The electrochemical reduction of CO2 into valuable products at mild reaction conditions and using cheap renewable electrical energy are goals to sustain a low-carbon economy. Among the various CO2 reduction reaction products, formic acid (FA) has received significant attention because of its low Gibbs free energy input requirement and the simple reduction reaction involving the transfer of 2 electrons and 2 protons. In this work, a copper-doped tin oxide catalyst supported on a mesoporous carbon xerogel was shown to enhance the electrochemical reduction of CO2 to formate in a bicarbonate solution coupled with CO2. We observed that the synergistic SnCu oxides enhance the selectivity toward formate from 58.6% for Sn oxide and 28.7% for Cu oxide to over 71.2% for the SnCu oxides. The observed rate of formate production with SnCu oxide was 2.8 times higher compared to the rate of Cu oxide and about 1.5 times higher than with the Sn oxide catalyst. Our results reveal that selectivity for formate comes partly from the electrolysis of the bicarbonate solution and partly from continuous CO2 gas purged into the solution. The contribution from the electrolysis of bicarbonate solution ranges from 15% to 40% when the concentration of bicarbonate solution ranges from 100 mM to 1 M. Chronoamperometric measurements for stability revealed that Cu oxide and Sn oxide showed stable current density for less than 30 h while under the same conditions, the stable current density was observed for more than 50 h with SnCu oxide catalyst. Additionally, the selectivity toward formate increased by 6% when the reactor pressure was increased from near ambient pressure to 4 psig. Our lab-scale electrochemical cell with SnCu oxide supported on the mesoporous carbon xerogel enhances the CO2 solubility, minimizes the precipitation of salts that can degrade the catalytic performance, and suppresses the competitive hydrogen evolution reaction, demonstrating the feasibility of using our catalyst and system for the electrochemical conversion of CO2 into formate with high selectivity, productivity, and stability. This could have significant implications for the mitigation of CO2 emissions and the development of a sustainable chemical industry.

Semiconductor photocatalysis with commercial TiO2 (Degussa P25) has shown significant potential in water treatment of organic pollutants. However, the photoinduced reactions of adsorbed catechol, a phenolic air pollutant from biomass burning and combustion emissions, at the air-solid interface of TiO2 remain unexplored. Herein we examine the photocatalytic decay of catechol in the presence of water vapor, which acts as an electron acceptor. Experiments under variable cut-off wavelengths of irradiation (λcut-off ≥ 320, 400, and 515 nm) distinguish the mechanistic contribution of a ligand-to-metal charge-transfer (LMCT) complex of surface chemisorbed catechol on TiO2. The LMCT complex injects electrons into the conduction band of TiO2 from the highest occupied molecular orbital of catechol by visible light (≥2.11 eV) excitation. The deconvolution of diffuse reflectance UV-visible spectral bands from LMCT complexes of TiO2 with catechol, o-semiquinone radical, and quinone and the quantification of the evolving gaseous products follow a consecutive kinetic model. CO2(g) and CO(g) final oxidation products are monitored by gas chromatography and Fourier-transform infrared spectroscopy. The apparent quantum efficiency at variable λcut-off are determined for reactant loss (Φ- TiO2/catechol = 0.79 ± 0.19) and product growth ΦCO2 = 0.76 ± 0.08). Spectroscopic and electrochemical measurements reveal the energy band diagram for the LMCT of TiO2/catechol. Two photocatalytic mechanisms are analyzed based on chemical transformations and environmental relevance.

The development of an electrochemical catalyst system that converts carbon dioxide (CO2) to high-value chemicals, such as formic acid (FA) will simultaneously curb CO2 emissions to atmosphere and provide sustainable pathways to create a range of fuels at lower cost. Electrochemical conversion of CO2 to FA is a two-electron reduction process and can be carried out at ambient conditions, and the reduced product has been found wide-ranging applications in chemical industries for production of household products, and a safe liquid-phase chemical for hydrogen storage. Synergistic bimetallic electrocatalysts can improve the activity and selectivity over their monometallic counterparts by tuning the structure, morphology, and composition. At the University of Kentucky’s Institute for Decarbonization and Energy Advancement (UK IDEA), our enhanced bimetallic oxide carbon utilization (EBOCU) process uses an engineered catalyst that facilitates operating at relatively low applied potentials, and high product selectivity to produce FA. Using bimetallic tin-copper oxide containing 95 mol% of Sn and 5 mol% of Cu immobilized on mesoporous carbon xerogel and alkaline electrolyte, we observed that hydrogen evolution reaction is suppressed and the selectivity towards formate is enhanced for the cell potential from 3.6 V through 4.0 V. Notably, our electrochemical reactor is successful in converting CO2 to formate at the rate of 2 mM/h in 3 mL/min flow system. Maximum faradaic efficiency of 94% is achieved towards formate at 3.8 V, which remained above 80% even after 200 h of continuous operation.

