Complete Oxidation Of Ethanol Research Articles

2D PtRhPb Mesoporous Nanosheets with Surface-Clean Active Sites for Complete Ethanol Oxidation Electrocatalysis.

The development of active and selective metal electrocatalysts for complete ethanol oxidation reaction (EOR) into desired C1 products is extremely promising for practical application of direct ethanol fuel cells. Despite some encouraging achievements, their activity and selectivity remain unsatisfactory. In this work, it is reported that 2D PtRhPb mesoporous nanosheets (MNSs) with anisotropic structure and surface-clean metal siteperform perfectly for complete EOR electrocatalysis in both three-electrode and two-electrode systems. Different to the traditional routes, a selective etching strategy is developed to produce surface-clean mesopores while retaining parent anisotropy quasi-single-crystalline structure without the mesopore-forming surfactants. This method also allows the general synthesis of surface-clean mesoporous metals with other compositions and structures. When being performed for alkaline EOR electrocatalysis, the best PtRhPb MNSs deliver remarkably high activity (7.8 A mg-1) and superior C1 product selectivity (70% of Faradaic efficiency), both of which are much better than reported electrocatalysts. High performance is assigned to multiple structural and compositional synergies that not only stabilized key OHads intermediate by surface-clean mesopores but also separated the chemisorption of two carbons in ethanol by adjacent Pt and Rh sites, which facilitate the oxidation cleavage of stable C─C bond for complete EOR electrocatalysis.

The Effect of SnO<sub>2</sub> and Rh on Pt Nanowire Catalysts for Ethanol Oxidation

In this study, we synthesized Pt-Rh nanowires (NWs) through chemical reduction of metallic precursors using formic acid at room temperature, excluding the use of surfactants, templates, or stabilizing agents. These NWs were supported on two substrates: carbon (Vulcan XC-72R) and carbon modified with tin oxide (SnO<sub>2</sub>) via the sol-gel method (10 wt.% SnO<sub>2</sub>). We explored the electroactivity of Pt/SnO<sub>2</sub>/C, Pt-Rh/C, Pt-Rh/SnO<sub>2(commercial)</sub>/C (commercial SnO<sub>2</sub>), and Pt-Rh/SnO<sub>2</sub>/C NWs toward electrochemical oxidation of ethanol in acidic media using various techniques, including CO-stripping, cyclic voltammetry, derivative voltammetry, chronoamperometry, and steady-state polarization curves. Physical characterization involved X-ray diffraction and transmission electron microscopy. The synthesized NWs exhibit higher ethanol oxidation activity than the commercial Pt/C (Johnson Matthey™) catalyst. Rh atoms are hypothesized to enhance complete ethanol oxidation, while the NW morphology improves ethanol adsorption at the catalyst surface for subsequent oxidation. Additionally, the choice of support material plays a significant role in influencing the catalytic activity. The superior catalytic activity of Pt-Rh/SnO<sub>2</sub>/C NWs may be attributed to the facile dissociation of the C-C bond, low CO adsorption (electronic effect due to Rh presence), and the bifunctional mechanism facilitated by the oxophilic nature of the SnO<sub>2</sub> support.

RhCuBi Trimetallenes with Composition Segregation Coupled Crystalline‐Amorphous Heterostructure Toward Ethanol Electrooxidation

AbstractThe inefficiency of Pt and Pd benchmark catalysts in achieving complete ethanol oxidation, coupled with their inherent susceptibility to poisoning, poses a significant obstacle to the advancement of direct ethanol fuel cells. In this study, the development of self‐supported and ultrathin RhCuBi trimetallenes, demonstrating exceptional performance in ethanol electrooxidation through segregation and interface engineering is presented. The distinctive RhBi‐rich crystalline/RhCu‐rich amorphous heterostructure of RhCuBi trimetallenes creates a wealth of highly active interfacial sites for the ethanol oxidation reaction (EOR). This results in an impressive 43.3% Faradaic efficiency for the C1 pathway and a peak mass activity of 1.11 A mgRh−1 at 0.68 V versus reversible hydrogen electrode. Moreover, RhCuBi trimetallenes retain 60% of their initial mass activity after 8.5 h of constant potential electrolysis, outperforming commercial Pd and Pt catalysts (<3%). In/ex situ infrared spectroscopy directly reveals the generated C1 products and the key CH3CO* intermediates for EOR on RhCuBi trimetallenes. Theoretical calculations confirm that the RhBi alloy, particularly the lattice‐stretched crystalline/amorphous interfacial sites, facilitates the adsorption/activation of ethanol and the dehydrogenation of CH3CO* toward the C1 pathway of EOR. This breakthrough offers promising prospects for enhancing the efficiency and stability of ethanol electrooxidation in fuel cell applications.

