Catalyst For Reduction Research Articles

A bioinspired Fe/Mo bimetallic nitride catalyst for efficient electrochemical ammonia synthesis and Zn-nitrate battery

The electrocatalytic nitrate reduction reaction to ammonia (NRA) offers a promising alternative to traditional ammonia synthesis methods. In nature, enzymes containing molybdenum and iron sites catalyze the reduction of nitrate and nitrite ions. Drawing inspiration from these enzymes, we synthesized a carbon-coated nano-octahedra of FeMo-based nitride (FeMoN@C NO) by pyrolyzing phosphomolybdic acid hydrate (POM) doped Fe-NH2-MIL-101 to catalyze NRA. Experimental results demonstrate that in an alkaline environment, FeMoN@C NO exhibits a suitable hydrogen evolution reaction (HER) capacity, and the protons or hydroxyls produced effectively facilitate the hydrogenation reaction in the ammonia synthesis process. Additionally, the introduction of Mo increases the number of active sites and effectively reduces the thermodynamic barrier in NRA, thereby enhancing the rate of ammonia synthesis. As a result, FeMoN@C NO displays outstanding NH3 Faradaic efficiency (FE) of 98.2 % and an NH3 yield of 434.16 µmol/h cm−2. Building upon the excellent electrocatalytic properties of FeMoN@C NO, a new Zn-nitrate battery system is assembled in this work, which exhibits an outstanding peak power density of 3.23 mW cm−2 and an FE of 91.58 % for NH3 production. This work provides a new perspective for designing enzyme-mimicking nitrate reduction catalysts and broadens the application of Zn-based batteries.

Catalytic development of boron and sulphur-doped g-C3N4 supported Cu-MOF composite for nitroarenes reduction reaction

Todays, the mesoporous heteroatom-doped materials were attracted the scientist interest due to their outstanding properties such as thermal/chemical stability, high specific surface area (SSA), facile synthetic protocol and also abundance precursor. So, in this study, the advanced and applicable Boron and Sulphur-doped g-C3N4 (g-BSCN) supported Cu-MOF (Cu@g-BSCN) was prepared via in situ growth of Cu-MOF on the surface of g-BSCN using H3BO3, thiourea, Cu(NO3)2. 3H2O, and Terephthalic acid. The synergistic effect of B and S as the heteroatoms was triggered the plenty activated sites owing to the structural defect on the surface of the mesoporous g-BSCN. Moreover, the catalytic efficiency of g-BSCN was improved by in situ formation of copper-based MOF. The synthesized Cu@g-BSCN composite was utilized as the competent heterogenous catalyst in nitroarenes reduction in green and mild reaction condition (green solvent, and ambient temperature). High catalytic performance and desired recoverability are some of the benefits of this catalytic system.

Review on polyaniline-based nanocomposite heterogeneous catalysts for catalytic reduction of hazardous water pollutants.

Water contamination by highly toxic substances has generated serious ecological disturbances and health problems for humans. Hence, decontamination of toxic pollutants using advanced, inexpensive, and eco-friendly approaches is the current demand. Heterogeneous catalyst-based catalytic reduction processes have offered the opportunity to transform hazardous water pollutants into non-hazardous products via sustainable, eco-friendly, and efficient routes and might be a competitive substitute for existing traditional water purification techniques. However, the key challenges linked with pure heterogeneous catalysts include agglomeration and poor dispersion, stability, recovery, and reusability, which result in poor activity and efficiency. Thus, it is essential to produce multipurpose polymer-based composite catalysts using conducting polymers, which are exceptionally good supportive and matrix materials. The blending of metal-based nanomaterials with polyaniline conducting polymers produces highly stable and efficient heterogeneous nanocomposite catalysts with amazing catalytic activity against a wide range of water pollutants. The heterogeneous catalytic reductive degradation of immensely toxic pollutant water has gained substantial curiosity because of its excellent physicochemical and surface characteristics, porous structure, recoverability, and recyclability. Therefore, this review presents the latest efforts to generate various polyaniline-based nanocomposite catalysts using a polyaniline matrix and various nanofiller materials and their potential applications in heterogeneous catalytic reduction degradation of water pollutants.

Theoretical Study on the Electrocatalytic CO2 Reduction Mechanism of Single-Atom Co Complexed Carbon-Based (Co-Nχ@C) Catalysts Supported on Carbon Nanotubes.