Electrocatalytic carbon dioxide reduction reaction (CO2RR) technology can simultaneously minimize the CO2 concentration in the atmosphere and generate useful chemicals and fuels. Liquid formic acid (FA) produced from CO2RR is a chemical feedstock for industrial purposes as well as a potential hydrogen storage medium. The downstream separation of liquid FA from the CO2RR effluent increases the total costs in addition to the electrolysis and can also affect the environment adversely. Therefore, efficient, low-cost, and environmentally benign technologies for FA separation from the CO2RR are important for life cycle analysis and techno-economic analysis for this technology. Ion exchange has been proven as an advanced process for FA separation from aqueous solution. This method has attractive due to its high selectivity, low cost, ease of operation and recovery, availability to integrate with other systems, and environmentally benign nature. In this work, three anion exchange resins: Ambersep 900 hydroxide, Amberlite IRA-96 free base, and Amberlite IRA-910 chloride forms have been tested to separate FA from the aqueous solution under varying resin loading (10-60 mg/mL) and initial FA concentration (0.05-0.50 M). The effect of potassium bicarbonate, a commonly used catholyte in electrochemical CO2RR on equilibrium FA adsorption capacity has been investigated with resin loading of 10 and 60 mg/mL under similar initial FA concentrations. Kinetics and equilibrium studies data for the FA adsorption on three resins are interpreted using several kinetics and isotherm models. The kinetics data fits better with pseudo first order at high initial FA concentration and pseudo second order at low initial FA concentration. The results show that the Ambersep 900 hydroxide form with adsorption capacity of 430.8 mg of FA per g of resin is more efficient than the Amberlite IRA-96 free base form (369.9 mg/g) and Amberlite IRA-910 chloride form (291.2 mg/g) in the absence of potassium bicarbonate in the range of parameters studied. However, Amberlite IRA-96 (153.4 mg/g) and Amberlite IRA-910 (143.4 mg/g) can separate FA more efficiently from the potassium bicarbonate aqueous solution than the Ambersep 900 (94.1 mg/g). The experimental data for all resins can be well explained with the Freundlich isotherm model. In the presence of potassium bicarbonate, competitive adsorption of bicarbonate and formic acid reduces the FA adsorption capacity of resins. Experimental and modeling results will be discussed.

Potassium is used extensively as a promoter with iron catalysts in Fisher–Tropsch synthesis, water–gas shift reactions, steam reforming, and alcohol synthesis. In this paper, the identification of potassium chemical states on the surface of iron catalysts is studied to improve our understanding of the catalytic system. Herein, potassium-doped iron oxide (α-Fe2O3) nanomaterials are synthesized under variable calcination temperatures (400–800 °C) using an incipient wetness impregnation method. The synthesis also varies the content of potassium nitrate deposited on superfine iron oxide with a diameter of 3 nm (Nanocat®) to reach atomic ratios of 100 Fe:x K (x = 0–5). The structure, composition, and properties of the synthesized materials are investigated by X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, Fourier-transform infrared, Raman spectroscopy, inductively coupled plasma-atomic emission spectroscopy, and X-ray photoelectron spectroscopy, as well as transmission electron microscopy, with energy-dispersive X-ray spectroscopy and selected area electron diffraction. The hematite phase of iron oxide retains its structure up to 700 °C without forming any new mixed phase. For compositions as high as 100 Fe:5 K, potassium nitrate remains stable up to 400 °C, but at 500 °C, it starts to decompose into nitrites and, at only 800 °C, it completely decomposes to potassium oxide (K2O) and a mixed phase, K2Fe22O34. The doping of potassium nitrate on the surface of α-Fe2O3 provides a new material with potential applications in Fisher–Tropsch catalysis, photocatalysis, and photoelectrochemical processes.