Modeling interfacial electric fields and the ethanol oxidation reaction at electrode surfaces.

The electrochemical environment present at surfaces can have a large effect on intended applications. Such environments may occur, for instance, at battery or electrocatalyst surfaces. Solvent, co-adsorbates, and electrical field effects may strongly influence surface chemistry. Understanding these phenomena is an on-going area of research, especially in the realm of electrocatalysis. Herein, we modeled key steps in the ethanol oxidation reaction (EOR) over a common EOR catalyst, Rh(111), using density functional theory. We assessed how the presence of electrical fields may influence important C-C and C-H bond scission and C-O bond formation reactions with and without co-adsorbed water. We found that electric fields combined with the presence of water can significantly affect surface chemistry, including adsorption and reaction energies. Our results show that C-C scission (necessary for the complete oxidation of ethanol) is most likely through CHxCO adsorbates. With no electric field or solvent present C-C scission of CHCO has the lowest reaction energy and dominates the oxidation of ethanol. But when applying strong negative fields (with or without solvent), the C-C scission of CH2CO and CHCO becomes competitive. The current work provides insights into how electric fields and water solvent affect EOR, especially when simulated using density functional theory.

Composition engineering of carbon nanotubes supported PtxRhRu ultrafine nanocatalysts for ethanol electro-oxidation: Elucidating the role of trimetallic sites

The practice of direct ethanol fuel cells (DEFCs) is hindered by insufficient activity of anode Pt-based catalyst for ethanol oxidation reaction (EOR), while alloying Rh and Ru to Pt is hopeful to solve the problem by simultaneously enhancing CC cleavage and decreasing poisoning; and Ru owning better stability and activity than usually doped Sn in alkaline electrolyte. Nevertheless, Pt-Rh-Ru catalysts were rarely reported. In this work, to avoid random trials, the “composition engineering” strategy was applied to design PtxRhRu catalysts. The optimal x range was predicted by DFT. Then, carbon nanotubes supported PtxRhRu ultrafine nanoparticles (PtxRhRu/CNTs) were synthesized and characterized. The synthetic mechanism was also studied. EOR tests show that, in line with the forecast, Pt4RhRu/CNTs (∼1.9 nm) exhibit the highest activity (5.85 mA·cm−2), 6.97 times of commercial Pt/C, and higher than most reports. The selectivity, stability and durability are also excellent. DFT analysis reveals the role of Pt-Rh-Ru site for the first time, that the optimal route on PtxRhRu is changed. New route clearly enhances complete ethanol oxidation and reduces poisoning. Bifunctional mechanism on Pt-Rh-Ru site was also confirmed. This study may provide new perspective for material design; the products are also promotive for DEFCs into practice.

Electronic and Geometric Effects Endow PtRh Jagged Nanowires with Superior Ethanol Oxidation Catalysis.

Complete ethanol oxidation reaction (EOR) in C1 pathway with 12 transferred electrons is highly desirable yet challenging in direct ethanol fuel cells. Herein, PtRh jagged nanowires synthesized via a simple wet-chemical approach exhibit exceptional EOR mass activity of 1.63 A mgPt-1 and specific activity of 4.07mA cm-2 , 3.62-fold and 4.28-folds increments relative to Pt/C, respectively. High proportions of 69.33% and 73.42% of initial activity are also retained after chronoamperometric test (80000 s) and 1500 consecutive potential cycles, respectively. More importantly, it is found that PtRh jagged nanowires possess superb anti-CO poisoning capability. Combining X-ray absorption spectroscopy, X-ray photoelectron spectroscopy as well as density functional theory calculations unveil that the remarkable catalytic activity and CO tolerance stem from both the Rh-induced electronic effect and geometric effect (manifested by shortened Pt─Pt bond length and shrinkage of lattice constants), which facilitates EOR catalysis in C1 pathway and improves reaction kinetics by reducing energy barriers of rate-determining steps (such as *CO → *COOH). The C1 pathway efficiency of PtRh jagged nanowires is further verified by the high intensity of CO2 relative to CH3 COOH/CH3 CHO in infrared reflection absorption spectroscopy.

