Reduction Reaction Applications Research Articles

Flatland materials for photochemical and electrochemical nitrogen fixation applications: from lab-door experiments to large-scale applicability

Flatland materials were meticulously surveyed to explore their functionality in photochemical and electrochemical nitrogen reduction reaction applications. New insights are presented for pilot-scale NRR operations via 2D materials.

The Effect of SnO2 Surface Properties on CO2 Photoreduction to Higher Hydrocarbons

AbstractSeveral photocatalysts have been developed for applications in reduction reactions, including tin oxide‐based semiconductors. Although its band structure is unfavorable for CO2 reduction reactions, strategies to modify its surface properties directly impacted its activity and selectivity during these reactions. Here, we analyze the influence of heat treatment and decoration of SnO2 with gold nanoparticles on the gas phase CO2 photoreduction process. In both cases, a deleterious effect was observed during reactions under UV radiation (with a drop of 59.81 % and 51.45 % in CH4 production for SnO2_150 °C and SnO2/Au_cop, respectively, compared to SnO2_cop), which is directly related to the availability of surface hydroxyl groups that play a crucial role in CO2 adsorption. Under visible radiation, the gold plasmonic resonance took place in the production of methane (0.33 μmol g−1 for SnO2/Au_cop and 0.29 μmol g−1 for SnO2/Au_150 °C), with small amounts of carbon monoxide (0.06 μmol g−1 for SnO2/Au_cop and 0.03 μmol g−1 for SnO2/Au_150 °C). These results demonstrate that, though the SnO2 band structure does not indicate a good semiconductor for CO2 reduction, its surface characteristics are responsible for its catalytic activity.

Advances in Designing 3D‐Printed Systems for CO2 Reduction

AbstractThe increasing level of atmospheric carbon dioxide (CO2), and the resultant global warming is a matter of growing concern among scientists, environmentalists, and climate experts across the globe over the past several decades. Numerous attempts are being undertaken today that seek solutions to mitigate this global crisis. This includes designing functional catalysts, devices and reactors to convert greenhouse gasses such as CO2 into useful products like low‐carbon fuels and chemicals, thereby reducing the amount of CO2 considerably in the atmosphere. Advancements in emerging technologies like 3D‐printing can effectively aid in the fabrication of electrodes and devices to tackle the rising CO2 concerns. Low cost, rapid prototyping ability, and printing simple and complex structure are few of the significant merits of this technology. Thus, in this perspective article, discussions on fabricating 3D‐printed (electro)catalysts, customized devices, reactors, etc., via multiple strategies are put forward with emphasis on the electrochemical reduction of CO2. Also, a detailed discussion on the post‐printing treatments, catalyst modifications, and other CO2 mitigation strategies is provided as well. Although studies in this direction are scarcely reported, observations made hitherto show promising possibilities of broadening this field for large scale CO2 reduction reaction applications, and similar catalytic applications in the near future.

Physicochemical and optical studies of novel heterogeneous oxysulfide catalyst based on Mo for potential application in reduction reactions

In this study, a series of Mo-M binary oxysulfides catalysts (M = Ni, Co, Fe and Ce) were fabricated using a simple one-pot process. The oxysulfides were characterized using XPS, XRD, TEM-EDS, SBET, FTIR and UV–vis/DR spectroscopy. The oxysulfides catalysts applied for reduction and decolorization of organic pollutants like MB, RR, MO and 4NP in the presence of NaBH4. All the synthesized oxysulfides improved the reduction and decolorization of organic pollutants and the order was MoNi > MoCo > MoFe > MoCe. The highest reduction activity of MoNi oxysulfide is due to the highest surface area which facilitates the adsorption of pollutants and the small band gap which facilitates the transferring of an electron. The reusability of MoNi was also investigated. The results showed that the oxysulfide is stable and reused successfully four times. Hence, it is considered a favorable substance for potential applications.

The electronegativity modulation of rutile TiO2 nanorods by phosphate and its photocatalytic hydrogen production performance

In this paper, PO was grafted on the surface of rutile TiO2 by one-step hydrothermal method. Due to the presence of the highly electronegative oxygen element, the surface of TiO2 often presented an electron-deficient state, which limited its application in reduction reactions. Herein, the low electronegativity element P from the phosphate was grafted on the surface of TiO2 to form a PO structure, which changes the electronic equilibrium state of the TiO2 and provide a new channel for electron migration. The surface of TiO2 presented an electron-enrich structure, which promoted the best hydrogen production performance around 28 mmol·g−1·h−1 on TiO2-P-0.01.

