Aqueous Catalyst Research Articles

Synergistic effect of diatomaceous earth as a catalyst and terephthalic acid as a co-catalyst on chemical recycling of polyethylene terephthalate via hydrolysis

Polyethylene terephthalate (PET) is one of the most useful commodity polymers that have been used extensively in packaging and textile industry and hence it has become a concerning waste. In this work, diatomaceous earth (DE), terephthalic acid (TPA) and distilled water were used to hydrolyze PET waste from drinking water bottles into TPA and ethylene glycol (EG). TPA can be used as one of the monomers for the synthesis of PET or other industrial applications such as for the synthesis of alkyd resins. Here DE was used as a solid catalyst which can be separated by a simple filtration after the TPA removal, in contrast to the majority of earlier efforts, which used aqueous acid or base catalysts that are difficult to separate. Additionally, commercial TPA, which is used as co-catalyst, can easily be substituted by produced TPA from the PET hydrolysis. The conversion of PET and the yield of TPA, using 5.0 wt % of DE and 3.0 wt % of commercial TPA with a PET:H2O mass ratio of 1.0:3.0, at 185 °C and 11.2 bar was 100 % and 95.40 % respectively, obtained in 2.5 h. TPA product was isolated from the reaction mixture by basic wash and subsequent neutralization and it was characterized by infrared spectroscopy, nuclear magnetic resonance, differential scanning calorimetry, X-ray diffraction and thermogravimetric analysis. The effects of reaction parameters such as reaction temperature, reaction time, mass ratio of PET:H2O and the catalysts loading on the yield of TPA were studied. The optimized reaction was repeated over seven consecutive reaction cycles using recovered DE to further demonstrate the effectiveness of reused DE and it was found that the outcomes were unaltered. Due to DE's affordability and accessibility, this reaction is a green and convenient way to handle the staggering accumulation of PET waste.

Integrated techno-economic and life cycle assessment of hydroformylation in microemulsion systems

This paper presents the first integrated techno-economic and life cycle assessment of microemulsion systems being applied for rhodium-catalyzed hydroformylation of long-chain alkenes at industrial scale. The case study describes a projected 150 kt/a production of tridecanal (US gulf coast, 2019). The industrial success of the hydroformylation of short-chain alkenes lies in the continuous recycling of the rhodium-containing water phase. Microemulsion systems can be applied to transfer this concept to long-chain alkenes by overcoming the miscibility gap between the aqueous catalyst phase and the unipolar alkene phase and, moreover, by generating a temperature-induced multi-phase system enabling the immobilization of the catalyst and its continuous recycling, as demonstrated in miniplant operations with dodecene and rhodium/SulfoXantPhos. Customizable simulation models have been developed for scale-up and assessment of the miniplant data. Surprisingly, a profitability-driven sensitivity study indicates a base case optimum at low residence time with low alkene conversion leading to large throughput streams and high raw material purge rates. The comparison to the industrial cobalt-based benchmark system shows an economic advantage regarding net present value (Rh: 68 M$; Co: 62 M$), while about half of the environmental indicators are in favor or equivalent. In a best-case scenario considering zero leaching of expensive rhodium the net present value increases by almost 40% accompanied by a shift to overall lower environmental impacts than the benchmark. In conclusion, the investigated miniplant data suggest microemulsion systems to be competitive when applied in continuous processes at a large scale.

