Catalytic Activity In Alkaline Solution Research Articles

Cobalt nanoparticles supported on nitrogen-doped carbon nanotubes for the efficient oxygen reduction reaction in Mg-air battery

Fabricating the non-precious-metal catalyst with desirable catalytic performance towards oxygen reduction reaction (ORR) is essential for Mg-air battery that adopts neutral brine electrolyte. However, the classic metal-nitrogen-carbon materials with strong ORR catalytic activity in alkaline solution usually display inferior performance than platinum-based catalysts in neutral environment. Herein, we construct a hybrid catalyst composed of cobalt nanoparticles and nitrogen-doped carbon nanotubes, based on pyrolyzing the mixture of melamine, pyrazole, hexadecyl trimethyl ammonium bromide, and 2-methylimidazole chelated with Co2+ and Zn2+ ions. This catalyst possesses abundant ORR catalytic active sites and mesoporous structure with large pore volume, which can result in the superior performance of Mg-air battery than that using Pt/C catalyst. Furthermore, its ORR catalytic mechanism is unraveled according to microstructure characterization and electrochemical response.

Preparation of Co-W-P-O/NF catalyst with crystalline-amorphous phase structure by electrodeposition and study on its water splitting properties

The development of renewable clean energy is imminent as global warming and environmental pollution become more serious issues today. Hydrogen energy has been widely studied as an ideal green energy source. Among several common hydrogen production methods, hydrogen production by electrolysis of water is considered an efficient, environmentally friendly, and sustainable hydrogen production strategy. Transition metal phosphates have outstanding electrocatalytic conductivity and high catalytic efficiency, thus exhibiting catalytic effects similar to noble metals. To further enhance the catalytic activity of the transition metal phosphates, in this paper, the cauliflower-like Co-W-P-O4/NF catalyst based on three-dimensional nickel foam was prepared by the method of element doping. The catalyst exhibited good bifunctional catalytic activity in alkaline solution. The prepared Co-W-P-O4/NF has a unique crystalline-amorphous phase structure with abundant active sites at the interface. In addition, W atoms can interact with Co atoms to co-optimise the electronic structure, enabling the Gibbs free energy of hydrogen adsorption (ΔGH*) to be close to 0, which is conducive to improving the performance of water electrolysis. To achieve a current density of 10 mA·cm−2, the Co-W-P-O4/NF required overpotentials of 42.1 mV for HER and 348.2 mV for OER in 1 M KOH solution, with the Tafel slopes being 48.0 and 83.6 mV·dec−1, respectively. When Co-W-P-O4/NF was used as both cathode and anode for water splitting, the two-electrode electrolyzer could achieve 10 mA·cm−2 with only 1.62 V, along with good stability.

Dual-cation-doped MoS2 nanosheets accelerating tandem alkaline hydrogen evolution reaction

Molybdenum disulfide (MoS2) nanosheets are promising candidates as earth-abundant and low-cost catalyst for hydrogen evolution reaction (HER). Nevertheless, compared with the benchmark Pt/C catalyst, the application of MoS2 nanosheets is limited to its relatively low catalytic activity, especially in alkaline environments. Here, we developed a dual-cation doping strategy to improve the alkaline HER performance of MoS2 nanosheets. The designed Ni, Co co-doped MoS2 nanosheets can promote the tandem HER steps simultaneously, thus leading to a much enhanced catalytic activity in alkaline solution. Density functional theory calculations revealed the individual roles of Ni and Co dopants in the catalytic process. The doped Ni is uncovered to be the active site for the initial water-cleaving step, while the Co dopant is conducive to the H desorbing by regulating the electronic structure of neighboring edge-S in MoS2. The synergistic effect resulted by the dual-cation doping thus facilitates the tandem HER steps, providing an effective route to raise the catalytic performance of MoS2 materials in alkaline solution.

Electrochemical properties of AB5 type La0.8Ce0.2Ni4Co0.5Mn0.3Al0.2 alloy for unified metal hydride fuel cell

Metal hydride materials are widely applied for electrochemical energy storage. AB5 type alloys are the main anode material for Ni-MH batteries. Reversible hydrogen uptake and release provides good opportunities to use metal hydrides for alkaline fuel cell applications. Metal hydrides have good activation performance, high hydrogen sorption/desorption rates, catalytic activity in alkaline solution. Current work presents the first experimental results of AB5 type metal hydride electrodes, measured in a battery mode. The electrochemical properties of the prepared electrodes, such as activation performance, maximum discharge capacity, and high rate dischargeability are investigated in detail.

