Oxidation Reaction Research Articles

Selective Hydrogen Oxidation Catalyst for PEM Fuel Cells: Tungsten Cluster-Tuned Platinum Single Atoms.

The selective hydrogen oxidation reaction (HOR) electrocatalyst is crucial for enhancing the performance of proton-exchange membrane fuel cells (PEMFCs) against degradation caused by reverse currents. In this study, a catalyst comprising platinum single atoms (Pt1) finely tuned by tungsten nanoclusters (WNC) on an accordion-like nitrogen-doped carbon support (ANC) is presented. The tungsten nanoclusters, derived from phosphotungstic acid, are embedded within the carbon support, while the Pt single atoms are uniformly dispersed on its surface. Experimental results and theoretical calculations reveal that the WNC effectively reduce the hydrogen adsorption strength on Pt1 to an optimal level, thereby facilitating HOR catalysis. Notably, this adjustment also weakens oxygen adsorption, rendering Pt1 less effective for catalyzing the oxygen reduction reaction. Consequently, the catalyst Pt1/WNC-ANC exhibits high resistance to degradation from reverse currents when oxygen leaks into the anode. Meanwhile, it demonstrates an ultralow HOR overpotential with an outstanding mass activity, 13 times greater than commercial Pt/C. This work provides a highly active and selective low-Pt HOR catalyst, paving the way for the development of cost-effective, long-lasting, and robust PEMFCs.

Achieving Excess Hydrogen Output via Concurrent Electrochemical and Chemical Redox Reactions on P-Doped Co-Based Catalysts with Electron Manipulation and Kinetic Regulation.

Electrolytic hydrogen production is of great significance in energy conversion and sustainable development. Traditional electrolytic water splitting confronts high anode voltage with oxygen generation and the amount of hydrogen produced at cathode depends entirely on the quantity of electric charge input. Herein, excess hydrogen output can be achieved by constructing a spontaneous hydrazine oxidation reaction (HzOR) coupled hydrogen evolution reaction (HER) system. For the hydrazine oxidation-assisted electrolyzer in this work, both the external input electrons and the electrons produced by spontaneous chemical redox reaction can reduce water, producing more hydrogen than traditional electrolytic water splitting system. The ultrafast kinetics of bifunctional P-doped Co-based catalysts plays a key role in the spontaneous feature of HzOR/HER redox reaction and low working voltage of hydrazine oxidation-assisted electrolyzer (12 mV@100mA cm-2). Theoretical calculation results and ex situ/in situ spectra demonstrate that doped P could optimize electronic structure, regulate adsorption energy of intermediates, and thus endows catalysts with ultrafast kinetics. This work provides a new pathway for the development of spontaneous oxidation-assisted hydrogen production, to achieve excess hydrogen output via concurrent electrochemical and chemical redox reactions.

Donor-Acceptor Viologens with Through-Space Conjugation for Enhanced Visible-Light-Driven Photocatalysis.

A series of novel donor-acceptor (D-A) type viologens with through-space conjugation (TSC) are synthesized. The synergistic effect of D-A conjugation and TSC endow these compounds with a narrower energy gap, excellent redox properties, strong absorption in the visible range (up to 450nm), and high efficiency of intramolecular charge transfer (ICT). These compounds also exhibit a long-lived charge separation state and stable radical formation. Considering their impressive photophysical and redox properties, TSC viologens with D-A conjugation are explored for visible-light-driven photocatalysis. As a catalyst in oxidative coupling reactions under visible light, compound 9 can achieve a yield of 94%, attributed to its strong ICT effect. Additionally, hybridized into graphitic carbon nitride (g-C₃N₄), compound 9 enhances hydrogen production performance under visible light, achieving an H2 generation rate of 4102µmolh-1g-1. This study highlights the potential applications of TSC viologens in photocatalytic systems.

Polymer Networks Assembled by Ruthenium Catalysts for Enhanced Water Splitting Performance in Calixarene Dye-Sensitized Photoelectrochemical Cells.

