Oxidation Of Small Organic Molecules Research Articles

EFFECT OF SNO2 POROUS STRUCTURE ON ITS OPTICAL AND PHOTOELECTROCHEMICAL PROPERTIES IN WATER AND WATER-METHANOL SOLUTIONS

Tin(IV) oxide is a wide-gap semiconductor material that is widely used in photooxidation reactions of organic compounds. However, the relationship between energetic and photoelectrocatalytic properties in the oxidation of small organic molecules has not yet been sufficiently explored. In this work, a series of tin oxides were synthesized using hydrothermal, sol-gel, and template methods. Polystyrene spheres with a size of 250 nm, as well as cetyltrimethylammonium bromide, were used as templates. X-Ray diffraction, low-temperature nitrogen adsorption, X-ray photoelectron spectroscopy, Raman spectroscopy and diffuse reflectance spectroscopy methods were used to study the structure, surface composition, optical and energy characteristics. Using photoelectrochemical methods, the potentials of the conduction band and valence band were determined, and photocurrents in aqueous and aqueous-methanol solutions were studied depending on electrode polarization. It is shown that the preparation method (sol-gel or hydrothermal) does not affect the position of energy bands, while the use of a template during synthesis leads to an increase in the average pore diameter in the samples and an increase in photocurrent values in the presence of methanol. It has been established that for template-synthesized samples, the magnitude of photocurrents in a water-methanol mixture increases with an increase in the valence-band potential. The sample prepared by the hydrothermal method using a template showed the highest photocurrent values both in the background electrolyte (17.3 μA/cm2) and in the presence of methanol (26 μA/cm2), compared to the sample prepared without using a template in the electrolyte with the addition of methanol (7.6 μA/cm2) and without it (7.8 μA/cm2).

Investigation of the Activity and Stability of Manganese-Based Electrocatalysts for the Electrochemical Oxidation of Water and Small Organic Molecules in Acidic Electrolyte

Water electrolysis is a crucial process for hydrogen production, providing a clean and sustainable method for H2 production. Iridium-based catalysts are particularly effective in promoting the oxygen evolution reaction (OER) that takes place at the anode of electrolyzers. The unique properties of iridium make it well-suited for this purpose, but its high cost becomes a bottleneck in making water electrolysis economically viable on a large scale. Manganese-based electrocatalysts have emerged as promising candidates for the OER, mainly due to their earth abundance, low toxicity, and activity. It has been shown that manganese oxide can operate stably in acid, in a restricted potential window, where the formation of permanganate ions is avoided. Thus, for practical application, the stability must be improved, so a larger potential window can be employed. To address this challenge, some approaches have emerged from combining a catalytically active, but instable oxide, with the one that is stable, but inactive for the OER. In the presentation, we will show the results of activity, stability, and faradaic efficiency (FE) for O2 formation for water electro-oxidation on manganese oxide, and on manganese oxide combined with antimony, tin, titanium, niobium, and silicon oxide. The faradaic efficiencies, determined via EC-MS (Electrochemistry coupled to mass spectrometry) measurements revealed that manganese antimonate and pure manganese oxide have the highest values for O2 formation, with the former presenting higher stability at high overpotentials. We will discuss the obtained trends in stability and FEs for the other synthesized oxides. Additionally, for these two most efficient electrocatalysts, EC-MS measurements were conducted for the electrochemical oxidation of some small organic molecules, such as formic acid, methanol, ethanol, and ethylene glycol (electrochemical reforming for H2 production). The results showed that the selectivity for the electro-oxidation of water and/or of the organic molecule (monitoring the formation of CO2) strongly depends on the catalyst composition and on the number of carbon atoms of the molecule. We will further discuss, in the presentation, the factors that govern the selectivity and stability for each case. The obtained results of this study may be helpful for developing more efficient, selective and, mainly, more stable earth-abundant electrocatalysts for electrolyzers.