Self-Interface in Rh Nanosheets-Supported Tetrahedral Rh Nanocrystals for Promoting Electrocatalytic Oxidation of Ethanol.

Direct ethanol fuel cells hold great promise as a power source. However, their commercialization is limited by anode catalysts with insufficient selectivity toward a complete oxidation of ethanol for a high energy density, as well as sluggish catalytic kinetics and low stability. To optimize the catalytic performance, rationally tuning surface structure or interface structure is highly desired. Herein, a facile route is reported to the synthesis of Rh nanosheets-supported tetrahedral Rh nanocrystals (Rh THs/NSs), which possess self-supporting homogeneous interface between Rh tetrahedrons and Rh nanosheets. Due to full leverage of the structural advantages within the given structure and construction of interfaces, the Rh THs/NSs can serve as highly active electro-catalysts with excellent mass activity and selectivity toward ethanol electro-oxidation. The in situ Fourier transform infrared reflection spectroscopy showed the Rh THs/NSs exhibit the highest C1 pathway selectivity of 23.2%, far exceeding that of Rh nanotetrahedra and Rh nanosheets. Density function theory calculations further demonstrated that self-interface between Rh nanosheets and tetrahedra is beneficial for C-C bond cleavage of ethanol. Meanwhile, the self-supporting of 2D nanosheets greatly enhance the stability of tetrahedra, which improves the catalytic stability.

The nature of local oxygen radical boosts electrocatalytic ethanol to selectively generate CO2

Developing a high-activity and antitoxic electrocatalyst is still a demanding task. Enhancing the enrichment of oxygen species on catalysts is beneficial for thorough oxidation of ethanol to generate CO2, but the role of oxygen radicals in the process of ethanol oxidation is still ambiguous. Herein, an artificial oxidase that can catalyze oxygen to generate reactive oxygen species (ROS) in-situ has been applied in EOR for the first time and the roles of •OH, •O2−, and 1O2 in complete oxidation of ethanol were investigated. The mass activity of EOR is 18.2 A mgPt−1 in 1 mol L−1 KOH and the CO2 selectivity is 98.7%. The research showed that Sn element could optimize coordination mode on catalyst surface, which enhanced oxidase activity of the catalyst. Explored the intermediates of the reaction and evaluated the performance of the catalyst using in-situ infrared testing technology. Theoretical calculations indicate that C–C bond breakage of *CH3CO to generate *CH3 and *CO is potential determination steps in the C1 pathway. When singlet oxygen is present on the PtSn IM/C surface, the dissociation energy of C–C bond is –0.51 eV, which is lower than the 1.07 eV of hydroxyl radicals and –0.47 eV of superoxide anions.

Confinement Effects of Hollow Structured Pt-Rh Electrocatalysts toward Complete Ethanol Electrooxidation.

In the anodic ethanol oxidation reaction (EOR) for direct ethanol fuel cells, the coverage of hydroxide (OHads) is a major adsorbent competing with C-C bond cleavage, which is necessary for complete ethanol oxidation (C1-pathway) and durability. Beyond utilizing a less-alkaline electrolyte that causes ohmic losses, an alternative strategy to optimize OHads coverage is to intentionally exploit local pH changes near the electrocatalyst surface that are governed by a combination of released H+ during EOR and OH- mass transport from the bulk solution. Here, we manipulate the local pH swing by fine-tuning the electrode porosity with Pt1-xRhx hollow sphere electrocatalysts based on particle size (250 and 350 nm) and mass loading. With the smaller size of 250 nm, Pt0.5Rh0.5 (∼50 μg cm-2) shows a high activity of 1629 A gPtRh-1 (2488 A gPt-1) in a 0.5 M KOH-containing electrolyte, which is ∼50% higher than the most active binary catalysts to date. Moreover, a higher C1-pathway Faradaic efficiency (FE) of 38.3% and 80% longer durability are achieved with a 2-fold increase in mass loading. In the more porous electrodes, a local acidic environment created by hindered OH- mass transport better optimizes OHads coverage, providing more active sites for the desired C1-pathway and a continuous EOR.

