Oxidation Reaction Research Articles

Supported bimetallic Pt-Pd/ZrVFeTi catalyst for H2 oxidation and its enhanced catalytic hydrogen elimination performance

The deflagration of hydrogen in confined spaces is a significant safety concern. To eliminate hydrogen for ensuring safety, we study catalysts for catalytic oxidation of hydrogen at room temperature. Bimetallic PtPd catalyst is prepared on the hydrogen storage alloy ZrVFeTi by the chemical reduction method. The structure, composition, morphology and elemental analyses are characterized using XRD, HR-TEM, XPS and ICP-AES, and its hydrogen elimination performance is also studied. The obtained results show that Pt-Pd/ZrVFeTi bimetallic catalyst displays superior catalytic performance toward H2 oxidation reaction than monometallic Pt/ZrVFeTi or Pd/ZrVFeTi catalyst, which can be attributed to the presence of the PtPd alloyed structures. The Pt-Pd/ZrVFeTi bimetallic catalyst exhibits a high hydrogen conversion of 98.8 % when the hydrogen inlet concentration is 4 vol%, which is higher than 94.3 % for Pd/ZrVFeTi and 91.3 % for Pt/ZrVFeTi. Furthermore, it maintains excellent catalytic activity over 120 mins of the testing experiments, demonstrating remarkable stability. The synergistic effect between Pt and Pd proves beneficial for H2 oxidation reaction.

μ-nitrido diiron phthalocyanines: Electron-withdrawing vs electron-donating substituent effect on oxidation reaction catalysis

μ-nitrido diiron phthalocyanines: Electron-withdrawing vs electron-donating substituent effect on oxidation reaction catalysis

Electron Delocalized Ni Active Sites in Spinel Catalysts Enable Efficient Urea Oxidation

The urea oxidation reaction (UOR) has attracted much attention as an efficient alternative reaction to oxygen evolution reaction (OER) due to its low required overpotential. Despite significant progress in efficient nickel‐based catalysts, the fundamental issues regarding product selectivity control and dissociation mechanism during the UOR process have not been clarified. Here, we report that tuning the electron delocalization strength of Ni sites significantly affects the OH‐ binding sites, altering urea molecule dissociation patterns in alkaline systems. Using spinel NiCo2O4 as a model catalyst, the charge delocalization strength of nickel active centers is influenced by the degree of phosphorus‐substituted anions. Specifically, complete phosphorus‐substituted spinel enhances N2 selectivity to over 26.8% with a peak current density of 300 mA·cm‐2, while partial phosphorus‐substituted spinel achieves a Faraday efficiency of 78.1% for liquid products (NOx‐). Experiments and theory reveal that strong charge delocalization at Ni sites favors remote‐site attack on urea molecules by hydroxide ions, whereas weak delocalization prefers nearby‐site attack, enhancing UOR efficiency and suppressing OER in both pathways.

Cu Anchored Carbon Nitride (Cu/CN) Catalyzes Selective Oxidation of Thiol by Controlling Reactive Oxygen Species Generation.

Production of H2O2 using heterogeneous semiconductor photocatalysts has emerged as an ecofriendly and practical approach across various applications, ranging from environmental detoxification to fuel cells and chemical synthesis. Extensive efforts have been devoted to engineering semiconductors to enhance their catalytic capabilities for H2O2 production. However, in chemical synthesis, the utilization of the potent oxidant H2O2 can present challenges in selectively oxidizing organic compounds. In this study, we introduce copper atoms into carbon nitride (Cu/CN), facilitating the generation of hydroperoxyl radicals (·OOH) as primary reactive oxidants and offering reaction conditions entirely devoid of H2O2 via the Fenton reaction. Cu/CN demonstrates selective oxidation of thiols to disulfides, in contrast to other current heterogeneous photocatalysts that yield undesired overoxidized side products, such as thiosulfinate and thiosulfonate. Cu/CN's controllable capacity for specific ROS generation, broad substrate scopes, and recyclability empower greener and highly selective photooxidation of organic compounds.