Voltammetric quantification of H:Pd ratio complicated by α↔β phase transition in PdHx: Electrodes with low Pd loadings

The Pd hydride (PdHx) is a typical system to study the fundamentals of solute intercalation and phase transformations or to determine the effect of strain on the rate of electrocatalytic reactions. A crucial methodological aspect, however, involves quantitatively determining the hydrogen-to-palladium atomic ratio (H:Pd) under experimental conditions where various incidental contributions to the total electrode charge are comparable to the charge spent for H adsorption/absorption and desorption. This is the case for electrodes with relatively low (dozens of μg/cm2) loadings of Pd on various porous supports, typically used to study the oxidation of small organic molecules or the reduction of oxygen in acidic or alkaline fuel cells. Ultra-low Pd loadings (often in the range of a few μg/cm2) are also typical for Pd nanoparticles on smooth supports, which are commonly considered as model systems for in situ structural studies of hydrogen sorption. To determine accurately the H content in Pd particles, we propose a technique based on analysis of charge disbalance at anodic and cathodic scans of a cyclic voltammogram, and also address the contribution of adsorbed H. To illustrate the possibilities and limitations of this technique, we present the voltametric study of thin electrodeposited Pd layers on glassy carbon and of a carbon-supported Pd catalyst.

(Invited) 25 Years of the Thin-Film Rotating Disk Electrode Technique

Twenty-five years ago, in summer 1998, the first paper introducing the thin-film rotating disk electrode (TFRDE) method was published in the Journal of the Electrochemical Society [1]. At this time, we demonstrated that by preparing a thin layer of a supported Pt/Vulcan catalyst mixed with a small amount of Nafion could reliably be coated on top of a glassy carbon disk, electrochemical reactions like the hydrogen oxidation reaction could be measured on an RDE taking advantage of the well-known mass-transport conditions of an RDE. By keeping the layer thickness in the range of 1 micrometer, additional mass-transport resistances induced by the catalyst layer/Nafion film became negligible. That is, all equations valid on an RDE could be applied without modification. Further work on the oxygen reduction reaction by using the TF Rotating Ring-Disk electrode allowed detecting peroxide formation on a supported catalyst [2]. Both publications grounded the path for catalyst development in fuel cell. The method has been used since then as a standard method for catalyst screening and characterization in both academia and industries. In addition, many researchers improved the TFRDE method within their research. The application span of the TFRDE developed from fuel cell research, oxidation of small organic molecules, to work on Li-O2 batteries, water electrolysis, and CO2 reduction.This presentation will offer a journey over the last 25 years and the application of the TFRDE technique in catalyst development and characterization.[1] T.J. Schmidt, H.A. Gasteiger, G.D. Stäb, P. Urban, D.M. Kolb, R.J. Behm Characterization of High-Surface-Area Electrocatalysts Using a Rotating Disk Electrode Configuration J. Electrochem. Soc. 145 (1998) 2354-2358 [2] U.A. Paulus, T.J. Schmidt, H.A. Gasteiger, R.J. Behm Oxygen Reduction on a High-Surface Area Pt/Vulcan Carbon Catalyst: A Thin-Film Rotating Ring-Disk Study J. Electroanal. Chem. 495 (2001) 134-145 [3] T.J. Schmidt, H.A. Gasteiger Rotating Thin-Film Method for Supported Catalysts, in Handbook of Fuel Cells: Fundamentals, Technology and Applications, Vol. 2 Part 3, W. Vielstich, H.A. Gasteiger, A. Lamm (Eds.), John Wiley & Sons, New York, 316-333 (2003)

Beneficial Effect of Acetic Acid on the Formation of FeIII(OOH) Species and on the Catalytic Activity of Bioinspired Nonheme FeII Complexes.

AbstractThree new amine/pyridine FeII complexes bearing pentadentate ligand with one, two or three electron enriched 4‐methoxy‐3,5‐dimethylpyridine were used as catalysts for the oxidation of small organic molecules by hydrogen peroxide. The distribution of products formed suggests that these ligands are not enough electron donating to promote the O−O heterolytic cleavage of the oxidant in order to generate selective FeV(O) species. Using acetic acid in the reaction mixtures results in a significant increase of the efficiency of these catalytic systems. Our investigations show that the use of AcOH leads to the protonation/dissociation of a pyridyl moiety and the formation of (N4)FeII(OAc)(OH) species. These complexes readily react with excess hydrogen peroxide to yield (N4)FeIII(OAc)(OOH) intermediates. These latter intermediates are proposed to evolve into (N4)FeIV(OAc)(O), which are more efficient than the usual (N4)FeIV(O) and (N5)FeIV(O).