Thermochemical Conversion of Animal-Derived Waste: A Mini-Review with a Focus on Chicken Bone Waste

Food waste, particularly animal-derived waste, presents a significant challenge globally, prompting the need for sustainable management strategies. In 2022, the amount of food waste per capita reached 131 kg/capita in the EU (European Union), which is why the search for environmentally friendly ways to manage food waste through thermochemical conversion processes has gained momentum in recent years. Animal-derived waste is a good source of organic matter (proteins, lipids, and polysaccharides) and mineral compounds (calcium phosphate, mostly hydroxyapatite). This composition makes animal-derived waste valuable for the extraction of chemical compounds, such as hydroxyapatite (HAp), which constitutes up to 70 wt% of animal bones; keratin; collagen; and hyaluronic acid (HA), to produce pharmaceutical, medical, or industrial by-products. The thermochemical conversion of chicken bones through pyrolysis and gasification creates a new opportunity to valorize this type of waste by reintroducing valuable by-products into the economy and thus achieving sustainable waste management objectives. The results of this study showcase the multiple applications of the pyrolysis of chicken bone waste products (as adsorbents in aqueous mediums, catalysts, fertilizers, and biomedical applications) and the necessity of a better exploration of the gasification process of chicken bone waste. Therefore, this study explores the properties of animal-derived waste and discusses the pyrolysis and gasification of chicken bone waste, the influence of process conditions on product yields, and the catalytic enhancement of these thermochemical processes.

Biopolymer-supramolecular polymer hybrids for photocatalytic hydrogen production.

Solar generation of H2 is a promising strategy for dense energy storage. Supramolecular polymers composed of chromophore amphiphile monomers containing perylene monoimide (PMI) have been reported as crystalline light-harvesting assemblies for aqueous H2-evolving catalysts. Gelation of these supramolecular polymers with multivalent ions creates hydrogels with high diffusivity but insufficient mechanical stability and catalyst retention for reusability. We report here on using sodium alginate (SA) biopolymer to both induce supramolecular polymerization of PMI and co-immobilize them with catalysts in a robust hydrogel with high diffusivity that can also be 3D-printed. Faster mass transfer was achieved by controlling the material macrostructure by reducing gel diameter and microstructure by reducing biopolymer loading. Optimized gels produce H2 at rates rivaling solution-based PMI and generate H2 for up to 6 days. The PMI assemblies in the SA matrix create a percolation network capable of bulk-electron transfer under illumination. These PMI-SA materials were then 3D-printed on conductive substrates to create 3D hydrogel photoelectrodes with optimized porosity. The design of these versatile hybrid materials was bioinspired by the soft matter environment of natural photosynthetic systems and opens the opportunity to carry out light-to-fuel conversion within soft matter with arbitrary shapes and particular local environments.

O2-Independent H2O2 Production via Water-Polymer Contact Electrification.

Hydrogen peroxide (H2O2), as a critical green chemical, has received immense attention in energy and environmental fields. The ability to produce H2O2 in earth-abundant water without relying on low solubility oxygen would be a sustainable and potentially economic process, applicable even to anaerobic microenvironments, such as groundwater treatment. However, the direct water to H2O2 process is currently hindered by low selectivity and low production rates. Herein, we report that poly(tetrafluoroethylene) (PTFE), a commonly used inert polymer, can act as an efficient triboelectric catalyst for H2O2 generation. For example, a high H2O2 production rate of 24.8 mmol gcat-1 h-1 at a dosage of 0.01 g/L PTFE was achieved under the condition of pure water, ambient atmosphere, and no sacrificial agents, which exceeds the performance of state-of-the-art aqueous H2O2 powder catalysts. Electron spin resonance and isotope experiments provide strong evidence that water-PTFE tribocatalysis can directly oxidize water to produce H2O2 under both anaerobic and aerobic conditions, albeit with different synthetic pathways. This study demonstrates a potential strategy for green and effective tribocatalytic H2O2 production that may be particularly useful toward environmental applications.

Comparing Ultralong Carbon Nanotube Growth from Methane over Mono- and Bi-Metallic Iron Chloride Catalysts.

