Oxidation Of Small Molecules Research Articles

Electrooxidation of glycerol to formic acid coupled with Energy-Saving hydrogen production over ruthenium doped Cobalt-Based nanosheet arrays

The utilization of small molecule oxidation reactions as a substitute for the sluggish oxygen evolution reaction (OER) in traditional water electrolysis represents an innovative approach to achieve efficient hydrogen production while concurrently generating value-added chemicals. Herein, we report an energy-saving H2 production system utilizing electrooxidation of glycerol to generate valuable formate. Cobalt–ruthenium oxide nanosheet arrays (CoRuO/CF) and cobalt–ruthenium bimetallic nanoparticles wrapped by nitrogen-doped carbon nanosheet arrays (CoRuCN/CF) were synthesized for glycerol oxidation reaction (GOR) and hydrogen evolution reaction (HER), respectively, using Co-ZIF nanosheets precursor material supported on copper foam (Co-ZIF/CF) as the substrate. Remarkably, the hybrid electrolysis system can achieve a current density of 10 mA cm−2 with only 1.19 V, which is significantly lower than that required by traditional water-splitting systems. This work demonstrates the promising potential of efficiently utilizing biomass energy and achieving a sustainable production process for fine chemical products.

Rational Design and Facile Preparation of Palladium-Based Electrocatalysts for Small Molecules Oxidation.

Direct liquid fuel cells (DLFCs) can convert the chemical energy of small organic molecules directly into electrical energy, which is a promising technique and always calls for electrocatalysts with high activity, stability and selectivity. Palladium (Pd)-based catalysts for DLFCs have been widely studied with the pursuit of ultra-high performance, however, most of the preparation routes require complex agents, multi-operation steps, even extreme experimental conditions, which are high-cost, energy-consuming, and not conducive to the scalable and sustainable production of catalysts. In this review, the recent progresses on not only the rational design strategies, but also the facile preparation methods of Pd-based electrocatalysts for small molecules oxidation reaction (SMOR) are comprehensively summarized. Based on the principles of green chemistry in material synthesis, the basic rules of "facile method" have been restricted, and the fabrication processes, perks and drawbacks, as well as practical applications of the "real" facile methods have been highlighted. The landscape of this review is to facilitate the mild preparation of efficient Pd-based electrocatalysts for SMOR, that is, to achieve a balance between "facile preparation" and "outstanding performance", thereby to stimulate the huge potential of sustainable nano-electrocatalysts in various research and industrial fields.

Expansion of Auxiliary Activity Family 5 sequence space via biochemical characterization of six new copper radical oxidases.

Bacterial and fungal copper radical oxidases (CROs) from Auxiliary Activity Family 5 (AA5) are implicated in morphogenesis and pathogenesis. The unique catalytic properties of CROs also make these enzymes attractive biocatalysts for the transformation of small molecules and biopolymers. Despite a recent increase in the number of characterized AA5 members, especially from subfamily 2 (AA5_2), the catalytic diversity of the family as a whole remains underexplored. In the present study, phylogenetic analysis guided the selection of six AA5_2 members from diverse fungi for recombinant expression in Komagataella pfaffii (syn. Pichia pastoris) and biochemical characterization in vitro. Five of the targets displayed predominant galactose 6-oxidase activity (EC 1.1.3.9), and one was a broad-specificity aryl alcohol oxidase (EC 1.1.3.7) with maximum activity on the platform chemical 5-hydroxymethyl furfural (EC 1.1.3.47). Sequence alignment comparing previously characterized AA5_2 members to those from this study indicated various amino acid substitutions at active site positions implicated in the modulation of specificity.IMPORTANCEEnzyme discovery and characterization underpin advances in microbial biology and the application of biocatalysts in industrial processes. On one hand, oxidative processes are central to fungal saprotrophy and pathogenesis. On the other hand, controlled oxidation of small molecules and (bio)polymers valorizes these compounds and introduces versatile functional groups for further modification. The biochemical characterization of six new copper radical oxidases further illuminates the catalytic diversity of these enzymes, which will inform future biological studies and biotechnological applications.