Two‐Electron Oxidative Atom and Group Transfer Reactions at a Well‐Defined Uranium(II) Center

The multi‐electron redox chemistry of uranium(II) compounds remains largely unexplored. Herein, we report a series of two‐electron oxidative atom and group transfer reactions at a well‐defined uranium(II) center. The reactions of uranium(II) complexes [M][(AdTPBN3)U] (M = K(2,2,2‐cryptand) and K(18‐crown‐6)(THF)) with pyridine‐N‐oxide or nitrosobenzene, elemental sulfur/selenium or triphenylphosphine sulfide/selenide, and ditellurium salt led to the isolation of uranium(IV) terminal oxo and chalcogenido complexes [M][(AdTPBN3)UX] (X = O, S, Se, Te). In addition, the reactions of [M][(AdTPBN3)U] with aryl azides ArN3 or diazoalkanes R2CN2 quantitatively yielded uranium(IV) terminal imido [M][(AdTPBN3)UNAr] or hydrazonido(2–) complexes [M][(AdTPBN3)UN2CR2], respectively. Notably, the low‐temperature reaction between [M][(AdTPBN3)U] and mesityl azide allowed the isolation of the first uranium(IV) aryldiazenylimido complex as an intermediate. These uranium(IV)–element multiply bound compounds were fully characterized by X‐ray crystallography, 1H NMR spectroscopy, absorption spectroscopy, solution magnetic susceptibility, and elemental analysis. The controlled two‐electron oxidative reactions at a uranium(II) center not only expand the redox reactivity of uranium(II) but also offer a convenient new route to access uranium–element multiply bound compounds.

Two-Electron Oxidative Atom and Group Transfer Reactions at a Well-Defined Uranium(II) Center.

The multi-electron redox chemistry of uranium(II) compounds remains largely unexplored. Herein, we report a series of two-electron oxidative atom and group transfer reactions at a well-defined uranium(II) center. The reactions of uranium(II) complexes [M][(AdTPBN3)U] (M = K(2,2,2-cryptand) and K(18-crown-6)(THF)) with pyridine-N-oxide or nitrosobenzene, elemental sulfur/selenium or triphenylphosphine sulfide/selenide, and ditellurium salt led to the isolation of uranium(IV) terminal oxo and chalcogenido complexes [M][(AdTPBN3)UX] (X = O, S, Se, Te). In addition, the reactions of [M][(AdTPBN3)U] with aryl azides ArN3 or diazoalkanes R2CN2 quantitatively yielded uranium(IV) terminal imido [M][(AdTPBN3)UNAr] or hydrazonido(2-) complexes [M][(AdTPBN3)UN2CR2], respectively. Notably, the low-temperature reaction between [M][(AdTPBN3)U] and mesityl azide allowed the isolation of the first uranium(IV) aryldiazenylimido complex as an intermediate. These uranium(IV)-element multiply bound compounds were fully characterized by X-ray crystallography, 1H NMR spectroscopy, absorption spectroscopy, solution magnetic susceptibility, and elemental analysis. The controlled two-electron oxidative reactions at a uranium(II) center not only expand the redox reactivity of uranium(II) but also offer a convenient new route to access uranium-element multiply bound compounds.

Regulating socketed geometry of nanoparticles on perovskite oxide supports for enhanced stability in oxidation reactions.

Heterogeneous catalysts with highly dispersed active particles on supports often face stability challenges during high-temperature industrial applications. The ex-solution strategy, which involves in situ extrusion of metals to form socketed particles, shows potential for addressing this stability issue. However, a deeper understanding of the relationship between the socketed geometry of these partially embedded nanoparticles and their catalytic performance is still lacking. Here, in situ transmission electron microscopy and theoretical calculations are utilized to investigate the oxygen-induced ex-solution process of Pd-doped LaAlO3 with varying concentrations of La vacancies (LaxAl0.9Pd0.1O3-δ). We find that the socketed geometry of Pd-based particles can be tuned by manipulating the levels of La deficiencies in the oxide support, which in turn influences the catalytic performance in high-temperature oxidation reactions. As for the socketed particles, the balance between particle size and outcrop height is crucial for determining the oxidation activity and sinter-resistance behavior. Consequently, the optimized catalyst, La0.8Al0.9Pd0.1O3-δ, exhibits superior catalytic performances, particularly high stability (still working after aging at 1000 °C for 50 h) and water resistance in various combustion reactions (e.g., CH4 oxidation and C3H8 oxidation).