This research endeavours to study the growth of ultralong carbon nanotubes (UL-CNTs) from methane using diverse catalysts, namely FeCl3, bi-metallic Fe-Cu, Fe-Ni, and Fe-Co chlorides. Aqueous catalyst solutions were evenly dispersed on silica substrates and grown at 950 °C in the presence of hydrogen via a horizontal chemical vapour deposition (CVD) furnace. The samples underwent characterisation by Raman spectroscopy, scanning electron microscopy (SEM), and optical microscopy to identify the quality of CNTs and enumerate individual UL-CNTs. Our findings revealed that FeCl3, as a mono-metallic catalyst, generated the longest UL-CNTs, which measured 1.32 cm, followed by Fe-Cu (0.85 cm), Fe-Co (0.7 cm), and Fe-Ni (0.6 cm), respectively. The G/D ratio (graphene to defects) from the Raman spectroscopy was the highest with the FeCl3 catalyst (3.09), followed by Fe-Cu (2.79), Fe-Co catalyst (2.13), and Fe-Ni (2.52). It indicates that the mono-iron-based catalyst also produces the highest purity CNTs. Moreover, this study scrutinises the vapour-liquid-solid (VLS) model for CNT growth and the impact of carbide formation as a precursor to CNT growth. Our research findings indicate that forming iron carbide (Fe3C) is a crucial transition phase for amorphous carbon transformation to CNTs. Notably, the iron catalyst generated the longest and densest CNTs relative to other iron-based bi-metallic catalysts, which is consistent with the temperature of carbide formation in the mono-metallic system. From correlations made using the phase diagram with carbon, we conclude that CNT growth is favoured because of increased carbon solubility within the mono-metallic catalyst compared to the bi-metallic catalysts.

Aqueous air cathodes and catalysts for metal–air batteries

Metal–air batteries hold the promise of high specific energy and benign, recyclable components, which are critical to the long term goal of eliminating the use of fossil fuels. The critical components of metal–air batteries include the cathode electrocatalysts and the compatible electrolyte, which together enable the oxygen evolution (OER) and oxygen reduction (ORR) reactions, determining much of the battery's performance. In this review, we summarize the current status of research on bifunctional oxygen electrocatalysts for aqueous electrolytes and look forward to the advances which need to be made to achieve the promise of metal–air batteries.

Extractive Catalytic Oxidative Deoxygenation of Model Fuels Catalyzed by a Vanadium-Substituted Heteropolyacid and Molecular Oxygen

Extractive catalytic oxidative deoxygenation (ECODO) completes extractive catalytic oxidative desulfurization (ECODS) and extractive catalytic oxidative denitrogenation by removing organic oxygen from fuels. This is particularly necessary for renewable fuels to make them more stable and efficient. In ECODO, compounds such as cresol, furan, and their derivatives could be completely oxidized under oxygen at 20 bar and 120 °C using an aqueous heteropolyacid catalyst solution. The oxidation products were separated in situ in the three-phase process, either as CO2 or CO in the gas phase or as water-soluble organic acids like formic and acetic acid as well as acetone. In the case of stable dibenzofuran (DBF), the conversion could be drastically increased from only 27% to above 50% by tuning the reaction conditions and optimizing the catalyst loading by a design of experiment. Moreover, the amount of oxygen in the gas phase could be drastically reduced from 20 to 4 bar operating in 20 bar of synthetic air without limiting the performance of the catalyst. Furthermore, it could be shown that the parallel ECODS in the presence of an oxygenate like DBF leads to better desulfurization of model gasoline than without. The ECODO therefore offers a potential alternative to the classical hydrodeoxygenation, which is not only more energy-efficient but also replaces the expensive hydrogen with cheap air and avoids additional unit operations for fuel cleaning.