Despite recent literature reporting the remarkable electrochemical CO2 reduction reaction (CO2RR) performance of nitrogen-doped graphitic carbon materials (sp2-carbon) and nitrogen-doped diamond materials (sp3-carbon), no systematic studies have been conducted on the catalytic activities of hybrid carbon nanomaterials between diamond and graphitic extremes. In this study, nitrogen-doped ultra-nanocrystalline diamond thin films were prepared by a microwave-assisted chemical vapor deposition technique. The ratio of sp2-carbon phase to sp3-carbon phase was controlled by varying growth conditions. Our results confirm that nitrogen-doped sp2-carbon (graphitic) rich electrodes have better selectivity for the CO2RR products over the nitrogen-doped sp3-carbon rich electrodes, indicating that the host structure of nitrogen dopants is crucial for the catalytic activity. Nitrogen-doped sp2-carbon electrodes present Faradaic efficiency for CO production up to 82% with excellent activity and selectivity. The vital role of the host structure and the potential catalytic sites were detailed by density functional theory (DFT) calculations.

Fire incident and subsequent evacuation from a pharmaceutical cleanroom facility possess an interesting problem because of the unique operating condition and occupant characteristics that exist in such facility. In the present study, fire and evacuation modelling and safety analysis of a typical pharmaceutical cleanroom facility in Bangladesh is performed. A computational fluid dynamics (CFD) tool PyroSim is used for simulating the fire in the cleanroom and evacuation analysis is performed using a continuous egress modeling software, Pathfinder. In simulating the fire and smoke propagation as well as the evacuation scenario, commonly practiced values, protocols and fuel load characteristics in the pharmaceutical industries of Bangladesh are employed.Two different fire scenarios are considered with a variation in the fuel load and type (ethanol and cardboard), and the location of the origin of the fire. The propagation of smoke and fire, temperature distribution around the cleanroom, concentration of toxic gases and visibility at different sections of the cleanroom are examined. It is found that for the case of the high fuel load in the packaging section in the 1st floor, 12 occupants fail to safely evacuate from the 5-storied pharmaceutical building. The effects of different specific operating characteristics and practices particular to a cleanroom facility on theoccupant evacuationare considered and analyzed.

Heterogeneous photocatalysis is a prominent area of research with major applications in solar energy conversion, air pollution mitigation, and removal of contaminants from water. A large number of scientific papers related to the photocatalysis field and its environmental applications are published in different journals specializing in materials and nanomaterials. However, many problems exist in the conception of papers by authors unfamiliar with standard characterization methods of photocatalysts as well as with the procedures needed to determine photocatalytic activities based on the determination of "apparent quantum efficiencies" within a wavelength interval or "apparent quantum yields" in the case of using monochromatic light. In this regard, an astonishing number of recent research articles include claims of highly efficient (photo)catalysts or similar terms about materials with superior or enhanced efficiency for a given reaction without proper experimental support. Consequently, the comparison of the efficiencies of photocatalysts may result as being meaningless, especially when reports are only based on expressions determining (1) a reaction rate per weight of catalyst or its surface area, (2) quantum efficiencies or quantum yields, and (3) turnover frequencies or turnover numbers. Herein, we summarize the standards needed for reporting valuable data in photocatalysis and highlight some common discrepancies found in the literature. This work should inform researchers interested in reporting photocatalysis projects about the correct procedures for collecting experimental data and properly characterizing the materials by providing examples and key supporting literature.

In this work, highly active and stable platinum-palladium core-shell nanoflowers supported on sulfur-doped graphene (PtPd-NF/SG) with a polyol reduction method are synthesized. Platinum is decorated on palladium seeds to form core-shell structured floral petals to improve surface activity and give high electrochemically active surface area and stability. The catalyst is deposited on sulfur-doped graphene to induce highly favorable catalyst-support interactions to ensure long-term electrochemical stability. The specific activity and mass activity of the synthesized core-shell nanocatalysts are 3.2 and 4.7 times higher than commercial Pt/C toward oxygen reduction reaction, respectively. After 10 000 testing cycles, the mass and specific activity of the catalyst is approximate to 25 and approximate to 18 times higher than the Pt/C benchmark catalyst, respectively. The enhanced electrochemical activity and excellent stability of PtPd-NF/SG can be attributed to the 2D core-shell nanoflower structure, weak binding of hydroxyl groups to the platinum metal deposited on palladium, and robust sulfur-doped graphene support.

