stability for alkaline HOR and is also superior to single-site counterparts. In situ scanning electrochemical microscopy study validates the HOR activity resulting from the Ru-Ni diatomic sites. Furthermore, in situ x-ray absorption spectroscopy and computational studies unveil a synergistic interaction between Ru and Ni to promote the molecular H2 dissociation and strengthen OH adsorption at the diatomic sites, and thus enhance the kinetics of HOR.

Artificial neural networks modeling ethanol oxidation reaction kinetics catalyzed by polyaniline-manganese ferrite supported platinum-ruthenium nanohybrid electrocatalyst

The electrochemical and physicochemical properties of the anode catalyst used in alcohol fuel cells affect the efficiency of the fuel cell due to both its effect on the cell potential and its direct relationship with the reaction stoichiometry. It is possible to determine these parameters from polarization curves (current vs. cell potential) of the cells. At low potentials, Tafel plots offer kinetic information, whereas currents at high potentials reveal the average number of electrons released per ethanol molecule and their potential dependency. Herein, bearing the chemical engineering research and design aspects, it was aimed to model the kinetics of ethanol electrooxidation reaction catalyzed by PANI-MnFe2O4/Pt/Ru nanocomposite by an artificial neural network (ANN) approach, specifically by Differential Evolution (DE) algorithm for the first time. The different parts of the Tafel plots were condensed into a single and efficient model to illustrate the generalization potential of ANN. The findings demonstrated that the best model with a single hidden layer with 18 neurons offered the highest correlation metrics of 0.997476, and the lowest mean-square-error value of 0.000428 at the testing phase. Furthermore, the average absolute error was calculated, with 0.773% in the training phase and 0.66% in the testing phase. These outstanding results indicated that the best model is capable of accurately capturing the dynamics of all instances analyzed.

Comparison of combustion characteristics and kinetics of Jurassic and Carboniferous-Permian coals in China

The study of combustion characteristics and kinetic parameters plays an important role in the determination of the coal fire combustion regime. Four Chinese coals from the Jurassic and Carboniferous-Permian periods were selected to study the influence of the geological time on the coal combustion characteristics. The thermogravimetry and differential scanning calorimetry with different heating rates were employed to identify the combustion characteristics and oxidation reaction kinetics of coal samples. It was found that a high heating rate could boost the characteristic temperatures of coal, and the curves characteristics of thermogravimetry and differential scanning calorimetry of all coal samples were the same. The ignition temperatures of coals from the Carboniferous-Permian period were lower than that of coals from the Jurassic period. During the coal combustion stage, the heat release of the Carboniferous-Permian coal samples was 166.86–2423.84 J/g, higher than that of the Jurassic coal samples. By Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink methods, it was found that the activation energy required for combustion reaction of Carboniferous-Permian coals was 37.18–88.95 kJ/mol, lower than that of Jurassic coals, revealing that the combustion performance of Carboniferous-Permian coals was superior to that of Jurassic coals.

Spectroelectrochemistry of Water Oxidation Kinetics in Molecular versus Heterogeneous Oxide Iridium Electrocatalysts.

Water oxidation is the step limiting the efficiency of electrocatalytic hydrogen production from water. Spectroelectrochemical analyses are employed to make a direct comparison of water oxidation reaction kinetics between a molecular catalyst, the dimeric iridium catalyst [Ir2(pyalc)2(H2O)4-(μ-O)]2+ (IrMolecular, pyalc = 2-(2′pyridinyl)-2-propanolate) immobilized on a mesoporous indium tin oxide (ITO) substrate, with that of an heterogeneous electrocatalyst, an amorphous hydrous iridium (IrOx) film. For both systems, four analogous redox states were detected, with the formation of Ir(4+)–Ir(5+) being the potential-determining step in both cases. However, the two systems exhibit distinct water oxidation reaction kinetics, with potential-independent first-order kinetics for IrMolecular contrasting with potential-dependent kinetics for IrOx. This is attributed to water oxidation on the heterogeneous catalyst requiring co-operative effects between neighboring oxidized Ir centers. The ability of IrMolecular to drive water oxidation without such co-operative effects is explained by the specific coordination environment around its Ir centers. These distinctions between molecular and heterogeneous reaction kinetics are shown to explain the differences observed in their water oxidation electrocatalytic performance under different potential conditions.