Composition-Dependent Electrocatalytic Behavior in First-Transition Metal Nanowires Toward the Oxidation of Small Organic Molecules

Platinum-based catalysts are widely used for the electrochemical oxidation of small organic molecules (SOMs), including methanol, ethanol, and glucose. However, it has some limitations, including high cost and limited availability. Platinum’s performance is also hindered by the formation of carbon monoxide (CO) and other partially oxidized intermediates that strongly bind to the surface and hinder kinetics at low overpotentials. Binary alloys created from Pt and other more abundant transition metals aim to reduce the cost of Pt catalysts as well as alleviate the effects of the CO intermediate on Pt catalysts, thus enhancing the catalytic performance of pure Pt. In this project, we synthesize, characterize, and evaluate the electrocatalytic performance of one-dimensional electrocatalysts created from transition metal nanowires coated with precious metal catalysts. These core-shell NWs were synthesized using a template-based technique that allows for the creation of nanowires of different sizes and compositions. The nanowires were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and powder X-ray diffraction (XRD). The catalytic performance of these NWs toward SOM oxidation was evaluated in acidic conditions utilizing cyclic voltammetry and linear sweep voltammetry. We also investigate the performance of these catalysts toward the oxygen reduction reaction (ORR) utilizing rotating disk electrode measurements. The results reveal that the characteristics of the catalytic performance of the alloy NWs are dependent on their morphology and composition.

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.

Boosting Electrocatalytic Oxidation of Formic Acid on Ir(IV)-Doped PdAg Alloy Nanodendrites with Sub-5 nm Branches.

The formic acid oxidation reaction (FAOR) represents an important class of small organic molecule oxidation and is central to the practical application of fuel cells. In this study, we report the fabrication of Ir(IV)-doped PdAg alloy nanodendrites with sub-5 nm branches via stepwise synthesis in which the precursors of Pd and Ag were co-reduced, followed by the addition of IrCl3 to conduct an in situ galvanic replacement reaction. When serving as the electrocatalyst for the FAOR in an acidic medium, Ir(IV) doping unambiguously enhanced the activity of PdAg alloy nanodendrites and improved the reaction kinetics and long-term stability. In particular, the carbon-supported PdAgIr nanodendrites exhibited a prominent mass activity with a value of 1.09 A mgPd-1, which is almost 2.0 times and 2.7 times that of their PdAg and Pd counterparts, and far superior to that of commercial Pt/C. As confirmed by the means of the DFT simulations, this improved electrocatalytic performance stems from the reduced overall barrier in the oxidation of formic acid into CO2 during the FAOR and successful d-band tuning, together with the stabilization of Pd atoms. The current study opens a new avenue for engineering Pd-based trimetallic nanocrystals with versatile control over the morphology and composition, shedding light on the design of advanced fuel cell electrocatalysts.

Selective Ethylene Glycol Oxidation to Formate on Nickel Selenide with Simultaneous Evolution of Hydrogen.

There is an urgent need for cost-effective strategies to produce hydrogen from renewable net-zero carbon sources using renewable energies. In this context, the electrochemical hydrogen evolution reaction can be boosted by replacing the oxygen evolution reaction with the oxidation of small organic molecules, such as ethylene glycol (EG). EG is a particularly interesting organic liquid with two hydroxyl groups that can be transformed into a variety of C1 and C2 chemicals, depending on the catalyst and reaction conditions. Here, a catalyst is demonstrated for the selective EG oxidation reaction (EGOR) to formate on nickel selenide. The catalyst nanoparticle (NP) morphology and crystallographic phase are tuned to maximize its performance. The optimized NiS electrocatalyst requires just 1.395V to drive a current density of 50 mAcm-2 in 1m potassium hydroxide (KOH) and 1m EG. A combination of in situ electrochemical infrared absorption spectroscopy (IRAS) to monitor the electrocatalytic process and ex situ analysis of the electrolyte composition shows the main EGOR product is formate, with a Faradaic efficiency above 80%. Additionally, C2 chemicals such as glycolate and oxalate are detected and quantified as minor products. Density functional theory (DFT) calculations of the reaction process show the glycol-to-oxalate pathway to be favored via the glycolate formation, where the CC bond is broken and further electro-oxidized to formate.