Design and techno–economic analysis of levulinic acid production process from biomass by using co-product formic acid as a catalyst with minimal waste generation

Levulinic acid (LA) is an essential biomass-derived platform chemical that can be converted into value–added chemicals such as polymers, fertilisers, and pharmaceuticals. However, the high energy demand and cost required in the separation process are significant issues in the LA production process. Recently, formic acid (FA), the co–product in biomass–LA reaction, has been focused on as a catalyst for both biomass pretreatment and LA production. This study designed and numerically simulated a novel process for producing LA from wheat straw (feed rate: 100 kg/h) using an FA aqueous catalyst system (60, 70, and 80 wt%). The reaction data were referred to previous kinetics studies in order to evaluate the feasible reaction time from an economic perspective. The minimised waste generation process was designed by recovering the FA catalyst and using solid residues (lignin and humins) as heat sources. Another byproduct, furfural, was utilised as an extractant for purifying the LA and recovering unreacted products. The minimum selling price (MSP) of the LA and furfural was calculated with an internal rate of return of 6.1% for 20 years. The MSPs were calculated to be 9.59–12.8 USD/kg–products, which was higher than the market price and previous studies. However, the net required energy in this process was − 5.37 to − 32.1 MJ/kg–LA, indicating that the combustion of the solid residue can supply all of the energy required for the process. Our novel concept based on the byproduct utilisation for heat source and extractant can be an effective strategy for an implication of the biorefinery process that can circulate energy with minimum waste generation.

Ethanol organosolv pretreatment of sugarcane bagasse assisted by organic acids and supercritical carbon dioxide

The scCO2-assisted organosolv pretreatment of sugarcane bagasse was carried out using aqueous ethanol and organic acid catalysts. Variables involved were temperature (150–190 °C), time (0–60 min), type of catalyst (acetic, citric, and oxalic acids), amount of CO2 (25–50 g), ethanol titer in water (0–80 vol%), and catalyst concentration (0.5 to 1.5 % w·v−1). The best delignification (86 wt%) and glucan retention (89 wt%) were achieved at 170 °C for 15 min using 60 vol% ethanol in water, 1 wt% oxalic acid, and 25 g CO2. Organic acid esterification was a limitation for pretreatment operations using ethanol titers above 60 vol%. Enzymatic hydrolysis of pretreated materials at 1 % (w·v−1) glucans released 74.3 ± 0.2 % glucose in 96 h using Cellic CTec3 (Novozymes) at 9.89 FPU·gglucans−1. The concentrated pretreatment liquor allowed lignin recovery by water precipitation in high yields, while the aqueous supernatant contained low levels of fermentation inhibitors.

Improvement of electrochemically mediated atom transfer radical polymerization: Use of aluminum as a sacrificial anode in water

The simplest electrolytic devices are undivided electrochemical cells without any separator between anodic and cathodic compartments. These simple yet efficient electrochemical cells often require the use of sacrificial metal counter electrodes, which, however, are incompatible with many electrocatalytic systems. In this article, we investigate the effect of the presence of an Al anode on an electrocatalytic reaction in water, namely electrochemically-mediated atom transfer radical polymerization (eATRP) catalyzed by common Cu complexes with amine ligands. It was found that the sacrificial anode could undermine the reactivity of the aqueous Cu catalysts in two ways: i) protonation of the amine ligand promoted by the release of acidic Al3+ ions; ii) spontaneous deposition of Cu0 on the Al metal surface. Both pathways led to decomposition of the original copper catalyst. To avoid undesired side reactions arising from the Al anode, simple strategies involving the use of appropriate amine ligands and pH buffers are described.

Copper‐Catalysed Synthesis of Propargyl Alcohol and Derivatives from Acetylene and other Terminal Alkynes

AbstractA copper(I)/phosphine system that homogeneously catalyses the alkynylation of formaldehyde with acetylene or terminal alkynes is reported. Using acetylene at atmospheric pressure, the catalyst consisting of <1 mol% copper(I) phenylacetylide and a trialkyl bisphosphine ligand shows a high selectivity towards the formation of propargyl alcohol rather than 1,4‐butynediol, which is not reported for common heterogeneous copper acetylide catalysts. The biphasic water/toluene reaction mixture allows the separation of targeted products with the aqueous layer and catalyst recycling via the organic layer.magnified image

Enzyme Encapsulation by Facile Self-Assembly Silica-Modified Magnetic Nanoparticles for Glucose Monitoring in Urine.