Electrocatalytic CO2 reduction serves as an effective strategy to tackle energy crises and mitigate greenhouse gas effects. The development of efficient and cost-effective electrocatalysts has been a research hotspot in the field. In this study, we designed four Co-doped single-atom catalysts (Co-Nχ@C) using carbon nanotubes as carriers, these catalysts included tri- and dicoordinated N-doped carbon nanoribbons, as well as tri- and dicoordinated N-doped graphene, respectively denoted as H3(H2)-Co/CNT and 3(2)-Co/CNT. The stable configurations of these Co-Nχ@C catalysts were optimized using the PBE+D3 method. Additionally, we explored the reaction mechanisms of these catalysts for the electrocatalytic reduction of CO2 into four C1 products, including CO, HCOOH, CH3OH and CH4, in detail. Upon comparing the limiting potentials (UL) across the Co-Nχ@C catalysts, the activity sequence for the electrocatalytic reduction of CO2 was H2-Co/CNT > 3-Co/CNT > H3-Co/CNT > 2-Co/CNT. Meanwhile, our investigation of the hydrogen evolution reaction (HER) with four catalysts elucidated the influence of acidic conditions on the electrocatalytic CO2 reduction process. Specifically, controlling the acidity of the solution was crucial when using the H3-Co/CNT and H2-Co/CNT catalysts, while the 3-Co/CNT and 2-Co/CNT catalysts were almost unaffected by the solution's acidity. We hope that our research will provide a theoretical foundation for designing more effective CO2 reduction electrocatalysts.

Recent advances in carbon-based catalysts for electrocatalytic nitrate reduction to ammonia

Recent advances in carbon-based catalysts for electrocatalytic nitrate reduction to ammonia

New mechanistic insights into CO2 electroreduction to methane on penta-octa-graphene catalyst

Electrocatalytic reduction of CO2 to produce high value-added products is an important way to achieve sustainable production of green energy, but it is limited by high complexity of the catalyst structure and reaction process, making the rational design of the catalyst and the targeted generation of specific products a huge challenge. Herein, based on the penta-octa-graphene (POG) with sp2 and sp3 hybrid as the prototype, we theoretically guide the design of CO2 electrocatalytic reduction (CO2RR) catalyst over pure POG and TM doping POG (TM@POG). Our mechanistic study highlights two key factors in new pathway for CH4 production and catalytic performance, i.e., TM provides electron transfer for the key intermediate *CHO, promoting the activation of CO2, and the type of protonation for CO2RR is determined by the charge accumulation on the O atom of the intermediates. This reduces the complexity of the reaction and provides a predictive effect on the formation of intermediates. More importantly, the proper values of the Gibbs free energy indicate that TM@POG is an ideal catalyst candidate, especially the Fe@POG, which is superior to Cu (211) material. On this basis, three simple descriptors (Bader charge, d-band center εd and descriptor φ) based on the inherent properties of atoms were constructed to reveal the underlying causes of the improvement of catalytic activity. Our results provide a new understanding of the ’structure-performance’ relationship of carbon-based electrocatalysts, thus providing a useful strategy for the design of catalysts for CO2RR.

New metallophthalocyanine (M: Ni(II) and Fe(II)) complexes as efficient catalysts for transfer hydrogenation of various ketones

Hydrogen transfer reduction methods are attracting increasing attention from synthetic chemists in view of their operational simplicity. Therefore, the novel Ni(II) and Fe(II) tetra substituted metallophthalocyanines containing resorcinol and guaiacol groups were synthesized using microwave irradiation and characterized via elemental analysis, UV-Vis and FT-IR spectroscopy, and TGA. The comparison of the catalytic features of phthalocyanine based on metals is discussed in detail. These phthalocyanine-complexes were tested in transfer hydrogenation (TH) of ketones in the existence of KOH, utilizing 2-propanol as a hydrogen source. Examination of different carbonyl substrates revealed that Nickel (II) phthalocyanine, (Ni2) complex was a remarkable catalyst for the catalytic reduction of acetophenones (1.0 mol % of catalyst, 99 % conversion). Furthermore, we have discovered that the catalytic characteristics of this class of molecules are significantly influenced by both steric and electronic variables.