Metal-free photosensitizers for the construction of low-cost and eco-friendly dye-sensitized photoelectrochemical cells (DSPECs) have recently been greatly improved, but the optimization of water oxidation catalysts (WOCs) used in DSPECs based on metal-free dyes has received little attention. Herein, a series of polymer networks (RuTPA, RuCz, RuPr and RuTz) assembled by ruthenium WOCs (RuCHO) with various organic donors are constructed and combined with calixarene dyes to prepare DSPEC devices. The FTO|TiO2|C4BTP+RuTPA photoanode shows the best performance with 85% Faraday efficiency for oxygen production and 477 μA cm-2 photocurrent density after 200 s chopping irradiation at 0 V vs. Ag/AgCl, one of the highest records among other reported dye-sensitized photoanodes. Compared to monomeric RuCHO, Ru-based polymers with lower Ru content have higher activity and stability due to their rapid electron transfer and anti-aggregation ability. Meanwhile, RuTPA loaded electrodes show better performance due to the lower overpotential of the water oxidation reaction caused by the higher electron donating ability of its donor. This pioneering work incorporates Ru polymer networks as WOCs into the calixarene-sensitized DSPEC system, which has significant potential as a highly efficient and stable photoelectrochemical water splitting device.

Oxidation of four monoterpenoid indole alkaloid classes by three cytochrome P450 monooxygenases from Tabernaemontana litoralis.

Cytochrome P450 monooxygenases (CYPs) are well known for their ability to catalyze diverse oxidation reactions, playing a significant role in the biosynthesis of various natural products. In the realm of monoterpenoid indole alkaloids (MIAs), one of the largest groups of alkaloids in nature, CYPs are integral to reactions such as hydroxylation, epoxidation, ring opening, ring rearrangement, and aromatization, contributing to the extensive diversification of these compounds. In this study, we investigate the transcriptome, metabolome, and MIA biosynthesis in Tabernaemontana litoralis (milky way tree), a prolific producer of rare pseudoaspidosperma-type MIAs. Alongside known pseudoaspidosperma biosynthetic genes, we identify and characterize three new CYPs that facilitate regio- and stereospecific oxidation of four MIA skeletons: iboga, aspidosperma, pseudoaspidosperma, and quebrachamine. Notably, the tabersonine 14,15-β-epoxidase catalyzes the formation of pachysiphine, the stereoisomer of 14,15-α-epoxytabersonine (lochnericine) found in Catharanthus roseus (Madagascar periwinkle) roots. The pseudovincadifformine 18-hydroxylase is the first CYP identified to modify a pseudoaspidosperma skeleton. Additionally, we demonstrate that the enzyme responsible for C10-hydroxylation of the iboga MIA coronaridine also catalyzes C10-hydroxylation of voaphylline, which bears a quebrachamine skeleton. With the discovery of a new MIA, 11-hydroxypseudovincadifformine, this study provides a comprehensive understanding of MIA biosynthesis and diversification in T. litoralis, highlighting its potential for further exploration.

Cobalt Incorporation Promotes CO2 Desorption from Nickel Active Sites Encapsulated by Nitrogen-Doped Carbon Nanotubes in Urea-Assisted Water Electrolysis.

The potential application prospects of urea-assisted water electrolysis toward hydrogen production in renewable energy infrastructure can effectively alleviate energy shortages and environmental pollution caused by rich urea wastewater. It is of prominent significance that adjusting the CO2 desorption of nickel-based electrocatalysts can overcome the slow reaction kinetics for urea oxidation reaction (UOR) to achieve exceptional catalytic activity. In this work, cobalt (Co) metal doping is employed to boost the UOR performance of nitrogen-doped carbon nanotubes encapsulating nickel nanoparticle electrocatalysts (Ni@N-CNT). The influence of diverse Co doping concentrations on the performance of UOR and hydrogen evolution reaction (HER) catalytic activities associated with stability are systematically investigated. The Co dopant can effectively promote the dynamical conversion of Ni to Ni3+ species; as a result, the UOR catalytic activity is improved by 1.8-fold at 1.6 V vs RHE. The DFT calculation results show that the CoNi bimetallic structure possesses a comparably lower binding energy for CO2 adsorption accelerating the rate-limiting step. Meanwhile, the Co dopant also boosts the HER performance, achieving a 57 mV reduction in overpotential at 100 mA cm-2 due to the creation of more active sites. In addition, the assembled urea-assisted water electrolysis attains 10 mA cm-2 at merely 1.51 V as well as excellent stability.