Controlled synthesis of MOF-derived hollow and yolk–shell nanocages for improved water oxidation and selective ethylene glycol reformation

Delicately designed metal–organic framework (MOF)-derived nanostructured electrocatalysts are essential for improving the reaction kinetics of the oxygen evolution reaction and tuning the selectivity of small organic molecule oxidation reactions. Herein, novel oxalate-modified hollow CoFe-based layered double hydroxide nanocages (h-CoFe-LDH NCs) and yolk–shell ZIF@CoFe-LDH nanocages (ys-ZIF@CoFe-LDH NCs) are developed through an etching–doping reconstruction strategy from a Co-based MOF precursor (ZIF-67). The distinctive nanostructures, along with the incorporation of the secondary metal element and intercalated oxalate groups, enable h-CoFe-LDH NCs and ys-ZIF@CoFe-LDH NCs to expose more active sites with high intrinsic activity. The resultant h-CoFe-LDH NCs exhibit outstanding OER activity with an overpotential of only 278 ​mV to deliver a current density of 50 ​mA ​cm−2. Additionally, controlling the reconstruction degree enables the formation of ys-ZIF@CoFe-LDH NCs with a yolk–shell nanocage nanostructure, which show outstanding electrocatalytic performance for the selective ethylene glycol oxidation reaction (EGOR) toward formate, with a Faradaic efficiency of up to 91%. Consequently, a hybrid water electrolysis system integrating the EGOR and the hydrogen evolution reaction using Pt/C||ys-ZIF@CoFe-LDH NCs is explored for energy-saving hydrogen production, requiring a cell voltage 127 ​mV lower than water electrolysis to achieve a current density of 50 ​mA ​cm−2. This work demonstrates a feasible way to design advanced MOF-derived electrocatalysts toward enhanced electrocatalytic reactions.

The electrostatic effect and its role in promoting electrocatalytic reactions by specifically adsorbed anions.

The adsorption of anions and its impact on electrocatalytic reactions are fundamental topics in electrocatalysis. Previous studies revealed that adsorbed anions display an overall poisoning effect in most cases. However, for a few reactions such as the hydrogen evolution reaction (HER), oxidation of small organic molecules (SOMs), and reduction of CO2 and O2, some specifically adsorbed anions can promote their reaction kinetics under certain conditions. The promotion effect is frequently attributed to the adsorbate induced modification of the nature of the active sites, the change of the adsorption configuration and free energy of the key reactive intermediate which consequently change the activation energy, the pre-exponential factor of the rate determining step etc. In this paper, we will give a mini review of the indispensable role of the classical double layer effect in enhancing the kinetics of electrocatalytic reactions by anion adsorption. The ubiquitous electrostatic interactions change both the potential distribution and the concentration distribution of ionic species across the electric double layer (EDL), which alters the electrochemical driving force and effective concentration of the reactants. The contribution to the overall kinetics is highlighted by taking HER, oxidation of SOMs, reduction of CO2 and O2, as examples.

Yttrium-based Double Perovskite Nanorods for Electrocatalysis.