Compartmentalized Sesquiterpenoid Biosynthesis and Functionalization in the Chlamydomonas reinhardtii Plastid.

Terpenoids play key roles in cellular metabolism and can have specialized functions. Their heterologous production in microbial hosts offers an alternative to natural extraction. Here, we developed a subcellular engineering approach in the model green alga Chlamydomonas reinhardtii by targeting both sesquiterpenoid synthases and cytochrome P450s (CYPs) to the plastid, exploiting its photosynthetic electron transport chain to drive CYP-mediated oxidation without reductase partners. Nuclear-encoded sesquiterpenoid synthases were expressed with farnesyl pyrophosphate synthase fusions and targeted to the plastid, while CYPs were modified for soluble localization in the plastid stroma by removing transmembrane domains. The plastid environment supported hydroxylation, epoxidation, and oxidation reactions, with functionalization efficiencies reaching 80% of accumulated products. Carbon source availability influenced product ratios, revealing metabolic flexibility in the engineered pathways. Overall sesquiterpenoid yields ranged between 250-2500 µg L-1 under screening conditions, establishing proof-of-concept for using plastid biochemistry in complex terpenoid biosynthesis. Living two-phase terpenoid extractions with different perfluorinated solvents revealed variable performances based on sesquiterpenoid functionalization and solvent type. This work demonstrates that photosynthetic electron transport can drive CYP-mediated functionalization in engineered subcellular compartments. However, improvements in photobioreactor cultivation concepts will be required to facilitate the use of algal chassis for scaled production.

Discovery and characterization of NADH oxidases for selective sustainable synthesis of 5-hydroxymethylfuran carboxylic acid

Efficient regeneration of NAD+ remains a significant challenge for oxidative biotransformations. In order to identify enzymes with higher activity and stability, a panel of NADH oxidases (Nox) was investigated in the regeneration of nicotinamide cofactors for the oxidation of hydroxymethyl furfural (HMF) to 5-hydroxymethyl-2-furancarboxylic acid (HMFCA). We present novel Nox that exhibit remarkable catalytic activities, elevated thermal and pH stabilities, and higher intrinsic flavin loadings, thus eliminating the need for external flavin addition. The kinetic analysis of the NADH oxidases indicates that AdNox, GdNox, CmNox, and LvNox exhibit Vmax values of 86 U/mg, 50 U/mg, 4.3 U/mg, and 23 U/mg, respectively. When these NADH oxidases were applied in a HMF oxidation reaction, LvNox demonstrated the highest HMFCA yield of 97 % in the presence of 0.1 mM NAD and 10 mM HMF. In contrast to previously reported NADH oxidases from the same family, these NADH oxidases naturally accept NADPH as a substrate. Rapid kinetics experiments identified the oxidative reaction as the rate-limiting step of the reaction. NADH oxidases achieved high atom economy, a high reaction mass efficiency and a low process mass intensity. The findings contribute significantly to the field of biocatalysis and offer potential avenues for more environmentally friendly cofactor regeneration in chemical synthesis.

Metal-Organic Framework-Templated Synthesis of Nickel-Alumina Nanocatalysts Improves Catalyst-Support Interaction for Higher Activity and Stability in Biogas Reforming under Controlled Oxidizing Conditions.

Tri-reforming methane with CO2, O2, and H2O mixtures requires a delicate balance of dry-reforming, partial oxidation, and steam-reforming reactions to improve the CO2 conversion and H2/CO ratio. Nickel-alumina has been reported before for the tri-reforming of methane, although at higher temperatures (>900 °C). This is because the current approaches for nickel-alumina synthesis are ineffective in generating stronger catalyst-support interactions necessary to maintain higher active sites and stall carbon nanotube (CNT) deposition. Here, we report a synthesis method that allows controlled loading of nickel on alumina-based MIL-53 metal-organic framework followed by calcination to generate 2.5-10 wt % nickel nanoparticles dispersed on alumina. The 5 wt % nickel-alumina mixtures resulted in nanometer-sized crystallites, better metal dispersion, and more active sites for enhanced catalytic activity. This optimal loading of nickel allows stronger interaction with alumina for over 100 h of stable performance of tri-reforming at 800 °C, achieving ∼98% CH4 conversion, ∼36% CO2 conversion, and no carbon deposition while producing Fischer-Tropsch-ready feed containing a H2/CO ratio of 3.2.