Importance of additional aliphatic structures generated from in-situ oxidation in development of extra pores in activation of spring jasmine wood

Aliphatic organics are reactive components of biomass in activation, playing important roles in pore development. They could be consumed with progress of activation while introducing external O2 might create additional aliphatic structures via oxidation, probably facilitating generation of extra pores in resulting activated carbon (AC). This was investigated herein by activation of spring jasmine wood with ZnCl2 or K2C2O4 in presence of 11 % or 5 % O2 at 550 or 700 °C. The results suggested that the oxygen added diminished yield of ACO2ZnCl2 by 21.7 % and yield of ACO2K2C2O4 by 29.0 %, resulting from partial oxidation of carbonaceous organics on nascent AC. Nonetheless, O2 presence promoted pore development, increasing SBET from 1833.8 m2g-1 for ACN2-ZnCl2 to 2018.2 m2g-1 for ACO2ZnCl2. The SBET of ACO2K2C2O4 also increased by 35.6 % with presence of O2. Oxidization of nascent AC generated more oxygen-containing species that actively involved in polymerization with ZnCl2 or cracking with K2C2O4 to form more pores. Additionally, O2 presence generated smaller pores in ACO2ZnCl2 while larger ones in ACO2-K2C2O4, enhancing the latter AC for adsorption. Oxidation reactions could also form the AC with oxygen-rice surface and hydrophilic nature, which negatively affect aromatization and reduced interplanar spacing of carbon crystals in AC.

Construction of bifunctional MOF-based composite electrocatalysts promoting oxygen evolution reaction and glucose oxidation reaction and its kinetic deciphering

The climate crisis and the need for green and sustainable energy drive the rapid development of hydrogen production from water electrolysis. Improvements in the kinetics of the anode reaction, which governs the efficiency of water electrolysis, are essential for efficient hydrogen production and key to effectively addressing global environmental and energy challenges. Hence, we focus on improving the kinetics of the anode oxidation reaction. The multi-walled carbon nanotubes coupled with bimetallic organic framework (CoFe-MOF-74) composite electrocatalysts (CoFe-MOF-74@MWCNT) were fabricated for OER and the kinetically more favorable glucose oxidation reaction (GOR). Compared to commercial RuO2, CoFe-MOF-74@MWCNT showed superior OER catalytic performance, exhibiting a lower overpotential (273 mV) and a lower Tafel slope (55 mV dec−1) at a current density of 10 mA cm−2. Moreover, after adding glucose to the anode, the potential required of 10 mA cm−2 was only 1.291 V (vs. RHE), a reduction of 212 mV compared to the OER potential. This reduction in potential demonstrates the efficiency of our catalysts and signifies significant energy savings. The characterization results and theoretical calculations indicated that the superior OER/GOR performance of CoFe-MOF-74@MWCNT can be ascribed to the synergistic effect between MWCNT and the mixed metal nodes of the bimetallic organic framework. The doping of MWCNT promoted the catalyst charge transfer efficiency (Rct was only 5.56 Ω) in the OER process. The mixed metal nodes of CoFe-MOF-74@MWCNT provided more active sites for the electrocatalytic reaction, and promoted the bond-breaking of critical intermediates in the oxidation process, significantly reducing the free energy of catalytic intermediates and accelerating reaction kinetics. This work provides a strategy for designing multifunctional electrocatalysts for OER and biomass small molecule oxidation and highlights the potential for significant energy savings in practical applications.

Selective hydroxylation of benzene via enhanced generation and utilization of hydroxyl radicals with CuZnSbO photocatalyst