Sludge Recycling from Non-Lime Purification of Electrolysis Wastewater: Bridge from Contaminant Removal to Waste-Derived NOX SCR Catalyst

Catalysts for the selective catalytic reduction (NOX SCR) of nitrogen oxides can be obtained from sludge in industrial waste treatment, and, due to the complex composition of sludge, NOX SCR shows various SCR efficiencies. In the current work, an SCR catalyst developed from the sludge produced with Fe/C micro-electrolysis Fenton technology (MEF) in wastewater treatment was investigated, taking into account various sludge compositions, Fe/C ratios, and contaminant contents. It was found that, at about 300 °C, the NOX removal rate could reach 100% and there was a wide decomposition temperature zone. The effect of individual components of electroplating sludge, i.e., P, Fe and Ni, on NOX degradation performance of the obtained solids was investigated. It was found that the best effect was achieved when the Fe/P was 8/3 wt%, and variations in the Ni content had a limited effect on the NOX degradation performance. When the Fe/C was 1:2 and the Fe/C/P was 1:2:0.4, the electroplating sludge formed after treatment with Fe/C MEF provided the best NOX removal rate at 100%. Moreover, the characterization results show that the activated carbon was also involved in the catalytic reduction degradation of NOX. An excessive Fe content may cause agglomeration on the catalyst surface and thus affect the catalytic efficiency. The addition of P effectively reduces the catalytic reaction temperature, and the formation of phosphate promotes the generation of adsorbed oxygen, which in turn contributes to improvements in catalytic efficiency. Therefore, our work suggests that controlling the composition in the sludge is an efficient way to modulate SCR catalysis, providing a bridge from contaminant-bearing waste to efficient catalyst.

Single-, double-, and triple-atom catalysts on PC6 for nitrate reduction to ammonia: A computational screening

Single-atom catalysts (SACs) exhibit higher atomic utilization, while double-atom catalysts (DACs) and triple-atom catalysts (TACs) have an advantage due to the synergistic effect of multiple atomic centers. However, the current research on the mechanism of multiple-atom catalysts in electrocatalytic nitrate reduction to ammonia (NRA) remains insufficient. Herein, we investigated a series of homonuclear single-, double-, and triple-atom catalysts on carbon phosphide (PC6) monolayers (TMn@PC6, where TM = non-noble transition metals; n = 1, 2, or 3). The NRA activity of these catalysts was assessed by the density functional theory calculations, Co3@PC6 and Ru3@PC6 exhibit superior limiting potentials of −0.34 V and −0.36 V, respectively. Their capability to produce *H with optimal free energy on their surface enhances the electrochemical potential-determining step of *NO to *NOH while simultaneously inhibiting the hydrogen evolution reaction. The movement of the d-band center, induced by metal atom doping, regulates the adsorption strength of *NO, thus achieving a lower barrier for the hydrogenation step. This work provides theoretical guidance for the development of highly efficient multiple-atom catalysts for NRA.

Functional Ni/MnO2 heterostructure electrocatalysts based on self-sacrifice-induced LDHs anchored on nanofibers for microbial fuel cells

Designing cost-effective, highly active oxygen reduction catalysts for high-power-density microbial fuel cells (MFCs) is a significant challenge. To address this, this study uniformly dispersed layered double hydroxides (LDHs) on nanofiber surfaces, and subsequently utilized the self-sacrifice method of zeolite imidazole frameworks (ZIFs) to synthesize LDH/ZIF@CNFs bimetallic heterostructure with precise lattice matching. Experimental results collectively verified that LDH/ZIF@CNFs-12 exhibits an onset potential of -0.087 V, surpassing Pt/C (-0.098 V). Impressively, MFC equipped with LDH/ZIF@CNFs-12 achieves a high power density of 939.05 mW/cm2, surpassing Pt/C (859.74 mW/cm2). The excellent electrocatalytic performance of this catalyst originates from the rich active sites exposed in the LDHs core during the MOFs-assisted synthesis process, and the synergistic catalysis achieved by the formation of heterojunctions. In addition, 3D nanofibers uniformly disperse active sites and reduce large band gaps. This work unveils a new perspective for cost-effective, eco-friendly, and sustainable catalysts suitable for MFCs.