On the Origin of the Effect of pH in Oxygen Reduction Reaction for Nondoped and Edge-Type Quaternary N-Doped Metal-Free Carbon-Based Catalysts.

Metal-free carbon-based catalysts have gained much attention during the last 15 years as an alternative toward the replacement of platinum-based catalysts for the oxygen reduction reaction (ORR). However, carbon-based catalysts only show promising catalytic activity in alkaline solution. Concurrently, the most optimized polymer electrolyte membrane fuel cells use proton exchange membranes. This means that the cathode electrode is surrounded by a protonic environment in which carbon materials show poor performance, with differences above 0.5 V in EONSET for nondoped carbon materials. Therefore, the search for highly active carbon-based catalysts is only possible if we first understand the origin of the poor electrocatalytic activity of this kind of catalysts in acidic conditions. We address this matter through a combined experimental and modeling study, which yields fundamental principles on the origin of the pH effects in ORR for carbon-based materials. This is relevant for the design of pH-independent metal-free carbon-based catalysts.

High surface area for La1-xSrxFeO3 (x=0, 0.4, 0.6) as bifunctional catalyst for rechargeable Li-O2 batteries

Three-dimensionally mesoporous La1-xSrxFeO3 (x = 0, 0.4, 0.6) precursors have been synthesized through a facile solvothermal process. After high-temperature sintering, La1-xSrxFeO3 still exhibits uniform morphology and good dispersibility, which provides a porous structure and favorable surface area. Particularly, La0.4Sr0.6FeO3 shows the biggest surface area of 58 m2 g−1. Doping also induces the generation of oxygen vacancies and Fe4+, which is beneficial for the conductivity and catalytic activity of the materials. Complete with favorable structure and electrochemical activity, La0.4Sr0.6FeO3 exhibits bifunctional catalytic activity in alkaline solution. Applied as a cathode catalyst in Li-O2 batteries, it shows a larger discharge capacity of 23 905 mA h g−1 and a better cycling stability of 100 cycles.

Excellent Fenton-like catalyst application in alkaline solution

Fenton process has been widely applied for environmental restoration. However, acidic and neutral solutions are always needed in order to obtain an excellent catalytic activity. Flower-like MoS2 was firstly used as a Fenton catalyst with higher activity in alkaline solution than that in acidic and neutral ones. The catalytic mechanism indicated that [Formula: see text] and [Formula: see text] radicals formation induced the excellent catalytic activity in alkaline solution. Effects of pH, catalyst dosage, H2O2 and RhB concentrations on catalytic activity were studied, and the quantitative relations were established. The experimental result demonstrated that the catalyst was stable in alkaline solution. The leaching Mo was smaller than 2[Formula: see text]mg/L.

Electrochemical Decomposition of Wheat Straw Lignin into Guaiacyl‐, Syringyl‐, and Phenol‐Type Compounds Using Pb/PbO2 Anode and Alloyed Steel Cathode in Alkaline Solution

An electrocatalytic method was applied to decompose unit structures of wheat straw lignin (WSL) through oxidation on Pb/PbO2 and reduction on alloyed materials cathode with different catalytic activity in alkaline solution. Six of guaiacyl‐type (G) compounds were chosen as target products for evaluating their properties and efficiencies of all selected cathodes in WSL decomposition. A series of alloyed materials were examined as catalysts for the electrocatalytic decomposition, thereinto, the selected catalysts were characterized and evaluated by a systematic study for hydrogenation of WSL in NaOH solution. The effects of reaction parameters, such as pH, current density, lignin concentration and temperature, on product yields were investigated. Gas chromatography (GC) monitored maximum yields of 1.134 and 1.248 g/kg‐lignin of guaiacol and acetovanillone using FeW9Cr4V5Co3 as cathode, 0.364, 3.797, and 1.147 g/kg‐lignin of 4‐ethylguaiacol, vanillin, and vanillyl acetone using 304 alloyed steel as cathode, 1.040 g/kg‐lignin of 4‐propyl guaiacol using FeW9Cr4Mo3V as cathode, respectively. Based on the maximum yield of guaiacyl‐type compounds, 304 alloyed steel gave the best results with respect of lignin decomposition at the optimum conditions. In addition, gel permeation chromatography (GPC) demonstrated that the average molecular weights (Mw) of the lignin decreased in the process of all reactions and the unit structures cut down from lignin were electro‐catalytically hydrogenated to guaiacyl‐, syringyl‐, and phenol‐type compounds. © 2018 American Institute of Chemical Engineers Environ Prog, 38:e13117, 2019