Predicted Electrocatalyst Properties on Metal Insulator MoTe2 for Hydrogen Evolution Reaction and Oxygen Reduction Reaction Application in Fuel Cells

Systematic spin-polarized density functional theory (DFT) calculations were executed to study the catalytic performance of the topological insulator MoTe2 (2H, 1T, and 1T′) phase. Topological insul...

Fabrication and Characterization of Metal‐Free Composite Electrodes Based on Few‐Layer‐Graphene Nanoplatelets for Oxygen Reduction Reaction Applications

The fabrication of advanced graphene‐based electrodes is currently an open research topic because of their potential in a broad range of applications, such as in light‐emitting diodes, field‐effect transistors, solar cells, supercapacitors, batteries, electrochemical energy storage, and sensors, which can be traced back to their remarkable electronic, mechanical, optical, and thermal properties. Herein, the fabrication and characterization of metal‐free few layer graphene‐based composite electrodes for oxygen reduction reaction (ORR) applications is reported. Electrodes’ characterization and performance are assessed using Raman spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The electrocatalytic activity for ORR is elucidated by determination of the reaction onset potential at different pH values. The best formulation shows cathodic peak current density up to −469 μA cm−2, accompanied by the lowest potential peak separation of 0.17 V and the lowest charge transfer resistance of 1657 Ω cm−2, which is almost five times lower if compared with the composite electrode without graphene. The results suggest that similar nanocomposites electrodes might be potentially exploited in life processes such as biological respiration, and in energy converting systems such as fuel cells or microbial fuel cells.

Three-Dimensional-Order Macroporous AB2O4 Spinels (A, B =Co and Mn) as Electrodes in Zn-Air Batteries.

In this work, atomically substituted three-dimensionally ordered macroporous (3DOM) spinels based on Co and Mn (MnCo2O4 and CoMn2O4) were synthetized and used as cathodic electrocatalysts in a primary Zn-air battery. Scanning/transmission electron microscopy images show a 3DOM structure for both materials. Skeleton sizes of 114.4 and 140.8 nm and surface areas of 65.3 and 74.6 m2 g-1 were found for MnCo2O4 and CoMn2O4, respectively. The increase in surface area and higher presence of Mn3+ and Mn4+ species in the CoMn2O4 3DOM material improved battery performance with a maximum power density of 101.6 mW cm-2 and a specific capacity of 1440 mA h g-1, which shows the highest battery performance reported to date using similar spinel materials. The stability performance of the electrocatalyst was evaluated in half-cell and battery cell systems, showing the higher durability of CoMn2O4, which was related to its better capability to perform the electrocatalytic process as adsorption, electron transfer, and desorption. It was found through density functional theory calculations that the CoMn2O4 spinel has a higher density of states in the Fermi level vicinity and better conductivity. Finally, the unique shape of 3DOM spinels promoted a high interaction between electroactive species and catalytic sites, making them suitable for oxygen reduction reaction applications.

Enhancing bioelectricity generation of bio-electrochemical reactors using porous nickel-based composite as effective oxygen reduction catalyst

Microbial fuel cell as a sustainable microbial-electrochemical reactor can harvest bio-power from wastewater by the oxidation of electro-active bacteria on the anode, while its power output is greatly relying on the oxygen reduction reaction performance of the cathode electro-catalysts. Here, the dahlia flower-like nickel-based composites have been synthesized through a hydrothermal reaction, and was used as an efficient oxygen reduction reaction catalyst in a single chamber microbial fuel cell. The physical characterization of surface structure suggests the composites have successfully prepared. The MFC with Ni-melamine cathode can achieve obviously higher power density of 378.08 mW m−2 than those of Ni-urea cathode (244.02 mW m−2) and Ni-dicyandiamide cathode (201.67 mW m−2). A series of electrochemical characterization suggests that Ni-melamine electrode possesses larger electrochemical active surface area, lower charge transfer resistance, and higher oxygen reduction performance than those of Ni-urea electrode and Ni-dicyandiamide electrode. The electrochemical measurements have also demonstrated that nickel-melamine composites can be involved in oxygen reduction reaction via a four-electron route due to the high-efficient electrocatalytic activity. In addition, the maximum power density of nickel-based composites is obviously increased with an increase of catalysts coating amounts. When the loading amounts are 4 mg cm−2, the power density for nickel-based composites is improved to 1421.4 mW m−2, which is 1.68 times higher than that of Pt/C due to the introduction of oxygen vacancies and nitrogen element. Thus, nickel-based composite is an effective and promising catalyst material for microbial fuel cell to substitute Pt/C for oxygen reduction reaction application.