The cooperative p-n heterojunction and Schottky junction in Au-decorated hierarchical CuS@SnS2 hollow cubes for boosted charge transport and CO2 photoreduction

During the photocatalytic CO2 reduction process, fast charge transport, abundant active sites, and high visible light utilization in photocatalysts are key to achieving excellent CO2 conversion efficiency. In this work, we have designed and prepared hierarchical CuS@SnS2p-n heterostructure hollow cubes for photocatalytic CO2 reduction. First, a monolayer of CuS was in situ generated on the pre-prepared Cu2O cubes to construct core–shell Cu2O@CuS cubes by sulfidation of Cu2O cubes. The following etching process led to the formation of CuS hollow cubes. Finally, the hierarchical CuS@SnS2p-n heterostructure hollow cubes were obtained by growing SnS2 nanosheets on the CuS hollow cubes. The prepared CuS@SnS2p-n heterostructure hollow cubes showed an improved photocatalytic CO2 reduction activity compared with the bare CuS and SnS2 control samples. The p-n heterojunction formed between SnS2 and CuS as well as its hollow structure enhanced the charge carrier separation efficiency and the light absorption capacity of the hybrid catalyst. Furthermore, after the decoration of Au nanoparticles, the formed Schottky junction further discouraged the charge carrier recombination. Thus, the cooperative p-n heterojunction and Schottky junction greatly facilitated photocatalytic CO2 reduction, and exhibiting the maximum CO and CH4 yields of 140.1 and 77.5 μmol g−1 h−1, respectively. This work presents an efficient design of high-performance catalysts for photocatalytic CO2 reduction.

Activation of Bi2MoO6/Zn0.5Cd0.5S charge transfer through interface chemical bonds and surface defects for photothermal catalytic CO2 reduction

The photocatalytic reduction of CO2 to high-value fuels has been proposed as a solution to the energy crisis caused by the depletion of energy resources. Despite significant advancements in photocatalytic CO2 reduction catalyst development, there are still limitations such as poor CO2 adsorption/activation and low charge transfer efficiency. In this study, we employed a defect-induced heterojunction strategy to construct atomic-level interface Cd-O bonds and form Bi2MoO6/Zn0.5Cd0.5S heterojunctions. The sulfur vacancies (VS) formed in Bi2MoO6/Zn0.5Cd0.5S acted as activation sites for CO2 adsorption. While the interfacial stability provided by the Cd-O bonds served as an electron transfer channel that facilitated the movement of electrons from the interface to the catalytic site. The VS and Cd-O bonds simultaneously influence the distribution of charge, inducing the creation of an interface electric field that facilitates the upward displacement of the center of the d-band. This enhances the adsorption of reaction intermediates. The optimized Bi2MoO6/Zn0.5Cd0.5S heterostructure exhibited high selectivity and stability of photoelectrochemical properties for CO, generating 42.97 μmol⋅g−1⋅h−1 of CO, which was 16.65-fold higher than Zn0.5Cd0.5S under visible light drive. This research provides valuable insights for designing photocatalyst interfaces with improved CO2 adsorption conversion efficiency.

Interface Induced by Hydrothermal Aging Boosts the Low-Temperature Activity of Cu-SSZ-13 for Selective Catalytic Reduction of NOx.

Hitherto, sulfur poisoning and hydrothermal aging have still been the challenges faced in practical applications of the Cu-SSZ-13 catalyst for the selective catalytic reduction (SCR) of NOx from diesel engine exhaust. Here, we elaborately design and conduct an in-depth investigation of the synthetic effects of hydrothermal aging and SO2 poisoning on pristine Cu-SSZ-13 and Cu-SSZ-13@Ce0.75Zr0.25O2 core@shell structure catalysts (Cu@CZ). It has been discovered that Cu@CZ susceptible to 750 °C with 5 vol % H2O followed by 200 ppm SO2 with 5 vol % H2O (Cu@CZ-A-S) could still maintain nearly 100% NOx conversion across the significantly wider temperature region of 200-425 °C, which is remarkably broader than that of the Cu-SSZ-13-A-S (300-400 °C) counterpart. The experimental results show that the hydrothermal aging process results in the migration of highly active Cu species within the cage of Cu-SSZ-13 to the CZ surface, forming CuO/CZ with abundant interfaces, which significantly enhances the adsorption and subsequent activation of NO, leading to the generation of reactive N2O3 and HONO intermediates. Moreover, density functional theory (DFT) calculations reveal that the H of the HONO* species can function as Brønsted acid sites, effectively adsorbing NH3 to generate the active NH4NO2* intermediate, which readily decomposes into N2 and H2O. Furthermore, this pathway is the rate-determining step with an energy barrier of 0.93 eV, notably lower than that of the "standard SCR" pathway (1.42 eV). Therefore, the formation of the new CuO/CZ interface profoundly boosts the low-temperature NH3-SCR activity and improves the coresistance of the Cu@CZ catalyst to sulfur poisoning and hydrothermal aging.