Herein, we investigate the effect of the chemical composition of double perovskite nanorods on their versatile electrocatalytic activity not only as supports for the oxidation of small organic molecules but also as catalysts for the oxygen evolution reaction. Specifically, Y2CoMnO6 and Y2NiMnO6 nanorods with average diameters of 300 nm were prepared by a two-step hydrothermal method, in which the individual effects of synthetic parameters, such as the pH, annealing temperature, and precursor ratios on both the composition and morphology, were systematically investigated. When used as supports for Pt nanoparticles, Y2CoMnO6/Pt catalysts exhibited an electrocatalytic activity for the methanol oxidation reaction, which is 2.1 and 1.3 times higher than that measured for commercial Pt/C and Y2NiMnO6/Pt, respectively. Similarly, the Co-based catalyst support material displayed an ethanol oxidation activity, which is 2.3 times higher than both Pt/C and Y2NiMnO6/Pt. This clear enhancement in the activity for Y2CoMnO6 can largely be attributed to strong metal-support interactions, as evidenced by a downshift in the binding energy of the Pt 4f bands, measured by X-ray photoelectron spectroscopy (XPS), which is often correlated not only with a downshift in the d-band center but also to a decreased adsorption of poisoning adsorbates. Moreover, when used as catalysts for the oxygen evolution reaction, Y2CoMnO6 displayed a much greater activity as compared with Y2NiMnO6. This behavior can largely be attributed not only to a preponderance of comparatively more favorable oxidation states and electronic configurations but also to the formation of an active layer on the surface of the Y2CoMnO6 catalyst, which collectively gives rise to improved performance metrics and greater stability as compared with both IrO2 and Y2NiMnO6. Overall, these results highlight the importance of both the chemical composition and the electronic structure of double perovskites, especially when utilized in multifunctional roles as either supports or catalysts.

Metal‐Organic Frameworks: Synthesis, Structures, and Applications

Metal‐Organic Frameworks: Synthesis, Structures, and Applications

Enhanced Electrocatalytic Oxidation of Small Organic Molecules on Platinum-Gold Nanowires: Influence of the Surface Structure and Pt-Pt/Pt-Au Pair Site Density.

The electrochemical oxidation of small organic molecules (SOMs) such as methanol and glucose is a critical process and has relevant applications in fuel cells and sensors. A key challenge in SOM oxidation is the poisoning of the surface by carbon monoxide (CO) and other partially oxidized intermediates, which is attributed to the presence of Pt-Pt pair sites. A promising pathway for overcoming this challenge is to develop catalysts that selectively oxidize SOMs via "direct" pathways that do not form CO as a primary intermediate. In this report, we utilize an ambient, template-based approach to prepare PtAu alloy nanowires with tunable compositions. X-ray photoelectron spectroscopy measurements reveal that the surface composition matches that of the bulk composition after synthesis. Monte Carlo method simulations of the surface structure of PtAu alloys with varying coverage of oxygen adsorbates and varying degrees of oxygen adsorption strength reveal that oxygen adsorption under electrochemical conditions enriches the surface with Pt and a large fraction of Pt-Pt sites remain on the surface even with the Au content of up to 50%. Electrochemical properties and the catalytic performance measurements of the PtAu nanowires for the oxidation of methanol and glucose reveal that the mechanistic pathways that produce CO are suppressed by the addition of relatively small quantities of Au (∼10%), and CO formation can be completely suppressed by 50% Au. The suppression of CO formation with small quantities of Au suggests that the presence of Pt-Au pair sites may be more important in determining the mechanism of SOM oxidation rather than Pt-Pt pair site density.

(Invited) Design and Synthesis of Nano-Porous / Nano-Structured Electrochemical Interfaces with Application in the Fuel Cell Catalysis