Nitrogen and high oxygen-containing metal-free porous carbon nanosheets for supercapacitor and oxygen reduction reaction applications

Herein, the synthesis of heteroatom-containing graphene-like carbon nanosheets (HA-GCNs) by chemical activation of waste biomass, namely peanut shells. As characterized by a variety of analytical and spectroscopy techniques, the as-synthesized HA-GCNs material carbonized at 900 °C was found to possess sheet-like porous nanosheet morphology with high surface areas (>800 m2 g−1) and desirable of heteroatom contents such as nitrogen (N; 0.84 atom%), and oxygen (O) as high as 20.25 atom%, which greatly improved the electronic properties of the carbon substrate for prospective applications as metal-free electrodes and electrocatalytic materials. The HA-GCNs were found to exhibit a superior specific capacitance of 148, 145, 125, and 105 F g−1 corresponding to the KOH, NaOH, LiOH, and H2SO4 electrolyte solutions, respectively. Although, the HA-GCNs electrode exhibited extraordinary electrochemical performances and cyclic charge-discharge stabilities. Moreover, these novel HA-GCNs exhibited excellent electrocatalytic activities and cyclic stabilities for oxygen reduction reaction (ORR) with a desirable current density of 1.17 mA cm−2 in O2-saturated 0.1 M KOH solution, surpassing that of noble metal-incorporated activated carbons. The superior electrochemical and electrocatalytic performances observed for the HA-GCNs were attributed to the unique pseudocapacitive behavior of the oxygen surface functional groups as well as their unique textural properties, rendering practical applications as low-cost electrodes for supercapacitors and metal-free electrocatalysts for ORR.

Carbon Xerogels Hydrothermally Doped with Bimetal Oxides for Oxygen Reduction Reaction.

A total of two carbon xerogels doped with cobalt and nickel were prepared by the sol–gel method. The obtained carbon xerogels underwent further surface modification with three binary metal oxides namely: nickel cobaltite, nickel ferrite, and cobalt ferrite through the hydrothermal method. The mesopore volumes of these materials ranged between 0.24 and 0.40 cm3/g. Moreover, there was a morphology transformation for the carbon xerogels doped with nickel cobaltite, which is in the form of nano-needles after the hydrothermal process. Whereas the carbon xerogels doped with nickel ferrite and cobalt ferrite maintained the normal carbon xerogel structure after the hydrothermal process. The prepared materials were tested as electrocatalysts for oxygen reduction reaction using 0.1 M KOH. Among the prepared carbon xerogels cobalt-doped carbon xerogel had better electrocatalytic performance than the nickel-doped ones. Moreover, the carbon xerogels doped with nickel cobaltite showed excellent activity for oxygen reduction reaction due to mesoporosity development. NiCo2O4/Co-CX showed to be the best electrocatalyst of all the prepared electrocatalysts for oxygen reduction reaction application, exhibiting the highest electrocatalytic activity, lowest onset potential Eonset of −0.06 V, and the lowest equivalent series resistance (ESR) of 2.74 Ω.

Boost-up electrochemical performance of MOFs via confined synthesis within nanoporous carbon matrices for supercapacitor and oxygen reduction reaction applications

The electrochemical performance of MOFs for supercapacitor and oxygen reduction reaction applications is significantly improved when conjugated with conductive and 3D connected nanoporous carbon matrices.

Hierarchical Heterostructures of Ultrasmall Fe2O3-Encapsulated MoS2/N-Graphene as an Effective Catalyst for Oxygen Reduction Reaction.