Significantly enhanced oxygen reduction activity of Cu/CuNxCy co-decorated ketjenblack catalyst for Al–air batteries

Highly efficient and non-precious catalysts are imperative for oxygen reduction reaction (ORR) to replace Pt/C. Anchoring efficient active species to carbon supports is a promising and scalable strategy. Here we synthesize Cu nanoparticles and noncrystalline CuNxCy species co-decorated ketjenblack (KB) carbon catalyst (denoted as Cu-N-KB-acid) by a facile and scalable method using copper sulfate, melamine, and KB as raw materials. An initial one-pot hydrothermal treatment is designed before pyrolysis process to achieve the good distribution of Cu and melamine on KB via a possible chelation effect. Owing to the synergistic effect of Cu and CuNxCy on KB, this composite catalyst displays excellent ORR catalytic activity in alkaline solution, which is comparable to the commercial 20% Pt/C. When used as a catalyst in a home-made Al–air battery, it shows a stable discharge voltage of 1.47 V at a discharge density of 50 mA cm−2, a little higher than that of Pt/C (1.45 V).

NiMoS3 Nanorods as pH-Tolerant Electrocatalyst for Efficient Hydrogen Evolution

To meet the increasing demands for sustainable and clean hydrogen energy sources, development of pH-tolerant electrocatalysts with high-performance and low-cost toward hydrogen evolution reaction (HER) is an important but challenging task. MoS2 is postulated as a promising candidate for HER in acidic solution, however, showing poor activity in alkaline media. Herein, to widen its application in various media, we first report the synthesis of NiMoS3 nanorods using a hydrothermal method that starts from NiMoO4 nanorods. The incorporation of Ni atoms in Mo–S could arouse the synergism of ternary Ni–Mo–S and create abundant defect sites, thus substantially improving the inherent catalytic activity and catalytic sites. More importantly, Ni endows Mo–S with excellent catalytic activity in alkaline solution. As a result, NiMoS3 exhibits large cathodic current, low overpotetnial, and stable durability for HER in H2SO4 and especially in KOH. The overpotetnial at current density of 10 mA cm–2 is as low as 126 mV in KOH, making it a promising candidate for HER electrocatalyst.

Electrostatic Self‐Assembly of the Composite La0.7Sr0.3MnO3@Ce0.75Zr0.25O2 as Electrocatalyst for the Oxygen Reduction Reaction in Aluminum–Air Batteries

AbstractLa1−xSrxMnO3 (LSM) has been proposed as one of the best oxygen reduction reaction catalysts (ORRCs) to substitute noble metals. It is well known that an improvement of the oxygen‐adsorption capacity is beneficial to the catalytic activity of LSM perovskites. Herein, the composite material La0.7Sr0.3MnO3@Ce0.75Zr0.25O2 (LSM@CZ) has been synthesized by a facile electrostatic self‐assembly method in a two‐step strategy. The CZ nanoparticles are well distributed on the surface of the LSM material. The LSM‐4CZ composite catalyst exhibits a good catalytic activity in alkaline solution. The onset potential, half‐wave potential, and electron transfer number of the LSM‐4CZ composite catalyst are 0.898 V, 0.695 V, and 4, respectively. The LSM‐4CZ composite catalyst has a good durability with current retention of 93.9 % after 80 000 s and it exhibits a much better stability than Pt/C, the retention of which is 83.5 %. If we used LSM‐CZ as the ORRC, the maximum power density of the Al–air battery reached 242.9 mW cm−2, which is approximately 40 % higher than that of the battery with LSM (177.3 mW cm−2). This indicates that the LSM@CZ composite material is a promising cathodic electrocatalyst for metal–air batteries.

Regulating Water-Reduction Kinetics in Cobalt Phosphide for Enhancing HER Catalytic Activity in Alkaline Solution.