The drive toward efficient and durable fuel cells is founded on the design, synthesis, characterization, and testing of a variety of catalysts that in most cases include either Pt or Pd or a combination of both. Given the high cost and scarcity of these metals it is essential to either find a cost-effective alternative or to minimize as much as possible the amount of Pt / Pd in developed catalysts of interest. The route of amount minimization has been firstly approached by synthesizing catalysts in the form of nanoparticles. Nanoparticles are undoubtedly superior to other type of materials applicable in catalysis with their large surface area to volume ratio and unique physical and chemical properties. At the same time, they are also associated with some drawbacks like material loss during synthesis, surface contamination that is difficult to deal with, mechanical disconnection from the carrier electrode, and / or aggregation in time of exploitation. Such unwanted developments lead to a rapid reduction of the electrochemically active surface area (ECSA) and thus, to loss of activity and poor durability.A way to address these drawbacks is to employ electrochemical approaches for synthesizing the catalytically active layer directly on the carrier electrode. Such approach would not only provide for better adhesion and contamination free surface but would also enable a complete control over the amount of the deposited material along with its surface structure and composition thus reducing the overall synthetic cost. The electrochemical means normally include electrodeposition of a binary / ternary alloy layer with controlled thickness and elemental composition followed by a selective oxidative dissolution (de-alloying) of the less / least noble metal to create a continuous nanoporous film with tunable pore and ligament size in the single-digit nanometer range (1-4). Finally, as-synthesized film may either be employed directly as catalyst (3-7) or be subjected to an additional surface functionalization for boosting its activity and/or durability (1, 2, 8-10).This talk will introduce the use of electrochemical means in the design and synthesis of continuous nanoporous alloy catalysts based on Pt-(1, 9), Pd-(7, 10), and Au-(2, 6) with application in small organic molecule oxidation, oxygen reduction in alkaline media, and nitrate electroreduction reactions, respectively. The discussed synthetic approaches will include bulk alloy electrodeposition, electrochemical de-alloying, and electrochemical atomic layer deposition for sub-monolayer to a few layers surface functionalization. The presentation of each catalyst will include electrochemical and ultra-high vacuum-based characterization, followed by standard performance tests of the activity and durability of said catalysts in the respective applications. Finally, aspects of the catalysts’ performance along with hypothesized mechanistic views will be critically discussed in comparison with other nanoparticulate and/or nanostructured counterpart catalysts in the literature. References D. A. McCurry, M. Kamundi, M. Fayette, F. Wafula and N. Dimitrov, Acs Appl Mater Inter, 3, 4459 (2011).Y. Xie and N. Dimitrov, Acs Omega, 3, 17676 (2018).Y. Xie and N. Dimitrov, Appl Catal B-Environ, 263, 118366 (2020).Y. Xie, Y. Yang, D. A. Muller, H. D. Abruna, N. Dimitrov and J. Y. Fang, Acs Catal, 10, 9967 (2020).Y. Xie, C. Li, S. A. Razek, J. Y. Fang and N. Dimitrov, Chemelectrochem, 7, 569 (2020).H. Yang, J. X. Xia, L. Bromberg, N. Dimitrov and M. S. Whittingham, J Solid State Electr, 21, 463 (2017).Y. Xie, C. Li, E. Castillo, J. Fang and N. Dimitrov, Electrochimica Acta, 138306 (2021).L. Bromberg, M. Fayette, B. Martens, Z. P. Luo, Y. Wang, D. Xu, J. Zhang, J. Fang and N. Dimitrov, Electrocatalysis, 4, 24 (2013).J. X. Xia, I. Achari, S. Ambrozik and N. Dimitrov, Mater Res Bull, 85, 1 (2017).I. Achari and N. Dimitrov, Electrochem, 1, 4 (2020).

Killing Two Birds with One Stone: Selective Oxidation of Small Organic Molecule as Anodic Reaction to Boost CO2 Electrolysis

Replacing anodic oxygen evolution reaction (OER) with the oxidation of small organic molecules in CO2 electrolysis is an ingenious strategy to reduce the energy consumption while produce valuable anodic products instead of low‐value O2. Herein, an advanced CO2 electrolysis system constructed by replacing OER with selective methanol oxidation reaction (MOR) is reported as a proof‐of‐concept, which achieves the yielding of value‐added products in both cathode and anode. Notably, the MOR over a self‐supported NiCo‐based metal–organic framework‐derived anode (NiCo‐NF‐ET) only needs 1.291 V to reach a high current density of 100 mA cm−2, which is about 346 mV lower than that of OER. Simultaneously, formate can also be produced with the Faradaic efficiencies approaching to 100%. Consequently, in comparison with the conventional CO2 electrolysis system, integrating cathodic CO2 reduction reaction (CO2RR) with anodic MOR can lead to the reduction of about 880 mV to deliver the current density of 30 mA cm−2, while without compromising the selectivity of the products in both electrodes. Herein, the great potential to increase the economic benefits of CO2 electrolysis via the rational design of nonprecious electrocatalysts and participated anodic oxidation reactions is shown.

Rational Design of Single-Atom Site Electrocatalysts: From Theoretical Understandings to Practical Applications.