Silica nanoparticles hold tremendous potential for the encapsulation of enzymes. However, aqueous alcohol solutions and catalysts are prerequisites for the production of silica nanoparticles, which are too harsh for maintaining the enzyme activity. Herein, a procedure without any organic solvents and catalysts (acidic or alkaline) is developed for the synthesis of silica-encapsulated glucose-oxidase-coated magnetic nanoparticles by a facile self-assembly route, avoiding damage of the enzyme structure in the reaction system. The encapsulated enzyme was characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive spectrometry, and a vibrating sample magnetometer. Finally, a colorimetric sensing method was developed for the detection of glucose in urine samples based on the encapsulated glucose oxidase and a hydrogen peroxide test strip. The method exhibited a good linear performance in the concentration range of 20~160 μg mL−1 and good recoveries ranging from 94.3 to 118.0%. This work proves that the self-assembly method could be employed to encapsulate glucose oxidase into silica-coated magnetic particles. The developed colorimetric sensing method shows high sensitivity, which will provide a promising tool for the detection of glucose and the monitoring of diabetes.

Negatively charged nanofiltration membrane with high performance via the synergetic effect of benzidinedisulfonic acid and trimethylamine during interfacial polymerization

Negatively charged surface is preferred for thin film composite (TFC) nanofiltration (NF) membrane with excellent separation performance for divalent anions, and ultra-smooth surface is beneficial for antifouling in practical application. Herein a kind of high-flux sulfonated polyamide TFC NF membrane, termed as TFC-BDSA, was successfully fabricated via interfacial polymerization (IP) between the aqueous monomers, 2,2-benzidinedisulfonic acid (BDSA) mixed with piperazine (PIP), and the organic monomer, trimesoyl chloride (TMC), with triethylamine (TEA) as aqueous catalyst. The results proved that BDSA and TEA have synergetic effect on the performance of the fabricated NF membrane. BDSA enabled the formation of more negatively charged, more hydrophilic and much smoother surfaces, which greatly improved the separation performance and antifouling capability of the prepared TFC-BDSA membrane. TEA not only act as an acid receiver, but could form a complex salt with BDSA and thus help to manipulate the diffusion rate of BDSA and PIP as well as the interfacial polymerization process, which helps to form a more smooth, more hydrophilic, more negatively charged, as well as more antifouling and defect-free membrane skin layer. With 1.0 wt% BDSA in the aqueous monomer solution and at pH 11.2 which is adjusted by TEA, the resultant TFC-BDSA membrane displays an excellent water permeance of 122 L m−2h−1 MPa−1, which is more than twice the pristine baseline TFC membrane. Meanwhile, the resultant TFC-BDSA membrane achieved an extremely higher Na2SO4 rejection of 99.6 %, which is more than 2.0 % higher than that of the latter. Moreover, the flux recovery ratios were 101.1 % and 99.5 % (after two cycles of filtration - cleaning) for the TFC-BDSA membrane fouled with sodium alginate and humic acid, respectively, indicating its excellent antifouling performance. Furthermore, the TFC-BDSA membrane shows an excellent operation stability over a 120 h filtration process. In summary, this study provides a new approach to prepare high performance NF membranes for water treatment.