Electrochemical water splitting to produce hydrogen renders a promising pathway for renewable energy storage. Considering limited electrocatalysts have good oxygen-evolution reaction (OER) catalytic activity in acid solution while numerous economical materials show excellent OER catalytic performance in alkaline solution, developing new strategies that enhance the alkaline hydrogen-evolution reaction (HER) catalytic activity of cost-effective catalysts is highly desirable for achieving highly efficient overall water splitting. Herein, it is demonstrated that synergistic regulation of water dissociation and optimization of hydrogen adsorption free energy on electrocatalysts can significantly promote alkaline HER catalysis. Using oxygen-incorporated Co2 P as an example, the synergistic effect brings about 15-fold enhancement of alkaline HER activity. Theory calculations confirm that the water dissociation free energy of Co2 P decreases significantly after oxygen incorporation, and the hydrogen adsorption free energy can also be optimized simultaneously. The finding suggests the powerful effectiveness of synergetic regulation of water dissociation and optimization of hydrogen adsorption free energy on electrocatalysts for alkaline HER catalysis.

Pt/Co Alloy Nanoparticles Prepared by Nanocapsule Method Exhibit a High Oxygen Reduction Reaction Activity in the Alkaline Media.

Oxygen reduction reaction (ORR) catalysts are one of the main topics for fuel cells and metal/air batteries. We found that the platinum–cobalt alloy nanoparticles prepared by our original nanocapsule method exhibited a high ORR catalytic activity in alkaline solution, compared with that of the existing alloy nanoparticles prepared by different methods. The effect of alloy composition on the ORR activity was investigated to find the optimum composition (approximately 40 atom %). We also found that the enhancement of the catalytic activity in alkaline solution appeared in a very narrow range of Co content compared with that in acidic solution.

High Surface Area NanoCOT Catalysts on Ni Foam Framework for Efficient Water Electrolysis

Carbon doped nanostructured TiO2 electrodes (NanoCOT) are prepared by anodizing titanium in a fluoride-based electrolyte followed by thermal annealing in an atmosphere of methane and hydrogen in the presence of Fe precursors. NanoCOT are highly conductive and contain more than 1 × 10^9 /cm2 of nanowires or nanotubes to enhance their double layer charge capacitance and electrochemical stability. This electrode material also exhibits enhanced oxygen evolution reaction (OER) catalytic activity in alkaline solution, providing a current density of 1.33 mA/cm2 at an overpotential of 0.42 V. This OER current density of a NanoCOT electrode is about 4 times higher than an oxidized Ir electrode and 15 times higher than a Pt electrode because of its nanostructured high surface area and favorable OER kinetics. The enhanced catalytic activity of NanoCOT is attributed to the presence of a continuous energy band of the titanium oxide electrode with predominantly reduced defect states of Ti (e.g., Ti^1+, Ti^2+, and Ti^3+) formed by chemical reduction with hydrogen and carbon. The OER performance of NanoCOT can also be further enhanced by decreasing its overpotential by 150 mV at a current density of 1.0 mA/cm2after coating its surface electrophoretically with 2.0 nm IrOx nanoparticles. Further improve can be obtained by using porous substrate such as Ni and Ti foam.

Facile electrodeposition of cauliflower-like S-doped nickel microsphere films as highly active catalysts for electrochemical hydrogen evolution

Self-supported cauliflower-like S-doped Ni microspheres grown on a Cu wire (NiSx/CW) are fabricated via a facile, one-step electrodeposition approach in ethaline, which exhibit highly active and durable HER catalytic activity in alkaline solution.

Investigation of the durability of a poly-p-phenylenediamine/carbon black composite for the oxygen reduction reaction

Nitrogen-doped carbon materials exhibiting high oxygen reduction reaction activity were prepared via the pyrolysis of a poly-p-phenylenediamine/carbon black composite. The as-synthesized catalyst showed excellent catalytic activity in alkaline solution, and outperformed commercial Pt/C in KOH solution (0.1 mol/L), as demonstrated by the higher current density and the more positive half-wave potential. Scanning electron microscopy and N2 adsorption-desorption analyses indicated that a composite structure, in which the N-rich surface of the poly-p-phenylenediamine had an increased active center concentration and the high external surface area of the carbon black was conducive to the mass transport, is highly beneficial in terms of promoting the oxygen reduction reaction. However, the activity of this catalyst underwent an obvious decrease following exposure to air for 30 d. X-ray photoelectron spectroscopy showed that the oxygen content in the catalyst was increased by prolonged air exposure. O 1s spectrum showed increases in the C=O and C–O components, suggesting that atmospheric oxygen reacted with the catalyst. This oxidation leaded to the deactivation of active center, thus the catalytic activity decreased. Based on these results, the stability in air of nitrogen-doped carbon materials must be taken into consideration when assessing applications as alternatives to platinum-based materials.