Atomically dispersed metal-based electrocatalysts have attracted increasing attention due to their nearly 100% atomic utilization and excellent catalytic performance. However, current fundamental comprehension and summaries to reveal the underlying relationship between single-atom site electrocatalysts (SACs) and corresponding catalytic application are rarely reported. Herein, the fundamental understandings and intrinsic mechanisms underlying SACs and corresponding electrocatalytic applications are systemically summarized. Different preparation strategies are presented to reveal the synthetic strategies with engineering the well-defined SACs on the basis of theoretical principle (size effect, metal-support interactions, electronic structure effect, and coordination environment effect). Then, an overview of the electrocatalytic applications is presented, including oxygen reduction reaction, hydrogen evolution reaction, oxygen evolution reaction, oxidation of small organic molecules, carbon dioxide reduction reaction, and nitrogen reduction reaction. The underlying structure-performance relationship between SACs and electrocatalytic reactions is also discussed in depth to expound the enhancement mechanisms. Finally, a summary is provided and a perspective supplied to demonstrate the current challenges and opportunities for rational designing, synthesizing, and modulating the advanced SACs toward electrocatalytic reactions.

Fabrication of polyaniline-supported bimetal AgNi nanoparticles and the enhanced performance towards formate oxidation

Bimetal nanocomposites display excellent electrocatalysis in the oxidation of small organic molecules. Herein, we demonstrated the successful synthesis of bimetal AgNi nanoparticles through a two-step method: an oxidant-induced in situ polymerization following a liquid phase reduction. The alloying AgNi nanoparticles with a diameter of 4–5 nm highly dispersed in the polyaniline matrix in a multi-particle way and formed a spherical nanocomposite AgNi@PANI. On this basis, we fabricated the AgNi@PANI-modified Pt electrode and studied its electrocatalysis for formate oxidation in acidic electrolytes. The results show that the alloying method is conducive to minimize the size of AgNi nanoparticles and keeps the metallic characters. PANI plays a crucial role in stabilizing and constraining the nanoparticles from dissipating into the electrolyte in the process of AgNi@PANI/Pt-catalyzing formate oxidation. A maximum oxidation peak current density of 30.7 mA cm-2 can be obtained when the molar ratio of silver to nickel is 1:0.5. In the chronoamperometry test, the current density of the fabricated electrode at 1200 s is nearly eight times higher than PANI/Pt.

Catalytic oxidation of small organic molecules by cold plasma in solution in the presence of molecular iron complexes\u2020

The plasma-mediated decomposition of volatile organic compounds has previously been investigated in the gas phase with metal oxides as heterogeneous catalysts. While the reactive species in plasma itself are well investigated, very little is known about the influence of metal catalysts in solution. Here, we present initial investigations on the time-dependent plasma-supported oxidation of benzyl alcohol, benzaldehyde and phenol in the presence of molecular iron complexes in solution. Products were identified by HPLC, ESI-MS, FT-IR, and ^{1}hbox {H NMR} spectroscopy. Compared to metal-free oxidation of the substrates, which is caused by reactive oxygen species and leads to a mixture of products, the metal-mediated reactions lead to one product cleanly, and faster than in the metal-free reactions. Most noteworthy, even catalytic amounts of metal complexes induce these clean transformations. The findings described here bear important implications for plasma-supported industrial waste transformations, as well as for plasma-mediated applications in biomedicine, given the fact that iron is the most abundant redox-active metal in the human body.

Acetol as a high-performance molecule for oxidation in alkaline direct liquid fuel cell

This work describes acetol as fuel for electrochemical oxidation in direct alkaline liquid fuel cells, in addition to electrochemical studies for acetol oxidation reactions (AOR) in alkaline medium, catalyzed by nanostructured palladium electrocatalysts supported on carbon (Pd/C). The AOR’s were evaluated by cyclic voltammetry and chronoamperometry and the results were similar those described in the literature for oxidation of small organic molecules, revealing evident oxidation peaks and chronoamperometric currents. Experiments were performed in an alkaline direct liquid fuel cell (ADLFC), using acetol as fuel and electrocatalysts of the Pd/C type as anode. The results in ADLFC showed high values of open circuit potential (OCP), obtaining 1341.3 mV, considerably higher than the results reported in the literature for ethanol oxidation, in addition to a promising power density, in the maximum result of 31.55 mW cm−2, presenting acetol as a high-performance molecule for oxidation in the ADLFC.