Small Molecule Oxidation Facilitated Seawater Splitting for Hydrogen Production: Opportunities and Challenges

Direct seawater splitting is an environment‐friendly and promising technology to replace freshwater electrolysis for hydrogen production. The challenge of seawater electrolysis lies in the competition between chloride oxidation reaction (CER) and oxygen evolution reaction (OER), as well as electrode corrosion and poisoning caused by chloride. Some small molecules have lower anodic electrocatalytic oxidation potentials compared to OER and CER, making them possible to substitute OER and/or CER in coupled electrolyzers not only to eliminate the electrode corrosion problem but also to significantly enhance the energy efficiency of seawater electrolysis. This article reviews the progress of such small molecule oxidation facilitated seawater electrolyzer. Starting with an overview of the key challenges in seawater electrolysis, this review introduces the fundamentals and advantages of the coupled seawater electrolyzers and discusses the strategies for anodic small molecule oxidation and cathodic hydrogen evolution reaction, including utilizing Cl‐ as a reactive medium, value‐added chemical synthesis, pollutants electrooxidation, and optimizing electrolyzers. Finally, the challenges and prospects of small molecule oxidation facilitated seawater splitting are summarized, aiming to provide impetus for research and development on coupled seawater electrolysis technologies.

Bimetallic electrocatalysts based on polyoxometalate for hydrogen evolution and urea oxidation reaction

Electrochemical water decomposition is an efficient and environmentally friendly method for producing hydrogen. Because of the high voltage required for water electrolysis, using anodic urea oxidation process (UOR) to replace the oxygen evolution reaction can significantly cut energy usage. In this paper, hydrogen evolution reaction (HER) and urea oxidation process (UOR) electrocatalysts were synthesized by one-step carbonization using giant polyoxomolybdate cluster Mo132 and triethylamine at different temperatures. Ni/MoN@NC obtained at 800 °C shows good HER effect in the acidic electrolyte, an overpotential of 94 mV can provide the current density of 10 mA cm−2. Ni/NiO@NC obtained by calcination at 400 °C exhibits good UOR performance, in which the potential is 1.41 V when the current density is 10 mA cm−2. Efficient HER performance depends on the synergy of Ni and MoN. The highly efficient UOR is derived from the hierarchical structure of Ni and NiO. Furthermore, the porous structure also enhances the full contact between electrolyte and active sites, the catalytic performance of the catalyst was improved benefit to improve the catalytic activity. This work affords a general approach to simply synthesize efficient hydrogen producing materials for HER and small molecules oxidation fields.

Nickel Hydroxide-Based Electrocatalysts for Promising Electrochemical Oxidation Reactions: Beyond Water Oxidation.

Transition metal hydroxides have attracted significant research interest for their energy storage and conversion technique applications. In particular, nickel hydroxide (Ni(OH)2), with increasing significance, is extensively used in material science and engineering. The past decades have witnessed the flourishing of Ni(OH)2-based materials as efficient electrocatalysts for water oxidation, which is a critical catalytic reaction for sustainable technologies, such as water electrolysis, fuel cells, CO2 reduction, and metal-air batteries. Coupling the electrochemical oxidation of small molecules to replace water oxidation at the anode is confirmed as an effective and promising strategy for realizing the energy-saving production. The physicochemical properties of Ni(OH)2 related to conventional water oxidation are first presented in this review. Then, recent progress based on Ni(OH)2 materials for these promising electrochemical reactions is symmetrically categorized and reviewed. Significant emphasis is placed on establishing the structure-activity relationship and disclosing the reaction mechanism. Emerging material design strategies for novel electrocatalysts are also highlighted. Finally, the existing challenges and future research directions are presented.

Nickel–cobalt oxide nanoparticles as superior electrocatalysts for enhanced coupling hydrogen evolution and selective ethanol oxidation reaction

The selective oxidation of organic small molecules not only promotes cathodic hydrogen production, but also acts as an alternative reaction to the anodic oxygen evolution reaction of electrolytic water, producing value-added products at the anode.