An Agro‐Waste Based Eco‐Friendly Synthesis, Electrochemical Behavior and Anti‐oxidant Properties Evaluation of Pyrano[2,3‐c]pyrazole and Pyrazolyl‐4H‐chromenes Derivatives

AbstractAn efficient and economical one‐pot synthesis of pyrano[2,3‐c] pyrazoles and pyrazolyl‐4H‐chromenes using Water Extract of Mango Peel Ash (WEMPA) as a natural aqueous medium catalysts under microwave irradiation described. The microwave irradiation enhances the rate of the reaction, and decreases by‐product formation. The catalyst is obtained from the agro‐waste feedstock, by simple thermal treatment of dry peel of mango fruit followed by extraction of the resulted ash in water gave catalytic green solvent medium. In continuation of our research work on developing green chemistry protocol for bioactive molecule synthesis, herein, first time described pyrano[2,3‐c]pyrazole and pyrazolyl‐4H‐chromene derivative synthesis by the reaction of hydrazine hydrate (1), malononitrile (2), ethyl acetoacetate (3), aryl aldehydes (4), and/or salicylaldehyde (5). Some of the selected pyrano[2,3‐c]pyrazole (6) and pyrazolyl‐4H‐chromene (7) derivatives are tested for their in vitro antioxidant activity (free radical scavenging) by DPPH assay method. The assay result revealed, compounds 6 a, 6 h, 6 i and 7 d showed significant antioxidant activities comparison with refrence ascorbic acid. Some of the selected derivatives are characterized by FT‐IR, 1H‐, 13C‐NMR and mass spectrometry analysis, and also tested for their electrochemical behavior studies using a cyclic voltammetry.

Metal‐Free Derivatization of Benzhydrols with Organosilanes

AbstractA methodology for the direct coupling between benzhydryl alcohols and organotrimethylsilanes has been developed. This transformation occurs in the presence of a substoichiometric amount of an inexpensive, commercially available aqueous tetrafluoroboric acid catalyst. The developed conditions demonstrate good functional group tolerance to both electron‐donating and electron‐withdrawing substituents. Additionally, the reaction conditions do not require the exclusion of air and moisture.

Bipolar electrodeposition of gradient polypyrrole films as a catalyst matrix for anodic ethanol oxidation

Lateral gradient coatings displaying various compositions and microstructures along a single surface are desirable for material screening. Here we report a successful application of bipolar electrochemistry to deposit lateral gradient polypyrrole films on a graphite strip substrate. The gradient film shows varying morphologies and a wettability gradient along the length of the bipolar electrode, with superabsorbent property in the middle portion of the film. The film was use as a catalyst matrix for ethanol oxidation in alkaline electrolyte. Aqueous Ni(NO3)2 solution as the catalyst precursor was absorbed into the film. Area-step cyclic voltammetry was used to evaluate the electrocatalytic activity of various local parts along the gradient film to ethanol oxidation. The local surface with the highest catalytic activity was screened out and the excellent catalytic activity is attributed to the outstanding properties of this zone in both water absorption and electrical conductivity. The nickel oxide catalyst can be highly dispersed in the nanoporous network polymer matrix, due to the uniform penetration of the aqueous precursor solution into the superabsorbent film. XPS and EIS analyses support the catalytic mechanism based on the redox transition between NiOOH and Ni(OH)2. This work indicates that loading aqueous catalyst precursors into superabsorbent conducting polymer films may be a promising method for the preparation of electrocatalysts.

High separation performance thin film composite and thin film nanocomposite hollow fiber membranes via interfacial polymerization for organic solvent nanofiltration

Hollow fiber (HF) organic solvent nanofiltration (OSN) membrane has unique self-supporting structure and larger specific surface area over flat OSN membranes, which is much more beneficial for separation processes intensification in chemical related industries. The key of this technology is HF OSN membrane. However, the research works on HF OSN membranes was relatively less till now. In this work, an outer-skinned polyimide HF substrate membrane was spun, and then thin film composite (TFC) membrane was prepared via interfacial polymerization (IP) between ultra-low concentration m-phenylenediamine (MPD) in the aqueous phase and trimesoyl chloride (TMC) in the organic phase on the HF substrate surface, with sodium dodecyl sulfate (SDS) as aqueous additives and triethylamine (TEA) as aqueous catalyst, and subsequently accompanied by crosslinking and solvent activation procedures. Further, thin film nanocomposite (TFN) HF OSN membrane incorporated with graphene oxide (GO) was also prepared. The combination of lower MPD concentration with SDS and TEA as additives in the aqueous monomer solution promote the formation of a TFC HF OSN membrane with average roughness of less than 3 nm, and a rhodamine B (RDB) rejection close to 100%, together with an ethanol permeance higher than 12 L m−2 h−1 MPa−1 under the optimum fabrication conditions. The optimal TFN membrane at a doping GO content of 5.0 mg L−1 achieves up to 20 L m−2 h−1 MPa−1 for the ethanol permeance without sacrificing the RDB rejection (nearly 100%). Moreover, both HF OSN membranes possess good swelling resistance, which proves their application potential in organic solvent system.