Atomic behaviors in PdRu solid-solution nanoparticles on CeO2-ZrO2 support for the three-way catalytic reaction

Understanding the behavior of noble-metal catalysts is a key point of catalysis research aimed at reducing the environmental and economic costs associated with the increased use of automobiles. In this study, the atomic-behaviors of Ru and Pd atoms in PdRu solid-solution nanoparticles (NPs) supported on CeO2-ZrO2 (CZ) as a Rh-free three-way catalyst in a modeled three-way catalytic reaction (TWCR) were elucidated using a gas conversion analysis, transmission electron microscopy, and in-situ X-ray absorption fine structure spectroscopy. We found that the PdRu NPs enlarged by the annealing effect separated a smaller grain size with the Pd-rich and Ru-rich phase under TWCR. Most of the oxidation and reduction reactions under the modeled TWCR occurred on the Ru. However, the Pd metals acted as a major role of the reduction of NO gas and oxidation of CO and C3H6 gas. Ru atoms just is a minor role during the modeled TWCR. This study demonstrates the potential of PdRu NPs as a three-way catalyst and reveals the atomic-behavior and catalytic role under the modeled TWCR.

Hollow Pt‐Encrusted RuCu Nanocages Optimizing OH Adsorption for Efficient Hydrogen Oxidation Electrocatalysis

As one of the best candidates for hydrogen oxidation reaction (HOR), ruthenium (Ru) has attracted significant attention for anion exchange membrane fuel cells (AEMFCs), although it suffers from sluggish kinetics under alkaline conditions due to its strong hydroxide affinity. In this work, we develop ternary hollow nanocages with Pt epitaxy on RuCu (Pt‐RuCu NCs) as efficient HOR catalysts for application in AEMFCs. Experimental characterizations and theoretical calculations confirm that the synergy in optimized Pt8.7‐RuCu NCs significantly modifies the electronic structure and coordination environment of Ru, thereby balancing the binding strengths of H* and OH* species, which leads to a markedly enhanced HOR performance. Specifically, the optimized Pt8.7‐RuCu NCs/C achieves a mass activity of 5.91 A mgPt+Ru‐1, which is ~3.3, ~2.2, and ~15.0 times higher than that of RuCu NCs/C (1.38 A mgRu‐1), PtRu/C (1.83 A mgPt+Ru‐1) and Pt/C (0.37 A mgPt‐1), respectively. Impressively, the specific peak power density of fuel cells reaches 15.9 W mgPt+Ru‐1, significantly higher than those of most reported PtRu‐based fuel cells.

Investigation of the microstructure, high temperature oxidation and deformation behavior of Hastelloy X superalloy fabricated by ultrasonic vibration laser directed energy deposition

In this paper, the effect of ultrasonic vibration on the microstructure and high-temperature properties of Hastelloy X fabricated by laser directed energy deposition (LDED) was investigated. With applying ultrasonic vibration, the superalloy grains were significantly refined from 72.23μm to 44.92μm, and the fiber texture was transformed from <100>//z (building direction, BD) to <111>//z (BD). There was almost no effect on the phase composition of the superalloy. In addition, with applying ultrasonic vibration, the oxidation weight gain of LDED Hastelloy X high temperature oxidation sample was lower, and the oxidation rate constant k value decreased from 0.6416 to 0.5108, which was reduced by 20.38 %. The samples without and with the application of ultrasonic vibration generated a continuous oxide film, which hindered the further occurrence of the oxidation reaction. The thickness of the oxide film decreased from 6.47μm to 4.89μm, a decrease of 24 %. The oxide film was mainly composed of two parts. The surface was composed of Cr2O3 and spinel oxides FeCr2O4, NiFe2O4 and NiCr2O4, and the part near the substrate was a single Cr2O3 oxide. With applying ultrasonic vibration, the phase composition of the oxide film surface did not change much, but the proportion of single Cr2O3 oxide inside was higher, which had better high temperature oxidation resistance. With applying ultrasonic vibration, the peak stress of high temperature deformation of LDED Hastelloy X specimen increased from 364.1 MPa to 410.7 MPa, with an increase of 12 %. The high temperature deformation resistance of LDED Hastelloy X was enhanced with ultrasonic vibration.