Development of highly durable electrocatalysts for oxygen reduction reaction (ORR) is critical for proton exchange membrane fuel cells. Herein, we report the synthesis, characterization, and electrochemical performance of 1D sulfur-doped carbon nanotubes (S-CNT) supported 1D Pt nanowires (PtNW/S-CNT). PtNW/S-CNT synthesized by a modified solvothermal method possesses a unique web-like 3D architecture that is beneficial for oxygen reduction. We demonstrate that PtNW/S-CNT exhibits impressive activity retention under potential cycling between 0.05 and 1.5 V vs RHE over 3000 cycles. The reductions in electrochemically active surface area (ECSA, 7% loss) and mass activity (19% loss) of PtNW/S-CNT after accelerated durability testing (ADT) are found to be much lower than the dramatic losses observed with commercial Pt/C (>99% loss in ECSA and mass activity) under identical conditions. The PtNW/S-CNT catalyst also shows very high specific activity (1.61 mA cm–2) in comparison to Pt/C (0.24 mA cm–2).

Rich, porous graphene frameworks decorated with uniformly dispersed active sites are prepared by using polyaniline as a graphene precursor and introducing phenanthroline as a pore-forming agent. The unprecedented fuel-cell performance of this electrocatalyst is linked to the graphene frameworks with vast distribution of pore sizes, which maximizes the active-sites accessibility, facilitates mass-transport properties, and improves the carbon corrosion resistance.

Post-heat treatment of dealloyed Pt–Ni nanoparticles on sulfur-doped graphene for PEM fuel cell cathode catalysis exhibit greatly improved activity and electrochemically active surface area retention over Pt/C in half-cell conditions.

Nitrogen-functionalized graphene materials have been demonstrated as promising electrocatalyst for the oxygen reduction reaction (ORR), owning to their respectable activity and excellent stability in alkaline electrolyte. However, they exhibit unacceptable catalytic activity in acid medium. Here, a hierarchically porous Co-N functionalized graphene aerogel is prepared as an efficient catalyst for the ORR in acid electrolyte. In the preparation process, polyaniline (PANI) is introduced as a pore-forming agent to aid in the self-assembly of graphene species into a porous aerogel networks, and a nitrogen precursor to induce in situ nitrogen doping. Therefore, a Co-N decorated graphene aerogel framework with a large surface area (485 m(2) g(-1)) and an abundance of meso/macropores is effectively formed after heat treatment. Such highly desired structures can not only expose sufficient active sites for the ORR but also guarantee the fast mass transfer in the catalytic process, which provides significant catalytic activity with positive onset and half wave potentials, low hydrogen peroxide yield, high resistance to methanol crossover, and remarkable stability that is comparable to commercial Pt/C in acid medium.

An electrically rechargeable, nanoarchitectured air electrode that morphologically emulates a human hair array is demonstrated in a zinc-air battery. The hair-like array of mesoporous cobalt oxide nanopetals in nitrogen-doped carbon nanotubes is grown directly on a stainless-steel mesh. This electrode produces both flexibility and improved battery performance, and thus fully manifests the advantages of flexible rechargeable zinc-air batteries in practical applications.

Heat treated iron-polyaniline-carbon – based non-precious metal catalysts represent a promising class of material to replace the platinum based ORR catalysts for PEMFC technologies. In the present research, we apply an ammonia treatment to tune the structure and activity of electrocatalysts derived from iron, polyaniline and carbon nanotubes (CNTs). By controlling the NH3 reaction conditions, we were able to tune the chemistry of nitrogen incorporation, including concentration and dopant type. The final catalyst had a robust morphology consisting of highly porous 2-D in-situ formed graphene-like structures that, along with the intermixed 1-D CNTs, were decorated with an abundance of nitrogen and iron species. The resultant surface chemistry led to impressive catalyst activity, with a half-wave potential of 0.81 V observed through half-cell testing and under H2-air fuel cell testing, a current density of 77 mA cm−2 at 0.8 V was achieved, along with a maximum power density of 335 mW cm−2.