Effects of aqueous phase circulation and catalysts on hydrothermal liquefaction (HTL) of penicillin residue (PR): Characteristics of the aqueous phase, solid residue and bio oil

Hydrothermal liquefaction (HTL) is a promising thermochemical technology for the treatment of hazardous wastes such as penicillin residue (PR). For the treatment of aqueous waste produced by PR in the HTL process, aqueous phase circulation is an attractive solution, both environmentally and economically. The present study shows that aqueous phase circulation can promote the transfer of organic matter from the aqueous phase to bio–oil. The content of organic acids and alcohols in the aqueous phase decreased significantly, and the bio–oil yield and energy recovery efficiency also increased. Under non–catalytic conditions, the bio–oil yield increased from 26.09 wt% to 33.72 wt%. The use of Na2CO3 as a catalyst further improved the bio–oil yield. After a single aqueous phase circulation, the bio–oil yield increased to 34.63 wt%, and the energy recovery efficiency increased to 66.94%. Under catalytic hydrothermal conditions, the content of organic acids in the bio–oil was reduced using aqueous phase circulations, which improved the quality of the bio–oil. At the same time, the Na2CO3 catalyst promoted the hydrolysis of PR to form small molecule organic matter, inhibited the formation of coke, and reduced the content of carbon, hydrogen and oxygen in the solid residue. An increase of cycle times led to excessive accumulation of Na2CO3, which had a negative impact on the yield of bio–oil. Nitrogen–containing compounds in the bio–oil increased to a certain extent, which renders it necessary to consider denitrification treatments in the future. The work provides a useful reference for further research on the preparation of high quality bio–oil by PR hydrothermal liquefaction.

Efficient electrocatalytic nitrogen reduction to ammonia with aqueous silver nanodots

The electrocatalytic nitrogen (N2) reduction reaction (NRR) relies on the development of highly efficient electrocatalysts and electrocatalysis systems. Herein, we report a non-loading electrocatalysis system, where the electrocatalysts are dispersed in aqueous solution rather than loading them on electrode substrates. The system consists of aqueous Ag nanodots (AgNDs) as the catalyst and metallic titanium (Ti) mesh as the current collector for electrocatalytic NRR. The as-synthesized AgNDs, homogeneously dispersed in 0.1 M Na2SO4 solution (pH = 10.5), can achieve an NH3 yield rate of 600.4 ± 23.0 μg h−1 mgAg−1 with a faradaic efficiency (FE) of 10.1 ± 0.7% at −0.25 V (vs. RHE). The FE can be further improved to be 20.1 ± 0.9% at the same potential by using Ti mesh modified with oxygen vacancy-rich TiO2 nanosheets as the current collector. Utilizing the aqueous AgNDs catalyst, a Ti plate based two-electrode configured flow-type electrochemical reactor was developed to achieve an NH3 yield rate of 804.5 ± 30.6 μg h−1 mgAg−1 with a FE of 8.2 ± 0.5% at a voltage of −1.8 V. The designed non-loading electrocatalysis system takes full advantage of the AgNDs’ active sites for N2 adsorption and activation, following an alternative hydrogenation mechanism revealed by theoretical calculations.