Enhanced NH3-SCR performance using hydrothermally synthesized cell-like MnOx loaded rectorite catalysts

This study evaluates the catalytic performance of hydrothermally synthesized MnOx loaded rectorite catalysts (MnOx/REC-HP) in the selective catalytic reduction of NH3-SCR. Comparative analyses were conducted with catalysts synthesized via pore-volume impregnation, coprecipitation, and in-situ deposition methods, all yielding comparable manganese mass fractions. Results reveal that catalysts derived from hydrothermal synthesis outperform others in NH3-SCR activity across the 100–300 °C temperature spectrum. MnOx/REC-HP exhibits a distinctive cell-like structure of supported MnOx atop the rectorite substrate, diverging from the particulate patterns observed in other synthesis methods. Hydrothermal synthesis of metal precursors into their respective metal oxides effectively meets the fundamental requirements for SCR composites. This method enables the production of composites that are uniformly attached to nanostructures with high purity and controlled crystallinity. The rectorite surface is embellished with a meticulously arranged honeycomb structure of MnOx, augmenting the BET surface area, intensifying redox capability, enhancing NH3 and NOx adsorption, and amplifying the Mn4+ molar ratio on the catalyst surface. Consequently, MnOx/REC-HP showcases remarkable low-temperature NH3-SCR performance.

Self-powered wearable biosensor based on stencil-printed carbon nanotube electrodes for ethanol detection in sweat

Herein we introduce a novel water-based graphite ink modified with multiwalled carbon nanotubes, designed for the development of the first wearable self-powered biosensor enabling alcohol abuse detection through sweat analysis. The stencil-printed graphite (SPG) electrodes, printed onto a flexible substrate, were modified by casting multiwalled carbon nanotubes (MWCNTs), electrodepositing polymethylene blue (pMB) at the anode to serve as a catalyst for nicotinamide adenine dinucleotide (NADH) oxidation, and hemin at the cathode as a selective catalyst for H2O2 reduction. Notably, alcohol dehydrogenase (ADH) was additionally physisorbed onto the anodic electrode, and alcohol oxidase (AOx) onto the cathodic electrode. The self-powered biosensor was assembled using the ADH/pMB-MWCNTs/SPG||AOx/Hemin-MWCNTs/SPG configuration, enabling the detection of ethanol as an analytical target, both at the anodic and cathodic electrodes. Its performance was assessed by measuring polarization curves with gradually increasing ethanol concentrations ranging from 0 to 50 mM. The biosensor demonstrated a linear detection range from 0.01 to 0.3 mM, with a detection limit (LOD) of 3 ± 1 µM and a sensitivity of 64 ± 2 μW mM−1, with a correlation coefficient of 0.98 (RSD 8.1%, n = 10 electrode pairs). It exhibited robust operational stability (over 2800 s with continuous ethanol turnover) and excellent storage stability (approximately 93% of initial signal retained after 90 days). Finally, the biosensor array was integrated into a wristband and successfully evaluated for continuous alcohol abuse monitoring. This proposed system displays promising attributes for use as a flexible and wearable biosensor employing biocompatible water-based inks, offering potential applications in forensic contexts.Graphical A novel water-based graphite ink modified with multiwalled carbon nanotubes designed for the development of a wearable self-powered biosensor enabling alcohol abuse detection through sweat analysis.

Adsorption and decomposition of perfluorinated compounds using NiSBA-15 and CuSBA-15 catalysts for greenhouse gas reduction