Tremendous research interest from both academy and industry has been dedicated to the rechargeable lithium-ion batteries (LIBs) in the last decades for the upcoming era of portable electronics, electric vehicles (EVs) and hybrid electric vehicles (HEVs). As one of the favorite power sources, most commercial LIBs utilize natural or synthetic graphite as the anode material due to its low cost, high Coulombic efficiency, and flat and low average potential of 0.2 V (vs. Li/Li+), as well as long cycle life. However, its specific capacity of 372 mA h g-1 results in a device energy density of ~150 W h kg-1, which is much lower than that of internal-combustion engines and cannot meet the EVs requirements. Therefore, there is an urgent need to develop novel anode materials with high theoretical capacities to replace graphite in next generation high energy LIBs. So far, various materials have been extensively studies for LIBs anodes, including alloys (e.g. Si and Sn) and transition metal oxides (e.g. Li4Ti5O12 and SnO2). Although most of these materials possess a significant larger specific capacity, they suffer from either poor cycling life due to volume change associated with Li-ion insertion/extraction or sluggish electrode kinetics stemmed from slow ion diffusivity or intrinsic poor electron conductivity. Compared to metal oxide materials, some transition metal sulfides possess high specific capacity and unique structures, and have been considered as promising candidates for high-performance anode materials. Among various candidates, a typical member of transition metal sulfide-molybdenum disulfide (MoS2) possesses a similar layered structure to graphite but a much larger interlayer spacing of 6.15 Å (vs. 3.35 Å of graphene) by stacking together through van der Waals interactions, which facilitates lithium-ion intercalation without a significant volume expansion. However, MoS2 still suffers from fast structural deterioration during lithiation/de-lithiation process and poor electrical/ionic conductivity, resulting in unsatisfactory cycling performance and rate capability in LIBs application. Therefore, the development of novel highly stable MoS2-based materials with fast kinetics remains challenging, owing to the lack of a ration design from molecular level. Moreover, it is also critical to correlate the performance with materials structure, and to understand the chemistry behind before its future practical applications. Herein, we demonstrate a facile solvothermal synthesis of nanocomposites consisting few-layered MoS2 and covalently sulfur-doped graphene (MoS2/SG) with excellent electrochemical performance. We focus on not only the development of MoS2-based electrode materials but also the materials design based on both structure and chemistry considerations. The sulfur atoms covalently bonded to graphene sheets and effectively bridging two-dimensional (2D) few-layered MoS2 and graphene enable high robustness of the composite materials. Moreover, the intimate contact of MoS2 and highly conductive graphene provides efficient electron transfer pathways, while the high surface of assembled 2D structured materials allows fast access to active materials. Such a unique composite architecture derived from the “bridging effect” ensures the electrode with an exceptional cycling stability and superior rate capability, which is also interpreted by the density functional theory (DFT) calculations. A capacity retention of 92.3% can be achieved after 2000 cycles at a current density of 10 A g-1; even at a high current density of 20 A g-1, the electrode still possesses a specific capacity of 766 mA h g-1. This composite material with excellent electrochemical properties synthesized via a facile solvo-thermal approach holds great promise in the practical application of high-performance LIBs. Figure 1

The slow kinetics of the oxygen reduction reaction (ORR) on platinum catalyst is a critical parameter for application in polymer electrolyte membrane fuel cells (PEMFCs). Herein, we study the effects of sulfur on the electrochemical activity and stability of sulfur doped graphene supported platinum nanowires (PtNW/SGs). To investigate the influence of sulfur, a series of sulfur-doped graphene materials with varying sulfur contents ranging from 0.35 to 3.95at% are applied as platinum nanowire catalyst supports. Based on the physico-chemical characterizations, electrochemical measurements and density functional theory (DFT) calculations, we find that the amount of sulfur significantly affects the electrokinetics of the Pt nanowires. The best ORR kinetics are observed for the platinum nanowires supported on graphene with 1.40at% sulfur, showing a mass activity of 182mA/mgPt and a specific activity of 662μA/cm2Pt at 0.9V vs. RHE. At this sulfur content, well-defined platinum nanowires with diameters in the range of 4–16nm are observed that are beneficial for enhancing ORR kinetics.

Grain boundaries are revealed to be a primary source of one-dimensional Pt nanostructure instability by comparing the structural evolution processes of rationally synthesized tubular structures with Pt/C.

Unique tin oxide-mesoporous carbon (SnO2-CMK-3) composites have been synthesized as platinum nanoparticle electrocatalyst supports for low temperature fuel cell applications. In comparison with state-of-the-art commercial carbon-supported platinum (Pt/C) and pure CMK-3-supported platinum (Pt/CMK-3), Pt/SnO2-CMK3 demonstrated improved Pt-mass and surface area based ethanol oxidation reaction (EOR) activity through half-cell electrochemical investigations, providing a 64.7 and 97.6 mV reduction in overpotential at 100 mA mg−1Pt upon comparison to Pt/CMK-3 and commercial Pt/C. Furthermore, improvements to the oxygen reduction reaction (ORR) kinetics were observed, with Pt/SnO2-CMK3 providing a kinetic current density of 3.40 mAcm−2 at an electrode potential of 0.9 V vs RHE. The improved performance of Pt/SnO2-CMK-3 for EOR and ORR was attributed to the beneficial impact of the support properties, along with potential interactions occurring between the support and catalyst particles. Complemented by extensive physicochemical characterization, these unique materials show high promise for application in low temperature fuel cells.