Photocatalytic selective benzene hydroxylation via activation of C(sp2)–H under visible light remains a challenging reaction. Copper-incorporated mixed metal oxide photocatalysts have shown promise in addressing this difficulty by enabling visible light harvesting, controlled reactive oxygen species (ROS) generation, effective ROS utilization, and reactant adsorption. However, copper incorporated metal oxide catalysts were suffered from poor catalytic activity and selectivity due to leaching of Cu species. To solve this problem, herein, a novel stable mixed metal oxide (CuZnSbO) was prepared for the first time by applying a facile method. Copper introduction brought about the suitable band gap energy for a wide range of visible light harvesting of the CuZnSbO catalyst. The copper species play a key role in activating H2O2 to produce hydroxyl radicals (•OH) for benzene oxidation by controlling charge recombination. The mixed metal oxide of zinc and antimony supports the included copper strongly enabling copper stability. The CuZnSbO not only generates available hydroxyl radicals but also facilitates efficient hydroxyl radical consumption to initiate C(sp2)–H activation, forming benzene radical intermediates en route to phenol. That is ever reported. CuZnSbO delivered 31.51 % benzene conversion and 100 % phenol selectivity. This work demonstrates the promise of engineered mixed metal oxide that boosts Cu species utilization for H2O2 and benzene activation. The photocatalyst showed good activity in selective oxidative hydroxylation reactions through harnessing visible light and controlled ROS generation. Importantly, Cu cations govern the photocatalytic •OH generation mechanisms as shown by XPS and active site deactivation analysis.

Study on the enhancement of oxidation activity of heated coal in closed fire area and mechanism of reignition by opening seal

Residual heat following the closure of a coal mine fire area induces alterations in the physical and chemical structure of coal, which not only interfere with the opening time but also engenders potential catastrophic incidents upon the reopening of the fire area. Therefore, the structural changes in coal before and after pyrolysis were first analyzed by SEM, BET, XPS, 13C NMR and ESR. Second, the crossing-point temperature and constant-temperature differential heat methods were employed to investigate the process and characteristics of alkyl radical oxidation heat production. Quantum chemistry was integrated to analyze the mechanism of coal oxidation activity enhancement when the fire area was unsealed. The experimental results revealed that the residual heat could induce physicochemical structural changes in coal at varying distances. Upon exposure to oxygen, cracks facilitate oxygen migration and water evaporation mitigates heat consumption. The low-energy barrier of the alkyl radical oxidation reactions intensifies the oxidation activity of pyrolyzed coal, which can react with oxygen at room temperature to release heat. Under heat storage conditions, the active groups in coal are stimulated to further react. As a corollary, the substantial release of heat occurs, heightening the risk of coal re-ignition upon reopening of the fire area. The research results are helpful in performing accurate targeted treatment for different temperature gradients in underground fire areas to prevent the reignition of heated coal in closed fire areas.

Fluorescent/Circular Dichroic Dual-Mode Chiral Upconversion Nanocomposite for Diagnosis and Treatment of Rheumatoid Arthritis.

Chiral nanophotonic materials have emerged as ideal candidates for biosensing applications due to their exceptional sensitivity. However, the inability to directly visualize chiral signals limits their broader application, particularly in disease diagnosis and treatment. In this study, we introduce a chiral nanocomposite based on upconversion nanoparticles (UCNPs), denoted UCNPs@L-POM, that exhibits both upconversion luminescence (UCL) and circular dichroism (CD) signals. This dual-signal system enables ultrasensitive detection and in vivo imaging of ·OH. The detection limits for UCL and CD signals in aqueous solution are 6.258 and 0.912 μM, respectively. This dual-mode sensing approach is also effective at the cellular level. As a demonstration, UCNPs@L-POM enables in situ imaging diagnosis of rheumatoid arthritis (RA), characterized by elevated levels of ·OH expression. Additionally, through the oxidation reaction induced by ·OH, UCNPs@L-POM effectively alleviates paw inflammation and promotes the healing of RA. This work offers new prospects for biological applications of chiral nanocomposites.

Screened d-p Orbital Hybridization in Turing Structure of Confined Nickel for Sulfion Oxidation Accelerated Hydrogen Production.