Overpotential-Induced Introduction of Oxygen Vacancy in La0.67Sr0.33MnO3 Surface and Its Impact on Oxygen Reduction Reaction Catalytic Activity in Alkaline Solution

Oxygen reduction reaction (ORR) catalytic activity of La0.67Sr0.33MnO3 epitaxial thin films was investigated in a KOH solution by using a rotating-disk electrode. We found that while the films exhibit ORR current, the current is not limited by oxygen transport resulting from the film electrode rotation and shows the large hysteresis against the potential sweep direction. This behavior is in stark contrast to the oxygen reduction reaction activity of an electrode ink made from LSMO bulk powder, whose ORR current is oxygen-transport limited. In situ synchrotron X-ray absorption spectroscopy also reveals that the valence state of Mn in the LSMO film surface is lowered under the reducing atmosphere caused by the overpotential. This indicates the overpotential-induced introduction of oxygen vacancies in the film surface. We also show that the ORR current of the LSMO films exposed to the reducing atmosphere is lowered than that of the original surface. These results indicate that the ORR catalytic activity of L...

NanoCOT: Low-Cost Nanostructured Electrode Containing Carbon, Oxygen, and Titanium for Efficient Oxygen Evolution Reaction.

Developing high-efficiency, durable, and low-cost catalysts based on earth-abundant elements for the oxygen evolution reaction (OER) is essential for renewable energy conversion and energy storage devices. In this study, we report a highly active nanostructured electrode, NanoCOT, which contains carbon, oxygen, and titanium, for efficient OER in alkaline solution. The NanoCOT electrode is synthesized from carbon transformation of TiO2 in an atmosphere of methane, hydrogen, and nitrogen at a high temperature. The NanoCOT exhibits enhanced OER catalytic activity in alkaline solution, providing a current density of 1.33 mA/cm(2) at an overpotential of 0.42 V. This OER current density of a NanoCOT electrode is about 4 times higher than an oxidized Ir electrode and 15 times higher than a Pt electrode because of its nanostructured high surface area and favorable OER kinetics. The enhanced catalytic activity of NanoCOT is attributed to the presence of a continuous energy band of the titanium oxide electrode with predominantly reduced defect states of Ti (e.g., Ti(1+), Ti(2+), and Ti(3+)) formed by chemical reduction with hydrogen and carbon. The OER performance of NanoCOT can also be further enhanced by decreasing its overpotential by 150 mV at a current density of 1.0 mA/cm(2) after coating its surface electrophoretically with 2.0 nm IrOx nanoparticles.