Atomic mechanisms of oxidative behavior of ferrochromium alloys by water-oxygen environment

The formation of chromium-rich oxide layers on the surface of Fe-Cr alloys significantly impacts their performance at elevated temperatures. Understanding the formation process of these oxide layers at the atomic scale is crucial for further elucidating oxidation behavior, though it presents substantial challenges. In this study, ReaxFF molecular dynamics simulations were used to investigate the oxidation behavior of Fe-Cr alloys in high temperature water vapor and oxygen environments. The results demonstrate that chromium atoms are the primary contributors to the oxidation process, with Cr atoms diffusing to the surface more readily than iron atoms, leading to uneven stress distribution and creating high-stress regions near the Cr atoms. Additionally, hydrogen atoms generated from the breakdown of water molecules infiltrate the alloy matrix, promoting the creation, movement, and clustering of cation and anion vacancies, thereby enhancing oxidation reactions in high-temperature, humid conditions. The study further analyzes electron transfer during single-atom chemical reactions and explores the linear relationship between varying Cr content (10 %–30 %) and oxidation behavior under identical environmental conditions. These findings provide an important theoretical basis for optimizing the performance of Fe-Cr alloys for applications in high temperature environments.

Oxygen nonstoichiometry, defect chemistry and thermodynamic modeling of donor-doped CaMnO3−δ: Effect of disproportionation of Mn3+ ions in nonstoichiometric manganites

The present study concerns the investigation of the oxygen content in the perovskite-type manganite Ca0.6−уSr0.4HoуMnO3−δ (0 ≤ y ≤ 0.15) as a function of temperature (T) and oxygen partial pressure (pO2) in the gas phase since the oxygen nonstoichiometry (δ) has a significant impact on the physicochemical properties of materials applied in a variety of high-temperature devices. The δ value has been determined using thermogravimetry and coulometric titration methods. The resulting pO2 – T – δ diagrams have been accurately described by the defect chemical equilibrium model, that accounts for the oxidation reaction of Mn3+ to Mn4+ in all of the studied samples. Additionally, for the samples containing holmium, the disproportionation reaction of Mn3+ to Mn2+ and Mn4+ has been considered. This is the first study to demonstrate the distinction in Mn3+ disproportionation reactions in stoichiometric and nonstoichiometric Ca0.6−уSr0.4HoуMnO3−δ manganites, resulting from the discrepancy in oxygen coordination of Mn3+ ions at low and high temperatures. The experimental dependencies δ(T, pO2) have been employed in order to calculate the chemical potential of oxygen (ΔμO) in relation to the standard state. Statistical thermodynamic analysis has yielded equations that describe the relationships between the partial molar enthalpy (ΔhO) and entropy (ΔsO) of oxygen with standard enthalpies and entropies of defect formation reactions, Mn3+ ion concentration, and nonstoichiometry δ. The calculated functions ΔhO(y, δ, T) and ΔsO(y, δ, T) have been shown to exhibit a high degree of correlation with the values of ΔhO and ΔsO obtained from the linear dependencies of ΔμO on T.

Highly specific colorimetric detection of sarcosine using surface molecular imprinted Zn/Ce-ZIF