In this study, a facile approach has been successfully applied to synthesize a hierarchical three-dimensional architecture of ultrasmall hematite nanoparticles homogeneously encapsulated in MoS2/nitrogen-doped graphene nanosheets, as a novel non-Pt cathodic catalyst for oxygen reduction reaction in fuel cell applications. The intrinsic topological characteristics along with unique physicochemical properties allowed this catalyst to facilitate oxygen adsorption and sped up the reduction kinetics through fast heterogeneous decomposition of oxygen to final products. As a result, the catalyst exhibited outstanding catalytic performance with a high electron-transfer number of 3.91-3.96, which was comparable to that of the Pt/C product. Furthermore, its working stability with a retention of 96.1% after 30 000 s and excellent alcohol tolerance were found to be significantly better than those for the Pt/C product. This hybrid can be considered as a highly potential non-Pt catalyst for practical oxygen reduction reaction application in requirement of low cost, facile production, high catalytic behavior, and excellent stability.

Highly active and reducing agent-free preparation of cost-effective NiO-based carbon nanocomposite and its application in reduction reactions under mild conditions

Highly efficient and cost-effective NiO-based carbon nanocomposite (NiO/CNP) was prepared for the transfer hydrogenation of aromatic aldehydes and reduction of nitrophenols. Uniform dispersion of NiO nanoparticles, surface area of NiO/CNP (67m2g−1), chemical state and content of Ni in NiO/CNP (+2, 5.1wt%) were confirmed. High rate constant (kapp) values of 4.2×10−2s−1 and 3.06×10−2s−1 were calculated for the NiO/CNP–catalyzed reduction of nitrophenols. The NiO/CNP demonstrated an excellent catalytic activity towards the transfer hydrogenation reactions under very mild reaction conditions. Chemoselectivity, heterogeneity, stability, reusability and scale reaction of the NiO/CNP system were tested.

Uniform, Nitrogen and Sulfur Codoped Carbon Nanospheres for Oxygen Reduction Reaction Application

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Nitrogen-doped graphene prepared by a transfer doping approach for the oxygen reduction reaction application

Well defined nitrogen-doped graphene (NG) is prepared by a transfer doping approach, in which the graphene oxide (GO) is deoxidized and nitrogen doped by the vaporized polyaniline, and the GO is prepared by a thermal expansion method from graphite oxide. The content of doped nitrogen in the doped graphene is high up to 6.25 at% by the results of elements analysis, and oxygen content is lowered to 5.17 at%. As a non-precious metal cathode electrocatalyst, the NG catalyst exhibits excellent activity toward the oxygen reduction reaction, as well as excellent tolerance toward methanol. In 0.1 M KOH solution, its onset potential, half-wave potential and limiting current density for the oxygen reduction reaction reach 0.98 V (vs. RHE), 0.87 V (vs. RHE) and 5.38 mA cm−2, respectively, which are comparable to those of commercial 20 wt% Pt/C catalyst. The well defined graphene structure of the catalyst is revealed clearly by HRTEM and Raman spectra. It is suggested that the nitrogen-doping and large surface area of the NG sheets give the main contribution to the high ORR catalytic activity.

Electrochemical kinetics and X-ray absorption spectroscopy investigations of select chalcogenide electrocatalysts for oxygen reduction reaction applications

Transition metal-based chalcogenide electrocatalysts exhibit a promising level of performance for oxygen reduction reaction applications while offering significant economic benefits over the state of the art Pt/C systems. The most active materials are based on Ru x Se y clusters, but the toxicity of selenium will most likely limit their embrace by the marketplace. Sulfur-based analogues do not suffer from toxicity issues, but suffer from substantially less activity and stability than their selenium brethren. The structure/property relationships that result in these properties are not understood due to ambiguities regarding the specific morphologies of Ru x S y -based chalcogenides. To clarify these properties, an electrochemical kinetics study was interpreted in light of extensive X-ray diffraction, scanning electron microscopy, and in situ X-ray absorption spectroscopy evaluations. The performance characteristics of ternary M x Ru y S z /C (M = Mo, Rh, or Re) chalcogenide electrocatalysts synthesized by the now-standard low-temperature nonaqueous (NA) route are compared to commercially available (De Nora) Rh- and Ru-based systems. Interpretation of performance differences is made in regards to bulk and surface properties of these systems. In particular, the overall trends of the measured activation energies in respect to increasing overpotential and the gross energy values can be explained in regards to these differences.

X-ray Absorption Spectroscopy Investigations of Transition Metal-based Chalcogenide Electrocatalysts for Oxygen Reduction Reaction Applications

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Peroxide Yields and Activation Energies of Select Chalcogenide Systems for Oxygen Reduction Reaction Applications

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