Efficient Oxidation of Ethanol at Ru@Pt Core-Shell Catalysts in a Proton Exchange Membrane Electrolysis Cell

Efficient electrochemical oxidation of ethanol in fuel cells and electrolysis cells is important for generating power and hydrogen, respectively, from renewable resources. PtRu alloys are most widely employed as catalysts because they provide high activities at low potentials. However, they produce acetic acid as the main product from ethanol, which results in low faradaic and overall efficiencies. In contrast, Pt provides high selectivity for the complete oxidation of ethanol to CO2, but low activities. Ru@Pt core–shell nanoparticles can improve efficiency by delivering higher activity than Pt and enhanced formation of CO2 relative to PtRu. Here, Ru@Pt catalysts have been prepared by depositing Pt onto a commercial carbon-supported Ru catalyst. The influence of the amount of Pt deposited has been investigated in H2SO4(aq) at ambient temperature and in a proton exchange membrane cell at 80 °C. Activities for ethanol oxidation were intermediate between those for commercial Pt and PtRu catalysts, providing higher currents than Pt at low potentials, and higher currents than PtRu at high potentials. Faradaic yields of CO2 (38%–48%) were greatly increased relative to the PtRu alloy catalyst (11%). This will optimize the efficiency of ethanol oxidation in PEM electrolysis and fuel cells.

Role of ZSM-5/AC hybrid support on the catalytic activity of Pd-Ag electrocatalysts towards ethanol oxidation: An experimental and kinetic study

Ethanol is a promising future fuel for Direct Alcohol Fuel Cells (DAFCs) and one of the significant half-cell reactions of this type of FC is ethanol oxidation reaction (EOR). However, the high cost, low selectivity of the catalyst towards complete oxidation of ethanol to CO2, and poor electrode kinetics are the key challenges in commercializing this technology. The way to mitigate these issues is to design affordable, stable, and highly efficient electrocatalysts. In this prospect, we developed a zeolite-carbon (ZSM-5/AC) supported Pd-Ag binary alloy catalysts via a simple co-impregnation followed by co-reduction method. The influence of ZSM-5/AC composite support and its composition on the activity of bimetallic Pd-Ag catalyst has been studied in detail. The PdAg/ZSM-5/AC electrocatalyst with 1:3 wt ratio of ZSM-5:AC exhibited better catalytic performance (10.9 mA cm−2) and tolerance towards intermediate species than PdAg/AC and Pd/AC electrocatalysts. The larger jf/jb (forward to backward current density ratio) of 2.8 for PdAg/ZSM-5/AC indicates lower carbonaceous species accumulation on the zeolite-modified electrode. Additionally, the material possessed a good long-term cyclic stability up to 500 cycles. The high activity observed for PdAg/ZSM-5/AC could be attributed to synergism between bimetallic catalysts and high surface area zeolite support. Overall, the study reveals that the Pd-Ag bimetallic and ZSM-5/AC are potentially efficient electrocatalyst and support, respectively, for the ethanol oxidation reaction in DEFC application.