Progress in metal-organic frameworks for small molecule oxidative coupled hydrogen production

The electrochemical oxidation reactions of small molecules present a lower theoretical thermodynamic potential in comparison to the oxygen evolution reaction (OER) and can serve as a viable alternative, concurrently generating value-added compounds or facilitating pollutant degradation. Metal-organic frameworks (MOFs) have garnered significant attention due to their adjustable properties, abundant active sites, and wide porosity in recent years. In comparison with conventional electrocatalysts, MOF-based electrocatalysts exhibit superior performance in the field of small molecule oxidation. A comprehensive review of synthesis methods and strategies for enhancing the electrochemical properties of MOF-based electrocatalysts has been provided, focusing on their applications in small molecule oxidation coupled with the hydrogen evolution reaction (HER). Furthermore, we address the current challenges and prospects to promote the development of more efficient MOF-based electrocatalysts for water splitting assisted by small molecule oxidation.

Insights into mechanisms on electrochemical oxygen evolution substitution reactions

The high total energy consumption of water electrolysis systems is often attributed to the slow kinetics of oxygen evolution reaction (OER). To address this issue, substituting small molecule oxidation reaction that is thermodynamically more advantageous for OER at the anode can significantly increase its energy conversion efficiency. Diversified oxidation substrates can ensure efficient conversion of the cathodic reaction while generating high value-added products or pollutant degradation at the anode. However, the complexity of the elemental composition of the substrate requires an in-depth study of the reaction mechanism. This review focuses on the mechanism of electrooxidation of different substrate molecules, such as ethanol, urea, and hydrazine. Additionally, it introduces some design ideas and strategies for high-performance electrocatalysts in conjunction with reaction path selectivity. The work also foresees the challenges in achieving industrial transformation in this field.

Synergistic engineering of heteroatom doping and heterointerface construction in V-doped Ni(OH)2/FeOOH to boost both oxygen evolution and urea oxidation reactions

The exploitation of cost-effective and abundant non-noble metal electrocatalysts holds great significances in enhancing the efficiency of oxygen evolution reaction (OER) and/or urea oxidation reaction (UOR). Herein, we report an electrocatalyst with co-existing V-dopants and Ni(OH)2/FeOOH interfaces (referred to as A-NiFeV/NF, with “A” indicating “activated”). The electron coupling between Ni, Fe and V, analyzed through X-ray photoelectron spectroscopy, indicates that Ni and Fe both receive electrons from the V. Additionally, the Fe can also lead to a bias toward a lower valence of the Ni centers in Ni(OH)2. Further in situ Raman spectroscopy reveals that Ni2+(OH)2 inevitably undergoes transformation into amorphous Ni3+OOH during the activation process, however, the synergistic effects of V-dopants and Ni(OH)2/FeOOH interfaces keep the Ni centers mostly in a lower oxidation state of +2 even at high potential ranges. These low-valence Ni centers are proposed to be positively correlated with the optimized OER activity of the Ni-based electrocatalysts. As a result, the designed A-NiFeV/NF electrocatalyst exhibits low overpotentials of 234 and 313 mV to propel current densities of 10 and 100 mA/cm2, and a small Tafel slope of 37.8 mV/dec for OER in 1.0 M KOH. The catalyst demonstrates a stable OER activity for over 100 h at 100 mA/cm2. Additionally, it can be integrated with a solar cell to construct a solar-driven electrolytic OER device without additional electric input. Similarly, for the small molecule oxidation, UOR, only ∼1.33 and ∼1.39 V vs. RHE (RHE: reversible hydrogen electrode) are required to achieve 10 and 100 mA/cm2, respectively, in an electrolyte composed of 1.0 M KOH with 0.33 M urea.

The Influence of the Reaction Conditions on the Photocatalytic Gas‐Phase Conversion of Methanol with Water Vapor over Pt/SrTiO3 in a Continuously Operated Flow Reactor