BackgroundThe persistence of the environmental effects of perfluorinated compounds (PFCs) and fluorinated compounds (FCs) has raised concerns due to their widespread use and long-term impact on ecosystems and human health. MethodsIn this study, we investigated the use of NiSBA-15 and CuSBA-15 catalysts for the adsorption and decomposition of PFCs/FCs (CF₄, SF₆, NF₃, C₃F₈, and C₄F₈) by varying parameters such as weight percentage and contact time. The catalysts were synthesized through an impregnation method with stirring at 300 rpm for 24 h, followed by calcination at 550 °C for 6 h. The catalytic decomposition of NF₃ was conducted using a glass reactor with precise flow rate control and FT-IR monitoring. Variations in acid concentration during synthesis led to structural changes, transitioning from elongated rods to doughnut-like shapes and eventually spherical structures. Impregnation with nickel and copper nitrates successfully modified SBA-15, forming NiSBA-15 and CuSBA-15, as confirmed by HR-TEM images displaying black spots. Catalytic PFC decomposition experiments using unmodified SBA-15 showed limited efficiency, achieving only 15 % NF₃ removal at 500 ppm and 500 °C over 1000 min. Subsequent modification with nickel and copper significantly improved NF₃ removal efficiency. Significant ResultsCuSBA-15 exhibited superior performance compared to NiSBA-15, reaching a remarkable 95 % removal efficiency of NF3. Kinetic analysis using a pseudo-first-order reaction model demonstrated the enhanced catalytic efficiency of the modified SBA-15 catalysts, with increased reaction rate constants (K) for NF3 decomposition. This study reveals the potential of NiSBA-15 and CuSBA-15 catalysts for the adsorption and decomposition of specific PFCs/FCs, offering valuable insights into the underlying mechanisms and practical applications of these catalysts.

Compositional and Fabrication Cycle Optimization of Ceria-Zirconia-Supported Mo-Based Catalysts for NH3-SCR NOx Reduction

The reduction of nitrogen oxides (NOx), critical pollutants from stationary to mobile sources, mainly relies on the selective catalytic reduction (NH3-SCR) method, employing ammonia to reduce NOx into nitrogen and water. However, conventional catalysts, while effective, pose both environmental and operational challenges. This study investigates ceria-zirconia-supported molybdenum-based catalysts, exploring the effects of zirconium doping and different catalyst synthesis techniques, i.e., co-precipitation and impregnation. The catalytic performance of the differently prepared samples was significantly influenced by the molybdenum incorporation method and the zirconium content within the ceria-zirconia support. Co-precipitation at higher temperatures resulted in catalysts with better structural attributes but slightly lower catalytic activity compared to those prepared via impregnation. Optimal NOx reduction (close to 100%) was observed at a 15 mol% zirconium doping level when using the impregnation method.

Novel Nanocatalysts for Simultaneous Ammonia Oxidation and Nitrate Reduction

Throughout recent years, nitrate reduction to ammonia has gained popularity in the scientific world to produce a carbon-free fuel [1]. However, research has primarily focused on low-concentration nitrate reduction, specifically for wastewater remediation. High-concentration effluents, such as ANSOL (Ammonium Nitrate), have emerged as a significant waste byproduct and a threat [2], with explosive characteristics and increasing production rates over the years [3]. This research seeks solutions to incorporate onsite waste treatment for generating electrical power, emphasizing the integration of waste streams as a distinctive opportunity. The integration aims to facilitate both power generation and the provision of clean water, with a focus on developing prototype systems designed to convert challenging Department of Defense (DoD) waste streams containing ANSOL into usable fuels for onsite energy generation.In this presentation, results from two distinct systems employing nanoparticle catalysts for the reduction of nitrates to ammonia, while simultaneously oxidizing ammonia to nitrogen and hydrogen, are discussed. This is particularly relevant in the presence of a high concentration of ammonium nitrate in waste (>0.5 M) with industrially relevant electrochemical performance (>300 mA/cm2 with Faradaic Efficiencies higher than 50%). The initial approach involves the integration of CuNi/C and Pt3Ir/C catalysts for reduction and oxidation, respectively [4]. The subsequent approach underscores pulsed electrodeposition of CuNi [5] for nanoparticle synthesis in the reduction process, coupled with the use of Pt3Ir/C catalyst for oxidation. The effect of different applied potentials was studied for the conversion of NO3 - to NH3 and subsequent H2 production. Electrode stability and process integration were investigated.[1] Kani, N. C., Nguyen, N. H. L., Markel, K., Bhawnani, R. R., Shindel, B., Sharma, K., Kim, S., Dravid, V. P., Berry, V., Gauthier, J. A., Singh, M. R., “Electrochemical Reduction of Nitrates on CoO Nanoclusters-Functionalized Graphene with Highest Mass Activity and Nearly 100% Selectivity to Ammonia,” Adv. Energy Mater. 2023, 13, 2204236.[2] United States Occupational Safety and Health Administration, Bureau of Alcohol, Tobacco, Firearms and Explosives, Environmental Protection Agency, "Chemical Advisory: Safe Storage, Handling, and Management of Solid Ammonium Nitrate Prills," EPA 550-F-15-001, June 2015.[3] Strategic Environmental Research and Development Program (SERDP) and Environmental Security Technology Certification Program (ESTCP), "Conversion of Ammonium Nitrate Solutions to Useful Products," SERDP and ESTCP Website, April 5, 2021. [Online].[4] Hariri, M.B., and Botte, G.G., "Simultaneous Removal of Ammonia and Nitrate from Wastewater Using a Pulse Electrolysis Technique," Journal of The Electrochemical Society 170.5. 2023.[5] I. Baskaran, T.S.N. Sankara Narayanan, and A. Stephen, "Pulsed electrodeposition of nanocrystalline Cu–Ni alloy films and evaluation of their characteristic properties," Materials Letters, vol. 60, no. 16, pp. 1990-1995, July 2006.