Interface synergism and engineering of Pd/Co@N-C for direct ethanol fuel cells

Direct ethanol fuel cells have been widely investigated as nontoxic and low-corrosive energy conversion devices with high energy and power densities. It is still challenging to develop high-activity and durable catalysts for a complete ethanol oxidation reaction on the anode and accelerated oxygen reduction reaction on the cathode. The materials’ physics and chemistry at the catalytic interface play a vital role in determining the overall performance of the catalysts. Herein, we propose a Pd/Co@N-C catalyst that can be used as a model system to study the synergism and engineering at the solid-solid interface. Particularly, the transformation of amorphous carbon to highly graphitic carbon promoted by cobalt nanoparticles helps achieve the spatial confinement effect, which prevents structural degradation of the catalysts. The strong catalyst-support and electronic effects at the interface between palladium and Co@N-C endow the electron-deficient state of palladium, which enhances the electron transfer and improved activity/durability. The Pd/Co@N-C delivers a maximum power density of 438 mW cm−2 in direct ethanol fuel cells and can be operated stably for more than 1000 hours. This work presents a strategy for the ingenious catalyst structural design that will promote the development of fuel cells and other sustainable energy-related technologies.

Study on ethanol electro-oxidation over a carbon-supported Pt-Cu alloy catalyst by pinhole on-line electrochemical mass spectrometry.

A carbon supported Pt-Cu electrocatalyst was synthesized by the microwave-polyol method following acid-treatment and physically characterized by different techniques including X-ray diffraction (XRD) and transmission electron microscopy (TEM). Both potentiodynamic and potentiostatic measurements with pinhole on-line electrochemical mass spectrometry were carried out to study the electrocatalytic activity and reaction intermediates of Pt/C and Pt-Cu/C electrocatalysts during the ethanol oxidation reaction. The results of potentiodynamic and potentiostatic measurements showed that the Pt-Cu/C electrocatalyst has higher ethanol oxidation efficiency and incomplete ethanol oxidation to acetaldehyde and acetic acid prevails under the given conditions. After calibration of the m/z = 44 mass signal, the CO2 current efficiencies on Pt/C and PtCu-3/C were ∼7% and ∼12%, respectively, which reveal that the presence of copper enhances the complete ethanol oxidation to CO2.

Activity Enhancement of PtIr Catalysts for Complete Ethanol Oxidation Reaction by Tuning C–O Coupling Abilities

Designing efficient catalysts for the complete ethanol oxidation reaction (EOR) remains challenging because of its complex reaction network, which involves more than 70 reactions of C2 species, many reactions of C1 species, water dissociation, as well as reactions leading to by-products. Recently, the promising EOR performance of the one-atom-thick Ir-rich skin of a bimetallic PtIr electrocatalyst was illustrated and its further improvement requires a thorough understanding of the complete EOR mechanism that is still largely lacking. Therefore, we studied 58 critical elementary reactions of complete EOR including all three stages of catalysis of ethanol oxidation, i.e., dehydrogenation, C–C bond cleavage, and CO2 formation, as well as including water dissociation, on three (100)-exposed layered bimetallic Pt–Ir catalysts using density functional theory (DFT) calculations. Based on the activation and reaction energies, we mapped out the mechanisms of complete EOR on these layered PtIr catalysts. The DFT results demonstrated that the different C–O coupling abilities of the catalyst plays a leading role in the complete EOR performance of Pt–Ir catalysts. We further performed DFT studies on the reactions on a Ir@Pt(100) surface with about 6% Pt atoms on the Ir layer. The surface Pt atoms exhibit excellent C–O coupling of C1 species (e.g., CO + O → CO2), while the Ir atoms prevent the C–OH coupling to form CH3COOH (CH3CO + OH → CH3COOH). Both DFT and kinetics studies indicate that the Ir@Pt(100) surface with Pt-doped active sites is the best for complete EOR and is responsible for the experimentally observed high catalytic performance. This work indicates effective EOR catalysis need to go beyond single metal catalysts and the core–shell structures of multimetallic catalysts.

Pt Atomic Layers with Tensile Strain and Rich Defects Boost Ethanol Electrooxidation.