AbstractContinuous methanol photooxidation in the gas phase is a promising method to produce valuable chemicals like formaldehyde or methyl formate in addition to hydrogen under mild conditions. The influence of the reaction conditions on the selectivity of methanol oxidation to formaldehyde is studied using a heated flat‐plate flow photoreactor illuminated by an LED array (λmax = 368 nm) and Pt‐modified SrTiO3. A combination of online analytical methods allowed to quantify all gaseous products during extended time‐on‐stream (> 48 h TOS). The selectivity to formaldehyde is found to be primarily determined by the residence time and the process temperature. At a low methanol to water ratio, methanol conversion and evolution of CO2 are favored, whereas the light intensity primarily influenced the apparent quantum yield from 5.1 to 1.8% at 9.36 to 52.93 mW cm−2, respectively, and the methanol conversion thus determining the economic efficiency of the process. Operation temperatures higher than 110 °C resulted in a strong deactivation of the catalyst while simultaneously the formation of CO at the expense of formaldehyde selectivity is favored. This study demonstrates the importance of understanding the influence of relevant reaction conditions and the potential of selective photocatalytic gas‐phase oxidation of small molecules.

Etched High-Entropy Prussian Blue Analogues as Trifunctional Catalysts for Water, Ethanol, and Urea Electrooxidation.

The introduction of high-entropy and high specific surface area into Prussian blue analogues (PBAs) has yet to create interest in the field of electrocatalytic small-molecule oxidation reactions. Herein, we synthesize a novel class of high-entropy (HE) PBAs with a high specific surface area via a simple NH3·H2O-etching strategy and systematically investigate the electrocatalytic performance of HE-PBA toward electrocatalytic water, ethanol, and urea oxidation reactions. Importantly, the NH3·H2O-etched HE-PBA (denoted as HE-PBA-e) demonstrated enhanced electrocatalytic performance toward small-molecule oxidation compared to the pristine HE-PBA, reaching 10 mA cm-2 with potentials of 1.56, 1.41, and 1.37 V for the oxygen evolution reaction (OER), ethanol oxidation reaction (EOR), and urea oxidation reaction (UOR), respectively. Deep characterizations suggest that the NH3·H2O etching treatment not only creates rich nanopores to enlarge the surface area and boosts the mass transport and electron transfer but also facilitates the formation of high-valence metal oxides to improve the intrinsic activity. This demonstration of how systematically increasing the high oxidation state of metals will serve as a governing principle for the rational design of more advanced HE-PBAs toward the electrooxidation of small molecules.

Two-dimensional iron porphyrin nanozyme mimics cytochrome P450 activity for cancer proliferation inhibition

Two-dimensional materials have excellent performance in energy catalysis and biomedicine due to their unique advantages in surface and interfacial properties. Taking into account the unique advantages of the surface interface and catalysis of two-dimensional materials, it is a very feasible way to construct two-dimensional materials with clear atomic structure to break the redox balance in tumor cells, so as to achieve efficient anti-tumor effects. Based on this, we selected the porphyrin ligands that widely exist in nature, equipped with iron metal active centers, and constructed a two-dimensional iron porphyrin nanozyme with a clear atomic structure, which simulated the redox activity of cytochrome P450 enzymes. The experimental results show that by carrying a rotatable pyridine group on the porphyrin ring, the iron porphyrin monomers can be effectively connected and expanded into a two-dimensional iron porphyrin microstructure. Enough iron centers are exposed on the surface of two-dimensional iron porphyrins as catalytic sites. In the presence of oxidants, two-dimensional iron porphyrins can efficiently catalyze the oxidation of small organic molecules, and have good P450-like enzymatic activity. At the same time, the two-dimensional iron porphyrin nanomaterial was used for anti-tumor, and it was found that it has an efficient ability to inhibit tumor proliferation, which may be due to the catalytic oxidation of various organic small molecules in tumor cells by the high concentration of hydrogen peroxide in tumor cells. At the same time, we found that the two-dimensional iron porphyrin nanozyme may have a good drug loading capacity due to the many exposed iron sites on its surface, which provides a possible option for drug loading to achieve combined high-efficiency tumor therapy.