Despite significant progress in nanozyme research and the advancement of analytical techniques, the inherent lack of specificity for target analytes often limits their utility in analysis. Integrating specific recognition capabilities into inorganic nanomaterials, independent of biological catalysts or adaptors, represents a crucial breakthrough in the field. Detecting Sarcosine (Sar) in human urine has recently emerged as a non-invasive biomarker for prostate cancer (PCa), presenting a valuable diagnostic tool. This study introduces a novel method for embedding molecular imprinting sites directly onto the surface of a Zn/Ce-based zeolitic imidazolate framework (Zn/Ce-ZIF) nanozyme, facilitating the development of a highly specific colorimetric assay for precise Sar measurement. By utilizing the lanthanide metal cerium as the catalytic element and ZIF-8 as the structural scaffold, we synthesized spherical Zn/Ce-ZIF nanozymes with exceptional oxidase-like catalytic efficiency. The efficiency of molecular imprinting experiments and the ability of molecularly imprinted polymers (MIPs) to identify target molecules were significantly enhanced by using theortical calculations to screen suitable functional monomers. The molecularly imprinted nanozyme (Zn/Ce-ZIF@MIP) initiates a colorimetric oxidation reaction of 3,3′,5,5′-tetramethylbenzidine (TMB), wherein the presence of Sar facilitates selective recognition and capture by the MIP shell, modulating the colorimetric response by hindering TMB’s access to the catalytic site. An intelligent color extraction detection device has been developed for the rapid perception of Sar. This colorimetric sensing platform has been validated through the detection of Sar in simulated urine samples. Overall, the application of surface molecular imprinting enhances the functionality of nanozymes in analytical fields.

Enhanced co-production of H2 and formic acid via Ni-facilitated Cu+/Cu2+ cycling in an industry-level hybrid water splitting system

Replacing the oxygen evolution reaction (OER) with the glucose oxidation reaction (GOR) to produce formic acid (FA) is a promising development in green hydrogen production. However, at high current densities, competition with the OER reduces the Faradaic efficiency (FE) of the GOR, limiting its practical applicability and compromising safety. In this study, NiO/CuO nanocomposites grown on Ni foam (NiCu-O/NF) were prepared by oxidizing NiCu-OH/NF to produce a GOR electrocatalyst. The incorporation of Cu effectively suppressed the OER. Additionally, Cu2+ in CuO can spontaneously oxidize glucose, generating Cu2O. However, the resulting Cu2O fails to sustain a high-rate GOR. Owing to the higher surface work function of NiO than that of Cu2O, high-valence Ni species facilitated the reconversion of Cu2+, as evidenced by characterization before and after the GOR. The robust Cu+/Cu2+ cycling enhanced the GOR catalytic performance and ensured good catalytic stability over 40 h. A potential pathway was proposed for producing FA by the GOR. A two-electrode electrolyzer assembled with Ni1Cu2-O/NF (anode) and Ni1Cu2-OH/NF (cathode) afforded 100 and 600 mA cm−2 at 1.46 and 1.82 V, respectively, without any OER interference. Furthermore, FA was confirmed to be the primary anodic product, achieving a maximum FE of 92.67 % at 1.3 V.

Revealing efficacy of AgCuFe2O4@GO/MnO2 in 3D electrochemical oxidation for ceftriaxone degradation in aqueous media: Optimization and mechanisms

Ceftriaxone (CEF), a broad-spectrum antibiotic with a long half-life, is extensively used for the curative purposes of many bacterial infections. Nevertheless, given its strong resistance and the inefficiency of traditional techniques in breaking it down and eliminating it, this study assessed the use of a synthesized AgCuFe2O4@GO/MnO2 nanoparticle electrode (NPE) in a three-dimensional electrochemical oxidation reaction (3DER) to remove CEF. The AgCuFe2O4@GO/MnO2 NPE was fabricated by a co-precipitation process aided by a microwave. The physical and chemical structure of the nanocomposite was determined and verified using a range of analytical techniques, such as FESEM, XRD, EDS-mapping, FTIR, BET, VSM, and TGA. These investigations indicated that the NPE had a large specific surface area, a maintained crystal structure, strong magnetic characteristics, and a quasi-spherical morphology. A 3DER with optimal parameters (pH 5, initial CEF concentration 20 mg/L, NPE dose 0.7 g/L, electrode distance 3 cm, 0.12 mM persulfate electrolyte, and 8.5 mA/cm2 current density for 45 minutes) removed 86.8 % of CEF in synthetic samples and 71.3 % in real wastewater samples, with a mineralization rate of 53.4 %, also had 253.2 kWh/g energy consumption. The 3DER matched the pseudo-first-order kinetic and the Langmuir-Hinshelwood model (R2 > 0.9), with KC and KL-H values of 0.954 mg/L.min and 0.032 L/mg. The removal effectiveness of 64.9 % was achieved after five cycles of recovering and regenerating the NPE. The AgCuFe2O4@GO/MnO2 NPE is beneficial for treating a wide range of industrial and hospital wastewaters due to its magnetic characteristics, chemical stability, reusability, and remarkable efficiency.