Surface and strain engineering are two effective strategies to improve performance; however, synergetic controls of surface and strain effects remains a grand challenge. Herein, we report a highly efficient and stable electrocatalyst with defect-rich Pt atomic layers coating an ordered Pt3Sn intermetallic core. Pt atomic layers enable the generation of 4.4% tensile strain along the [001] direction. Benefiting from synergetic controls of surface and strain engineering, Pt atomic-layer catalyst (Ptatomic-layer) achieves a remarkable enhancement on ethanol electrooxidation performance with excellent specific activity of 5.83 mA cm-2 and mass activity of 1166.6 mA mg Pt-1, which is 10.6 and 3.6 times higher than the commercial Pt/C, respectively. Moreover, the intermetallic core endows Ptatomic-layer with outstanding durability. In situ infrared reflection-absorption spectroscopy as well as density functional theory calculations reveal that tensile strain and rich defects of Ptatomci-layer facilitate to break C-C bond for complete ethanol oxidation for enhanced performance.

Rhodium decorated stable platinum nickel nanowires for effective ethanol oxidation reaction

Direct ethanol fuel cells (DEFCs) are considered one of the most promising energy resources for portable power devices. The current mainstream catalysts used for DEFCs are Pt- or Pd-based, which facilitate the partial oxidation of ethanol to CH3CHO or CH3COOH, but not the C—C bond cleavage, which is the inevitable path for the complete oxidation of ethanol. In addition, most noble catalysts are easily poisoned by CO, shortening their lifespan and stability, thus inhibiting the practical application of the catalysts. Herein, we report a type of ultrathin trimetallic Pt/Ni/Rh nanowires with various Rh contents toward the ethanol oxidation reaction (EOR), and the optimized Pt6Ni2Rh3/C demonstrates a high mass activity of 1.16 A mgPt−1 as well as considerable stability, anti-CO poisoning ability, and complete ethanol oxidation selectivity. In addition, density functional theory calculations reveal that introducing Rh to bimetallic Pt/Ni endows the catalyst with a moderate intermediate adsorption capacity and enhanced C—C bond cleavage capacity, favorable for the complete oxidation of ethanol.

Tuning the Selective Ethanol Oxidation on Tensile-Trained Pt(110) Surface by Ir Single Atoms.

Development of efficient and robust electrocatalysts for complete oxidation of ethanol is critical for the commercialization of direct ethanol fuel cells. However, the complete oxidation of ethanol suffers from poor efficiency due to the low C1 pathway selectivity. Herein, single-atomic Ir (Ir1 ) on hcp-PtPb/fcc-Pt core-shell hexagonal nanoplates (PtPb@PtIr1 HNPs) enclosed by Pt(110) surface with a 7.2% tensile strain is constructed to drive complete electro-oxidation of ethanol. Benefiting from the construction of Ir1 sites, the PtPb@PtIr1 HNPs exhibit a Faraday efficiency of 57.93% for the C1 pathway, which is ≈8.3 times higher than that of the commercial Pt/C-JM. Furthermore, the PtPb@PtIr1 HNPs show a top-ranked electro-activity achieving 45.1-fold and 56.3-fold higher than the specific and mass activities of Pt/C-JM, respectively. Meanwhile, the durability can be significantly enhanced by the construction of Ir1 sites. Density functional theory calculations indicate that the strong synergy on the PtPb@PtIr1 HNPs surface significantly promotes the breaking of CC bond of CH2 CO* and facilitates CO oxidation and suppresses the deactivation of the catalyst. This work offers a unique single-atom approach using low-coordination active sites on shape-controlled nanocrystals to tune the selectivity and activity toward complicated catalytic reactions.

Gold–rhodium nanoflowers for the plasmon enhanced ethanol electrooxidation under visible light for tuning the activity and selectivity

Direct ethanol fuel cells (DEFCs) are a promising power source, but the low selectivity to ethanol complete oxidation is still challenging. The localized surface plasmon resonance (LSPR) excitation has been reported to accelerate and drive several chemical reactions, including the ethanol oxidation reaction (EOR), coming as a strategy to improve catalysts performance. Nonetheless, metallic nanoparticles (NPs) that present the LSPR excitation in the visible range are known for leading to the incomplete oxidation of ethanol. Thus, we report here the application of gold-rhodium nanoflowers (Au@Rh NFs) towards the plasmon-enhanced EOR. These hybrid materials consist of a Au spherical nucleus covered by Rh branches shell, combining plasmonic and catalytic properties. Firstly, the Au@Rh NFs metallic ratio was investigated in dark conditions to obtain an optimal catalyst. Experiments were also performed under light irradiation. Our data demonstrated an improvement of 352% in current density and 36% in selectivity to complete ethanol oxidation under 533 nm laser incidence. Moreover, the current density showed a linear increase with the laser power density, indicating a photochemical effect and thus enhancement due to the LSPR properties.