Design of earth‐abundant amorphous transition metal‐based catalysts for electrooxidation of small molecules: Advances and perspectives

AbstractElectrochemical oxidation of small molecules (e.g., water, urea, methanol, hydrazine, and glycerol) has gained growing scientific interest in the fields of electrochemical energy conversion/storage and environmental remediation. Designing cost‐effective catalysts for the electrooxidation of small molecules (ESM) is thus crucial for improving reaction efficiency. Recently, earth‐abundant amorphous transition metal (TM)‐based nanomaterials have aroused souring interest owing to their earth‐abundance, flexible structures, and excellent electrochemical activities. Hundreds of amorphous TM‐based nanomaterials have been designed and used as promising ESM catalysts. Herein, recent advances in the design of amorphous TM‐based ESM catalysts are comprehensively reviewed. The features (e.g., large specific surface area, flexible electronic structure, and facile structure reconstruction) of amorphous TM‐based ESM catalysts are first analyzed. Afterward, the design of various TM‐based catalysts with advanced strategies (e.g., nanostructure design, component regulation, heteroatom doping, and heterostructure construction) is fully scrutinized, and the catalysts’ structure‐performance correlation is emphasized. Future perspectives in the development of cost‐effective amorphous TM‐based catalysts are then outlined. This review is expected to provide practical strategies for the design of next‐generation amorphous electrocatalysts.

Recent progress in intermetallic nanocrystals for electrocatalysis: From binary to ternary to high‐entropy intermetallics

AbstractDeveloping sustainable and clean energy‐conversion techniques is one of the strategies to simultaneously meet the global energy demand, save fossil fuels and protect the environment, in which nanocatalysts with high activity, selectivity and durability are of great importance. Intermetallic nanocrystals, featuring their ordered atomic arrangements and predictable electronic structures, have been recognized as a type of active and durable catalysts in energy‐related applications. In this minireview, the very recent progress in the syntheses and electrocatalytic applications of noble metal‐based intermetallic nanocrystals is summarized. Various synthetic strategies, including the conventional thermal annealing approach and its diverse modifications, as well as the wet‐chemical synthesis, for the construction of binary, ternary and high‐entropy intermetallic nanocrystals have been discussed with representative examples, highlighting their strengths and limitations. Then, their electrocatalytic applications toward oxygen reduction reaction, small molecule oxidation reactions, hydrogen evolution reaction, CO2/CO reduction reactions, and nitrogen reduction reaction are discussed, with the emphasis on how the ordered intermetallic structures contribute to the enhanced performance. We conclude the minireview by addressing the current challenges and opportunities of intermetallic nanocrystals in terms of syntheses and electrocatalytic applications.

Electrochemical Properties and Perspectives of Nickel(II) and Cobalt(II) Coordination Polymers-Aspects and an Application in Electrocatalytic Oxidation of Methanol

The electrochemical sensing potential of two isostructural one-dimensional nickel(II) and cobalt(II) coordination polymers with 4,4′-bipyridine (4,4′-bpy) and 6-oxonicotinate (6-Onic), namely, {[Ni(4,4′-bpy)(H2O)4](6-Onic)2×2H2O}n and {[Co(4,4′-bpy)(H2O)4](6-Onic)2×2H2O}n, was investigated along with the polymers’ potential applications in the catalytic oxidation of methanol. The highly oxidative species from redox pairs Ni(II)/Ni(III) and Co(II)/Co(III) in these compounds represent catalytically active centres for oxidation of small molecules. A glassy carbon electrode (GCE) modified with a Ni polymer showed stability and reproducibility in 0.1 M NaOH, while the oxidation current inc 2reased with the increasing methanol concentration, suggesting that the Ni-polymer-modified electrode possess good sensing ability with respect to methanol. The GC electrode modified with the Co polymer is not reproducible and cannot be used for electroanalytical purposes under these experimental conditions. The GC electrode modified with the Ni polymer was successfully applied in the determination of methanol. This method showed favourable linear concentration dependence with a good sensitivity of 2.65 and 11.0 mA mM−1, a wide concentration range (0.001–4 mM), and a detection limit of 0.8 μM, which indicates its excellent application potential for methanol oxidation and thus its determination.