(Invited) Single-Atom Cu Catalysts for Electrochemical CO2 Reduction – Combining Theory, Synthesis and Electrochemical Characterization

Electrochemical CO2 reduction (CO2RR) is a leading sustainable approach for transforming atmospheric CO2 into valuable chemicals. This electrocatalytic process relies on a delicate balance of electron and proton transfer steps, resulting in the formation of diverse 1-carbon and some 2-carbon products, contingent on the surface properties. Extensive exploration of various transition metals for CO2RR has revealed that the binding strength of reaction intermediates on these metals significantly influences product selectivity. Notably, metals such as Au, Ag, Pd, Zn, Cd, Bi, Sn, and In, recognized for their activity in CO2RR, exhibit lower binding strengths for CO2 intermediates, leading to the predominant production of either HCOOH or CO as sole products. In contrast, Cu, with its moderate ability to bind CO2RR intermediates, yields multiple products during CO2RR, albeit with reduced selectivity [1]. Moreover, the overall efficiency of CO2 conversion is hampered by the simultaneous occurrence of the competing hydrogen evolution reaction (HER) at the potentials required for producing desired products. Thus, it is imperative to develop new, effective catalysts. Catalysts capable of suppressing HER while enhancing selectivity are essential for advancing the overall efficiency of CO2 conversion [2].Single-atom catalysts (SACs) are a relatively new class of materials that hold great promise due to their high specific activity and maximum atom utilization [3]. These catalysts often provide singular types of active sites, enhancing selectivity in reactions. However, the vast array of possible SACs, deployable on various supports, makes it impractical, if not possible, to use the traditional trial-and-error studies to yield high performing catalysts within reasonable timeframes. To navigate this complexity, theoretical investigations, especially DFT computations and machine learning techniques, have emerged as powerful tools. They can facilitate the identification of suitable catalyst structures and enable the precise engineering of atomic arrangement, therefore achieving targeted product formation from CO2 with enhanced conversion efficiency. Additionally, conventional synthesis methods suffer from various drawbacks, involving multiple steps, harsh conditions, and a lack of control over the metal site distribution in the carbon matrix, limiting the desired coordination structure [4, 5].Therefore, the work presented in this talk represents our combined experimental-theoretical effort. Specifically, Cu single atoms were strategically deposited onto defective carbon supports and systematically investigated for their performance as CO2RR electrocatalysts. These catalysts were inspired by DFT results showing how the product profile could be manipulated on catalyst surfaces, along with a prediction of the most likely products that would arise from the reaction.These catalysts were synthesized using a novel method denoted as switched solvent synthesis. This approach involves initially impregnating metals onto a carbon support, followed by switching the solvent from aqueous to an organic solvent with a higher dipole moment, and subsequently reducing the resulting mixture under an H2 environment. This innovative method offers notable advantages, enabling the efficient production of SACs in less time, at lower temperatures (~100-500 °C), and with high yields. In this study, Cu SACs were synthesized, and the influence of reaction parameters on the distribution of Cu metal atoms was systematically examined. The confirmation of SAC formation was achieved through various characterization techniques, including aberration-corrected STEM, XRD, and XPS.To assess the electrochemical activity and CO2 reduction abilities of the Cu SACs, electrochemical characterization techniques were employed under both He and CO2-saturated 0.1 M KHCO3 electrolytes. Furthermore, the product distribution and CO2 conversion efficiencies, including activity, stability, selectivity, and faradaic efficiency, of the Cu SACs were rigorously evaluated through electrolysis in a flow cell setup. Quantification of the results was performed using an integrated GC/MS instrument.