Local Silver Site Temperature Critically Reflected Partial and Complete Photooxidation of Ethanol Using Ag–TiO2 as Revealed by Extended X-ray Absorption Fine Structure Debye–Waller Factor

The critical factors in choosing the reaction pathway for photocatalysis are often unclear. In this study, for a typical Ag–TiO2 photocatalyst, the control factors of partial and complete oxidation of ethanol were investigated using kinetics, UV–visible and emission spectroscopy, and silver K-edge extended X-ray absorption fine structure. Low concentrations of O2-derived intermediate species that were not detected by curve-fitting analysis could be monitored under the photocatalytic conditions based on the local temperature of Ag sites provided by the Debye–Waller factor and the correlated Debye model. The site temperature monitoring was extended to Ag nanoparticles growing from 0.5 to 3.6 nm under photocatalytic reaction conditions. The Ag site temperature reached 404 K under reductive conditions to dehydrogenate ethanol into acetaldehyde, whereas it was 363–368 K under oxidative conditions owing to O2-derived species forming CO2, CH4, and H2O to suppress localized surface plasmon resonance. Under UV light, partial ethanol oxidation to acetaldehyde and O2 activation for complete oxidation to CO2 and H2O proceeded over TiO2. However, under visible light, the C–C bond cleavage to CO2 and CH4 and complete oxidation to CO2 and H2O combined with the O2-derived species transferred from the TiO2 surface proceeded over Ag0 nanoparticles.

Unveiling Complete Ethanol Oxidation through a Hybrid Enzymatic and Organic Catalyst Cascade in an Electrochemical Micro-Reactor Device

Biological fuel cells have been extensively reported as a efficient and sustainable device to convert chemical energy to electrical energy [1]. Biofuel cells (BFCs) are alternative energy sources which use enzymes (enzymatic biofuel cell) or microorganisms (microbial fuel cell) as the electrocatalysts instead of the traditional noble metal catalysts. Ethanol is a fuel that can be used in combined enzymatic fuel cell due to its high energy density (8.03 kW h kg -1), low emission, and storage security [2]. The advantage of enzymes is that they exhibit high specificity and turnover rate, however, mimicking the natural metabolism from ethanol through electrometabolic pathways is enormously difficult. To overcome the limitations of using multiple enzymes to achieve the complete ethanol oxidation, a small molecule organic catalyst can be employed. TEMPO (2,2,6,6-tetramethylpiperidin-1-yl) oxyl) is a small organic catalyst that does not present limited substrate specificity such as enzymes face, due to its ability to oxidize oxygen, nitrogen and sulfur-containing functional groups. Thus, hybrid system enables improvement at the rate of electrocatalytic oxidation of several biofuels [2 - 4]. Herein, we described the development of a hybrid catalytic architecture combining an organic oxidation catalyst, 4-amino-TEMPO (TEMPO-NH2), and a recombinant enzyme, oxalate decarboxylase (OxDc) to catalyze complete ethanol electrooxidation. The catalyst system was coupled with a novel small scale electrolysis cell utilizing polycaprolactone (PCL) and carbon composite electrodes for bulk electrolysis. Electrochemical meansurements and product detection by nuclear magnetic resonance (NMR) after 12 hours of electrolysis have shown for the first time that an organic catalyst and decarboxylase enzyme enhances the overall steps in the cascade operating at acidic pH enabling enhanced electrochemical oxidation of ethanol to CO2. To validate the reaction sequence, a novel micro-reactor device enabled low-cost product analysis and allows for high analyte sensitivity. Overall, this work demonstrated that bi-cascade of TEMPO-NH2 and OxDc can be combined in an electrochemical cell to synergistically catalyze the oxidation of substrates that make up the steps of the ethanol oxidation cascade and is promising for a wide array of applications, including biosensors, environmental monitoring, and biofuel cells.