UNLEASH: Ultralow Nanocluster Loading of Pt via Electro-Acoustic Seasoning of Heterocatalysts.

The shift toward sustainable energy has fueled the development of advanced electrocatalysts to enable green fuel production and chemical synthesis. To date, no material outperforms Pt-group catalysts for key electrocatalytic reactions, necessitating advanced catalysts that minimize use of these rare and expensive constituents (i.e., Pt) to reduce cost without sacrificing activity. Whilst a myriad of routes involving co-synthesis of Pt with other elements have been reported, the Pt is often buried within the bulk of the composite, rendering a large proportion of it inaccessible to the interfacial electrocatalytic reaction. Surface decoration of Pt on arbitrary substrates is therefore desirable to maximize catalytic activity; nevertheless, Pt electrodeposition suffers from clustering and ripening effects that result in large ( ) aggregates that hinder electrocatalytic activity. Herein, an unconventional synthesis method is reported that utilizes high-frequency (10 MHz) acoustic waves to electrochemically 'season' a gold working electrode with an ultralow loading of Pt nanoclusters. The UNLEASH platform is shown to facilitate high-density dispersion of nanometer-order clusters at the bimetallic interface to enable superior atomic utilization of Pt. This is exemplified by its utility for methanol oxidation reaction (MOR), wherein a mass activity of 5.28 A is obtained, outperforming all other Au/Pt bimetallic electrocatalysts reported todate.

Controlling Hydrogen Evolution and CO2 Reduction at Transition Metal Hydrides.

ConspectusFuel-forming reactions such as the hydrogen evolution reaction (HER) and CO2 reduction (CO2R) are vital to transitioning to a carbon-neutral economy. The equivalent oxidation reactions are also important for efficient utilization in fuel cells. Metal hydride intermediates are common in these catalytic and electrocatalytic processes. Guiding metal hydride reactivity is important for achieving selective, kinetically fast, and low overpotential redox reactions. Our work has focused on understanding kinetic and thermodynamic aspects for controlling these reactive hydride species in an effort to design more selective electrocatalysts that operate at low overpotentials. Key to our research approach is understanding the free energy changes and rate of discrete steps of catalysis through the synthesis of proposed intermediates to independently investigate catalytic steps. Hydricity, the free energy of hydride dissociation, and how these values change with metal and ligand environment have informed catalyst design in the past few decades. We describe here how we have advanced upon these earlier studies.In our early studies we sought to understand solvent-dependent changes in hydricity for transition metal hydrides and how they impact the free energy for reduction of CO2 to formate (HCO2-). Additionally, we described how hydricity values can be applied to optimize HER and CO2R catalysis. This framework provides general guidelines for achieving selective CO2 reduction to formate without concomitant generation of H2. Kinetic information on steps in the proposed catalytic cycle of HER and CO2R catalysts were evaluated to identify potential rate-determining steps. As a second approach to achieve selective reduction for CO2, we explored two catalyst design strategies to kinetically inhibit HER using electrostatic (charged) and steric interactions. Hydricity values and other considerations for minimizing the free energy of proposed catalytic steps were also used to design an electrocatalyst for the interconversion between CO2 and HCO2- at low overpotentials. Further, we discuss our efforts to translate the CO2 hydrogenation activity of homogeneous catalysts to electrocatalysis.All of these catalytic systems operate with classical metal hydrides, where the electrons and proton are colocated on the metal center. However, classical metal hydrides all require very reducing potentials to generate sufficiently strong hydride donors for CO2 reduction. An analysis of metal hydride hydricity and reduction potentials shows that the strong correlation between reduction potential and hydricity is a general trend because the former is also highly correlated to pKa. However, formate dehydrogenase (FDH) generates a competent hydride donor at more mild potentials through bidirectional hydride transfer, where the proton and electrons of the hydride are not colocated. This bioinspired approach points to a promising new strategy for generating strong hydride donors at milder potentials and will surely open new avenues for using hydricity as a guide for addressing new and existing problems in catalysis.