(Invited) Photocatalyst Sheets for Scalable Solar Fuels Production from Water and CO2

The development of sunlight-driven water splitting or CO2 reduction systems with high efficiency, scalability, and cost-competitiveness is a central issue for mass production of fuels and energy-rich chemicals.1 Z-scheme photocatalytic systems, employing the two-step photoexcitation of photocatalyst I (PC I) and photocatalyst II (PC II), have garnered significant attention. These systems can utilize narrow bandgap semiconductors capable of either water/CO2 reduction or oxidation potential, enabling the conversion of solar energy. The challenge in developing a Z-scheme system lies in ensuring efficient electron transfer between PC I and PC II.2 To address these challenges, we have developed all-solid-state devices—photocatalyst sheets—for photocatalytic water splitting.3,4 These sheets establish a direct connection between PC I and PC II particles via a conductive layer or conductive nanoparticles, effectively facilitating electron transfer between them. Consequently, these photocatalyst sheets achieve a high solar-to-H2 conversion efficiency exceeding 1%. They outperform analogous powder suspension and photoelectrochemical systems in their optimal reaction solutions due to the effective electron transfer enabled by the conductive layer or nanoparticles bridging PC I and PC II. Compared to traditional photoelectrochemical systems, the photocatalyst sheet design significantly reduces the effects of H+/OH− concentration overpotentials and the IR drop due to the proximity of PC I and PC II in the sheet. Hence, the design of these photocatalyst sheets proves highly suitable for efficient large-scale applications.Additionally, efforts to demonstrate fuel production from CO2 powered by sunlight are currently hampered by the requirements of sacrificial electron donors or external bias, and lack of efficiency, selectivity and scalability. To overcome those barriers, we integrate a selective molecular catalyst on semiconductor light absorbers to form a wireless and monolithic photocatalyst sheet.5 For instance, by incorporating a phosphonated cobalt(II) bis(terpyridine) catalyst (CotpyP) onto a modified SrTiO3:La,Rh|Au|BiVO4:Mo sheet, we have achieved a solar-to-formate conversion efficiency of 0.08%. This configuration harnesses the high selectivity of molecular catalysts for CO2 reduction and the strong water oxidation power of semiconductors, yielding a formate selectivity of 97±3% through the coupled process of CO2 reduction and water oxidation. We have also developed a bio-abiotic hybrid system by combining a photocatalyst sheet, capable of scalable photocatalytic water splitting, with nonphotosynthetic bacteria acting as biocatalysts.6 When pairing CO2-fixing acetogenic bacteria, Sporomusa ovata, with a SrTiO3:La,Rh|ITO|BiVO4:Mo sheet, a solar-to-acetate conversion efficiency of ~0.7% was achieved (as shown in the figure). This coupling exhibited an impressive selectivity for acetate production in CO2 reduction reactions, reaching ~100%.Our study offers novel and versatile strategies toward sustainable solar fuel production.References Q. Wang, C. Pornrungroj, S. Linley, E. Reisner. Nat. Energy 7 , 13–24 (2022)Y. Sasaki, H. Nemoto, K. Saito, A. Kudo. J. Phys. Chem. C 113, 17536–17542 (2009)Q. Wang, T. Hisatomi, Q. Jia, H. Tokudome, M. Zhong, C. Wang, Z. Pan, T. Takata, M. Nakabayashi, N. Shibata, Y. Li, I. D. Sharp, A. Kudo, T. Yamada, K. Domen. Nat. Mater. 15,611–615 (2016)Q. Wang, T. Hisatomi, Y. Suzuki, Z. Pan, J. Seo, M. Katayama, T. Minegishi, H. Nishiyama, T. Takata, K. Seki, A. Kudo, T. Yamada, K. Domen. J. Am. Chem. Soc. 139, 1675–1683 (2017)Q. Wang, J. Warnan, S. Rodríguez-Jiménez, J. J. Leung, S. Kalathil, V. Andrei, K. Domen, E, Reisner. Nat. Energy 5, 703–710 (2020)Q. Wang, S. Kalathil, C. Pornrungroj, D. C. Sahm, E. Reisner. Nat. Catal. 5, 633–641 (2022) Figure 1