Rhodium–Cobalt Alloy Nanotubes Toward Methanol Oxidation Reaction

The sluggish reaction kinetics of the anodic methanol oxidation reaction (MOR) seriously hinders the commercial development of direct methanol fuel cells. Considering the vital role of catalysts, this work focuses on the synthesis of rhodium–cobalt alloy nanotubes (RhCo‐NTs) through a simple one‐pot reduction approach using hydrazine hydrate as a reducing agent. RhCo‐NTs with different Rh/Co atomic ratios can be handily achieved by simply controlling RhIII/CoII feeding proportions. The hollow and tubular architecture of RhCo‐NTs gains abundant boundary/defect atoms, improves the atomic utilization of Rh, and enlarges the valid connection between active sites and reactants. Compared with commercial Rh nanocrystals, RhCo‐NTs with optimized Rh/Co atomic ratio show sharply enhanced MOR electroactivity and long‐term stability because of the particular tubular morphology, big electrochemical active area, suitable Co introduction, excellent self‐stability, and eminent anti‐poison capability.

Co-Ni Layered Double Hydroxide for the Electrocatalytic Oxidation of Organic Molecules: An Approach to Lowering the Overall Cell Voltage for the Water Splitting Process.

Electrocatalytic oxidation of simple organic molecules offers a promising strategy to combat the sluggish kinetics of the water oxidation reaction (WOR). The low potential requirement, inhibition of the crossover of gases, and formation of value-added products at the anode are benefits of the electrocatalytic oxidation of organic molecules. Herein, we developed cobalt-nickel-based layered double hydroxide (LDH) as a robust material for the electrocatalytic oxidation of alcohols and urea at the anode, replacing the WOR. A facile synthesis protocol to form LDHs with different ratios of Co and Ni is adapted. It demonstrates that the reactants could be efficiently oxidized to concomitant chemical products at the anode. The half-cell study shows an onset potential of 1.30 V for benzyl alcohol oxidation reaction (BAOR), 1.36 V for glycerol oxidation reaction (GOR), 1.33 V for ethanol oxidation reaction (EOR), and 1.32 V for urea oxidation reaction (UOR) compared with 1.53 V for WOR. Notably, the hybrid electrolyzer in a full-cell configuration significantly reduces the overall cell voltage at a 20 mA cm-2 current density by ∼15% while coupling with the BAOR, EOR, and GOR and ∼12% with the UOR as the anodic half-cell reaction. Furthermore, the efficiency of hydrogen generation remains unhampered with the types of oxidation reactions (alcohols and urea) occurring at the anode. This work demonstrates the prospects of lowering the overall cell voltage in the case of a water electrolyzer by integrating the hydrogen evolution reaction with suitable organic molecule oxidation.

A core-shell NiCu@NiCuOOH 3D electrode induced by surface electrochemical reconstruction for the ammonia oxidation reaction

A direct ammonia microfluidic fuel cell is a potential portable carbon-free clean energy device. In this work, a NiCu-based core-shell 3D electrode is obtained by electrodeposition and surface electrochemical reconstruction on the nickel foam substrate. The physical characterization results confirm the core-shell structure with NiCu as the core and Cu(OH)2 and NiOOH as the shell. In the 3D electrode, the metal core continuously transfers charge to the surface to transform into active species (NiCu hydroxides), thus accelerating the slow ammonia oxidation reaction kinetics. Furthermore, the 3D porous structure is conducive to the rapid diffusion and transport of ions, which effectively improves the fuel depletion boundary layer problem. Consequently, electrochemical tests indicate that the NiCu@NiCuOOH-NF electrode show excellent ammonia oxidation reaction activity and good stability, reaching a maximum current density of 90 mA cm−2 at the potential of 0.7 V vs. saturated calomel electrode (SCE). When 2 M NaOH + 3 M NH4Cl is adopted as fuel for the DAMFC, an open circuit voltage of 0.72 V and a peak power density of 17.1 mW cm−2 can be obtained, while the limiting current density is as high as 102 mA cm−2.