The sulfion oxidation reaction (SOR) could offer an energy-efficient and tech-economically favorable alternative to the oxygen evolution reaction (OER) for H2 production. Transition metal (TM) based catalysts have been considered promising candidates for SOR but suffer from limited activity due to the excessive bond strength from TM-S2- d-p orbit coupling. Herein, we propose a feasible strategy of screening direct d-p orbit hybridization between TM and S2- by constructing the Turing structure composed of lamellar stacking carbon-confined nickel nanosheets. The optimized p-p orbit coupling between electron-injected carbon and S2- enables exceptional catalytic activity and stability for sulfion degradation and energy-efficient yet value-added H2 production. Specifically, it achieves a current density of 500 mA cm-2 at an ultralow potential of 0.67 V vs. RHE for alkaline SOR. Theoretical calculations indicate that the electron transfer from Ni imparts metallicity and a higher p-band center to carbon shells, thereby contributing to optimized p-p orbit hybridization and a thermodynamically favorable stepwise sulfion degradation. Practically, a two-electrode flow cell achieves an industrial current density of 1 Acm-2 at an unprecedented low voltage of 0.91 V while maintaining stability for over 300 hours, and exhibits high productivities of 3.83 and 0.32 kgh-1m-2 for sulfur and H2, respectively.

Surface Selenium Coating Promotes Selective Methanol-to-Formate Electrooxidation on Ni3Se4 Nanoparticles.

In the quest to replace fossil fuels and reduce carbon dioxide emissions, developing energy technologies based on clean catalytic processes is fundamental. However, the cost-effectiveness of these technologies strongly relies on the availability of efficient catalysts made of abundant elements. Herein, this study presents a one-step hydrothermal method to obtain a series of Ni3Se4 nanoparticles with a layer of amorphous selenium on their surface. When employed as electrocatalysts for the methanol oxidation reaction (MOR), the optimized proper surface Se-coated Ni3Se4 nanoparticles exhibit a high current density of 160 mA cm-2 at 1.6 V, achieving a high methanol-to-formate Faradaic efficiency above 97.8% and excellent stability with less than 20% current decay after an 18 h chronoamperometry test. This excellent performance is rationalized using density functional theory calculations, which unveil that the electrochemical recombination of SeOx results in a reduction of the energy barrier for the dehydrogenation of methanol during the MOR process.

Deep reconstruction of crystalline-amorphous heterojunction electrocatalysts for efficient and stable water and methanol electrolysis.

During electrocatalytic water splitting, surface reconstruction often occurs to generate truly active species for catalytic reactions, but the stability and mass activity of the catalysts is a huge challenge. A method that combines cation doping with morphology control strategies and constructs an amorphous-crystalline heterostructure is proposed to achieve deep reconstruction of the catalyst during the electrochemical activation process, thereby significantly improving catalytic activity and stability. Amorphous iron borate (FeBO) is deposited on cobalt-doped nickel sulfide (Co-Ni3S2) crystals to form ultrathin nanosheet heterostructures (FeBO/Co-Ni3S2) as bifunctional electrocatalysts for the OER and methanol oxidation reaction (MOR). During the OER process, FeBO/Co-Ni3S2 is deeply reconstructed to form a NiFeOOH/Co-Ni3S2 composite structure with ultrathin nanosheets with abundant amorphous-crystalline interfaces to ensure structural stability. Furthermore, Co-Ni3S2 electrocatalysts were synthesized via nickel foam (NF) self-derivation, which resulted in strong adhesion between the catalyst and substrate and formed a hierarchical structure consisting of interconnected nanosheets with excellent mass transfer and abundant active sites to increase the activity and stability of the electrocatalyst. The dual-electrode electrolyzer requires cell voltages of 1.58 and 1.44 V to achieve water and methanol overall electrolysis at a current density of 10 mA cm-2 and keep working over 100 and 25 h, respectively. This strategy provides a new way to promote reconstruction to construct excellent bifunctional electrocatalysts.

The first application of high-order Virial equation of state and ab initio multi-body potentials in modeling supercritical oxidation in jet-stirred reactors

Supercritical oxidation processes in jet-stirred reactors (JSR) have been modeled based on ideal gas assumption. This can lead to significant errors in or complete misinterpretation of modeling results. Therefore, this study newly developed a framework to model supercritical oxidation in JSRs by incorporating ab initio multi-body molecular potentials and high-order mixture Virial equation of state (EoS) into real-fluid conservation laws, with the related numerical strategies highlighted. With comparisons with the simulation results based on ideal EoS and the experimental data from high-pressure JSR experiments, the framework is proved to be a step forward compared to the existing JSR modeling frameworks. To reveal the real-fluid effects on the oxidation characteristics in jet-stirred reactors, simulations are further conducted at a wide range of conditions (i.e., temperatures from 500 to 1100 K and pressures from 100 to 1000 bar). The real-fluid effect is found to significantly promote fuel oxidation reactivity, especially at low temperatures, high pressures, and for mixtures with heavy fuels. The significant influences of real-fluid behaviors on JSR oxidation characteristics emphasize the need to adequately incorporate these effects for future modeling studies in JSR at high pressures, which has now been enabled through the framework proposed in this study.