High efficient trifunctional electrocatalyst based on bimetallic oxide with rich oxygen vacancies towards electrochemical oxidation of small molecules at high current density

Exploiting low-cost, high-activity and robust-stability catalysts has become a meaningful and challenging research topic in the development of hydrogen production via electrochemical water splitting, meanwhile the as-synthesized materials exhibiting multi-functional electrocatalytic performance is highly desirable, but remains tremendous difficulty. Herein, a facile and scalable strategy is developed to synthesize nanowire-like NiCo2O4 arrays with space group Fd3¯m in-situ grown on cobalt foam (denoted as NiCo2O4/CF) via hydrothermal approach and air calcination treatment. The as-prepared nanoporous NiCo2O4/CF electrode possesses a high specific surface area, multiple redox couples and rich oxygen vacancies, thus displaying excellent tri-profitable catalytic activities towards hydrazine oxidation reaction (HzOR), urea oxidation reaction (UOR) and methanol oxidation reaction (MOR). Experimental results show that affording current densities of 10 and 100 mA cm−2 needs potentials of −0.172 and −0.149 V for HzOR, delivering 100 and 500 mA cm−2 current densities merely requires low potentials of 1.343 and 1.440 V for UOR. Impressively, for MOR, a potential of only 1.5 V is required to achieve a high current density of 1058 mA cm−2, outperforming most of the reported electrocatalysts. What's more, the NiCo2O4/CF electrode exhibits exceptional stability at a high current density of 100 mA cm−2 over 20 h for all of the three small molecules electro-oxidation. The current work provides a promising application opportunity for the nanowire-like NiCo2O4 in the aspect of energy-saving hydrogen generation with the assistance of small molecule electro-oxidation reaction.

Progress in Hydrogen Production Coupled with Electrochemical Oxidation of Small Molecules.

The electrochemical oxidation of small molecules to generate value-added products has gained enormous interest in recent years because of the advantages of benign operation conditions, high conversion efficiency and selectivity, the absence of external oxidizing agents, and eco-friendliness. Coupling the electrochemical oxidation of small molecules to replace oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode in an electrolyzer would simultaneously realize the generation of high-value chemicals or pollutant degradation and the highly efficient production of hydrogen. This Minireview presents an introduction on small-molecule choice and design strategies of electrocatalysts as well as recent breakthroughs achieved in the highly efficient production of hydrogen. Finally, challenges and future orientations are highlighted.

Progress in Hydrogen Production Coupled with Electrochemical Oxidation of Small Molecules

AbstractThe electrochemical oxidation of small molecules to generate value‐added products has gained enormous interest in recent years because of the advantages of benign operation conditions, high conversion efficiency and selectivity, the absence of external oxidizing agents, and eco‐friendliness. Coupling the electrochemical oxidation of small molecules to replace oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode in an electrolyzer would simultaneously realize the generation of high‐value chemicals or pollutant degradation and the highly efficient production of hydrogen. This Minireview presents an introduction on small‐molecule choice and design strategies of electrocatalysts as well as recent breakthroughs achieved in the highly efficient production of hydrogen. Finally, challenges and future orientations are highlighted.

Intermediate-Temperature Alkane Electrochemical Activation

Electrochemical activation of alkanes plays an enabling role for applications ranging from fuel cells to electro-production of materials and chemicals. Intermediate-temperature (>200 oC) electrochemical devices have improved diffusions, reaction kinetics, and feedstock flexibility. In this contribution, we present the electrochemical activation of alkanes using intermediate-temperature electrochemical devices. Our work is inspired by Duan et al. whose work showed that alkanes can be oxidized as fuel in protonic ceramic fuel cells1. We extend this concept and evaluate whether this electrochemical activation can activate longer-chain hydrocarbons to form industrial gases. We present a comparison of the electrochemical approach to pyrolysis, and in particular, its selectivity. Different electrocatalysts will be evaluated to test both electrochemical and thermal oxidation. Finally, we use small-molecule oxidation experiments to probe how the thermochemical reactions occur in parallel with the electrochemical conversion. We identify the products from these processes and propose the alkane activation mechanism. Duan, C.; Kee, R. J.; Zhu, H.; Karakaya, C.; Chen, Y.; Ricote, S.; Jarry, A.; Crumlin, E. J.; Hook, D.; Braun, R.; Sullivan, N. P.; O’Hayre, R., Highly durable, coking and sulfur tolerant, fuel-flexible protonic ceramic fuel cells. Nature 2018, 557 (7704), 217-222.