Oxygen Evolution Reaction on Zirconium Oxide Film in Alkaline Medium

Introduction Alkaline water electrolysis (AWE) is one of the hydrogen production methods without any carbon dioxide emission with renewable electric power supply. The AWE has several advantages compared with polymer electrolyte water electrolysis such as utilize of inexpensive materials [1]. However, in the case of connection of the AWE to electric fluctuant power from renewable energy, the degradation of the electrodes is accelerated [2]. For the practical use for AWE with renewable energies, a durable alternative material should be required. We focused on zirconium compounds as the alternative material because of their high activity for oxygen reduction reaction and high chemical stability [3]. In this study, the relationship between the catalytic activity for oxygen evolution reaction (OER) and preparing method of the zirconia film has been investigated as a fundamental study of the OER activity in alkaline solution. Experimental A zirconium plate (Zr purity: 99.2%) was used as a starting material, and oxidized for 10 minutes in the range of temperature from 400 to 700oC in air to prepare ZrO­2 / Zr electrode (ZrO2 / Zr_Temp. of oxidation). To prepare ZrO2 / Ti electrode, a Zr target was used in deposition method of an arc plasma gun (APD). ZrO2 was deposited on Ti rods for 6000 shots applied 100 V with a 360 μF capacitor at room temperature (ZrO2/ Ti_APD). After evacuation of the chamber, oxygen was introduced with 1 mL / min during deposition. Oxygen partial pressure in the chamber was 0.083 Pa. The frequency of the pulse was 3 Hz. The ZrO2 electrode, a reversible hydrogen electrode (RHE), and a glassy carbon plate were used as a working, reference, and counter electrodes. All measurements were performed under N2 atmosphere in 0.1 M KOH at 30oC. Cyclic voltammetry (CV) was conducted for 100 cycles between 0 and 1.0 V vs. RHE with the scan rate of 100 mV s-1 as a pretreatment. The OER activity of the ZrO2 electrodes was evaluated by slow scan voltammetry (SSV) between 1.0 and 2.0 V vs. RHE with 5 mV s-1 of the scan rate. The onset potential (E onset) defined by the potential at (geometric current density) in Tafel region was used as the index for OER activity. Results and discussion Figure 1 shows the polarization curves of the ZrO2 / Zr and ZrO2 / Ti electrodes. The ZrO2 / Zr_550oC had the highest geometric current density (i­ geo) in this study. The ZrO2 / Ti_APD had smaller current density than the ZrO2 / Zr_550 and 600oC. Figure 2 shows the Tafel plot of the ZrO2 / Zr_550oC and the ZrO2 / Ti_APD. The Tafel slope of OER on the ZrO2 / Zr_550oC was 70 mV dec-1, and it was smaller than that of the ZrO2 / Ti_APD of 108 mV dec-1. However, Tafel region of the ZrO2 / Ti_APD was at almost same potential as that of the ZrO2 / Zr_550oC. The i geo of ZrO2 / Ti_APD was crossed that of the ZrO2 / Zr_550oC at about 1.7 V. This might be affected by contact resistance between ZrO2films and Ti substrates or oxide film resistance. Figure 3 shows the E onset of OER on the ZrO2 electrodes as a function of the oxidation temperature. The E onset decreased with the increase of oxidation temperature in the range from 400oC to 550oC. Above 550oC, the E onset was almost constant. Thus, the active site of OER on the ZrO2 / Zr would be formed above 550oC. The E onset of OER on the ZrO2 / Ti_APD was the smallest potential of 1.59 V vs. RHE in the ZrO2electrodes in this study. Though the ZrO2 / Ti had the lower i geo than the ZrO2 / Zr electrode in higher i geo region, the E onset of OER on the ZrO2 / Ti_APD was the lowest in this study. Therefore, the ZrO2/ Ti_APD has potential for the high OER catalytic activity in alkaline solution and would have higher current density by improvement conductivity. Reference [1]. S. Mitsushima and K. Matsuzawa, J. Hydr . E ner . Sys . Soc. Jpn., 36, 11 (2011) (in Japanese). [2]. H. Ichikawa, K. Matsuzawa, Y. Kohno, I. Nagashima, Y. Sunada, Y. Nishiki, A. Manabe, and S. Mitsushima, ECS Trans., 58(33), 9 (2014). [3]. A. Ishihara, Y. Ohgi, K. Matsuzawa, S. Mitsushima, and K. Ota, Electrochim . Acta, 55, 8005 (2010). Figure 1

Bioinspired synthesis of nitrogen/sulfur co-doped graphene as an efficient electrocatalyst for oxygen reduction reaction

Efficient electrocatalyst of oxygen reduction reaction (ORR) is crucial for a variety of renewable energy applications and heteroatom-doped carbon materials have demonstrated promising catalytic performance towards ORR. In this paper we report a bioinspired method to synthesize nitrogen/sulfur (N/S) co-doped graphene as an efficient ORR electrocatalyst via self-polymerization of polydopamine (PDA) thin layer on graphene oxide sheets, followed by reacting with cysteine and finally thermal annealing in Argon (Ar) atmosphere. As-prepared N/S co-doped graphene exhibits significantly enhanced ORR catalytic activity in alkaline solution compared with pristine graphene or N-doped graphene. It also displays long-term operation stability and strong tolerance to methanol poison effect, indicating it a promising ORR electrocatalyst.