Interfacial and electronic dual regulation of metal organic frameworks for enhanced catalytic oxidation of peroxymonosulfate into dyes

In heterogeneous advanced oxidation processes, it is important to improve the catalytic performance, which can be achieved by increasing the mass transfer of catalysts and utilization efficiency of reactive oxygen species (ROSs). Herein, the functional groups, amino group (NH2) and hydroxyl group (OH), were introduced onto the surface of metal organic frameworks (MOFs), FeBDC (Iron terephthalate) by ligand exchange. The synthesized MOFs were used as catalysts to activate peroxymonosulfate (PMS) for the efficient removal of dye from wastewater. The NH2/-OH groups accumulated at the surface of MOFs to significantly enhanced their hydrophilicity, which favored dye adsorption efficiency on the surface of MOFs from aqueous solution. This dye enrichment was benefited to the high utilization of ROSs due to the shorter transfer distance in solution. Additionally, the introduction of NH2/OH favored the reduction in electrochemical resistance both within the bulk and at the interface of the MOFs, thereby facilitating the electron transfer from the MOFs to PMS. The efficient utilization of ROSs (the radicals (SO4− and O2−) and non-radical (1O2)) generated by PMS removed nearly all RB171 (96.2–98.5 %) by oxidation reaction. The azo bonds and aromatic rings of dye molecules were susceptible to the attack by these ROSs. At the utilization of 5 cycles, iron leaching from MOFs/PMS was very low, satisfying the value of discharge standards. This work demonstrates that the functional groups presented in MOFs effectively facilitate the dual regulation of dye enrichment and catalytic activity in heterogeneous advanced oxidation processes.

Insight Into Intermediate Behaviors and Design Strategies of Platinum Group Metal-Based Alkaline Hydrogen Oxidation Catalysts.

Hydrogen oxidation reaction (HOR) can effectively convert the hydrogen energy through the hydrogen fuel cells, which plays an increasingly important role in the renewable hydrogen cycle. Nevertheless, when the electrolyte pH changes from acid to base, even with platinum group metal (PGM) catalysts, the HOR kinetics declines with several orders of magnitude. More critically, the pivotal role of reaction intermediates and interfacial environment during intermediate behaviors on alkaline HOR remains controversial. Therefore, exploring the exceptional PGM-based alkaline HOR electrocatalysts and identifying the reaction mechanism are indispensable for promoting the commercial development of hydrogen fuel cells. Consequently, the fundamental understanding of the HOR mechanism is first introduced, with emphases on the adsorption/desorption process of distinct reactive intermediates and the interfacial structure during catalytic process. Subsequently, with the guidance of reaction mechanism, the latest advances in the rational design of advanced PGM-based (Pt, Pd, Ir, Ru, Rh-based) alkaline HOR catalysts are discussed, focusing on the correlation between the intermediate behaviors and the electrocatalytic performance. Finally, given that the challenges standing in the development of the alkaline HOR, the prospect for the rational catalysts design and thorough mechanism investigation towards alkaline HOR are emphatically proposed.

High-Entropy PdRhFeCoMo Metallene With High C1 Selectivity and Anti-Poisoning Ability for Ethanol Electrooxidation.

The urgent demand for designing highly efficient electrocatalysts for ethanol oxidation reaction (EOR) with elevated C1 selectivity, robust anti-poisoning capability, and high mass activity presents a formidable challenge. Herein, a novel two-dimentional (2D) high-entropy PdRhFeCoMo metallene (PdRhFeCoMo HEM) electrocatalyst is successfully synthesized via a mild one-step solvothermal method. The PdRhFeCoMo HEM, characterized by intentionally designed multi-metallic ensembles and ultra-thin graphene-like structures, delivers an impressive mass activity of 7.47 A mgPd+Rh -1 and specific activity of 25.5mA cm-2. Furthermore, it can retain a mass activity of 0.56 A mgPd+Rh -1 after undergoing 20000 s of continuous testing, demonstrating outstanding resistance to poisoning. More significantly, the PdRhFeCoMo HEM demonstrates an elevated capacity for C─C bond cleavage with a superior C1 selectivity of up to 84.12%. In situ spectroscopy analysis, combined with theoretical calculations, reveals that the deliberate design of components and structures effectively regulate the electronic properties of the Pd site, thereby enhancing the adsorption of reactant and reducing the reaction barrier of the C1 pathway. Finally, a flexible solid-state ethanol fuel cell assembled by PdRhFeCoMo HEM presents a maximum power density of 20.1mW cm-2 and can operate continuously by repeatedly adding ethanol fuel.

Understanding the Negative Apparent Activation Energy for Cu2O and CoO Oxidation Kinetics at High Temperature near Equilibrium

The pairs of Cu2O/CuO and CoO/Co3O4 as the carriers of transferring oxygen and storing heat are essential for the recently emerged high-temperature thermochemical energy storage (TCES) system. Reported research results of Cu2O and CoO oxidation kinetics show that the reaction rate near equilibrium decreases with the temperature, which leads to the negative activation energy obtained using the Arrhenius equation and apparent kinetics models. This study develops a first-principle-based theoretical model to analyze the Cu2O and CoO oxidation kinetics. In this model, the density functional theory (DFT) is adopted to determine the reaction pathways and to obtain the energy barriers of elementary reactions; then, the DFT results are introduced into the transition state theory (TST) to calculate the reaction rate constants; finally, a rate equation is developed to describe both the surface elemental reactions and the lattice oxygen concentration in a grain. The reaction mechanism obtained from DFT and kinetic rate constants obtained from TST are directly implemented into the rate equation to predict the oxidation kinetics of Cu2O without fitting experimental data. The accuracy of the developed theory is validated by experimental data obtained from the thermogravimetric analyzer (TGA). Comparing the developed theory with the traditional apparent models, the reasons why the latter cannot appropriately predict the true oxidation characteristics are explained. The reaction rate is jointly controlled by thermodynamics (reaction driving force) and kinetics (reaction rate constant). Without considering the effect of the reaction driving force, the negative apparent activation energy of Cu2O oxidation is obtained. However, for CoO oxidation, the negative apparent activation energy is still obtained although the effect of the reaction driving force is considered. According to the DFT results, the activation energy of the overall CoO oxidation reaction is negative, but the energy barriers of the elementary reactions are positive. Moreover, according to the first-principle-based rate equation theory, the pre-exponential factor in the kinetic model is dependent on the partition function ratio and decreases with the temperature for the Cu2O and CoO oxidation near equilibrium, which results in the apparent activation energy being slightly lower than the actual value.

Heteroatom Engineering in Earth-Abundant Cobalt Electrocatalyst for Energy-Saving Hydrogen Evolution Coupling with Urea Oxidation.

The development of multifunctional electrocatalysts with high performance for electrocatalyzing urea oxidation-assisted water splitting is of great significance for energy-saving hydrogen production. In this work, we demonstrate a novel heteroatom engineering strategy for development of B-doped Co as a multifunctional electrocatalyst for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and urea oxidation reaction (UOR). Density functional theory (DFT) results suggest that a B dopant can efficiently adjust the electron reconstruction of the exposure of Co sites nearby and facilitate electron transfer, resulting in an optimal d-band center along with a lower Gibbs free energy barrier. Ultimately, the obtained B-Co exhibits pH-universal HER properties in various electrolytes. A highly efficient HER performance with overpotentials as low as 27, 163, and 430 mV to -10, -100, and -500 mA cm-2 in 1.0 M KOH, respectively, is observed for the B-Co electrode. More importantly, the UOR-assisted electrolyzer only requires a voltage input of 1.55 V to produce the current densities of 50 mA cm-2, resulting in a 200 mV saving-energy potential compared to water electrolysis, demonstrating its high efficiency of hydrogen production in industrial applications.