Bifunctional Catalytic Material Research Articles

Phosphorylated Co(OH)2@NiFe-LDH core–shell heterostructure for highly efficient alkaline water splitting

The development of transition metal bifunctional electrocatalysts with high activity, stability and cost-effectiveness is necessary for the overall water decomposition. In this work, a phosphorylated core–shell heterostructure bifunctional catalytic material with a nickel foam carrier, a Co(OH)2 nanowire array core and an ultrathin NiFe layered double hydroxide (NiFe-LDH) shell is synthesized. The solid contact between the NiFe-LDH shell and the highly conductive Co(OH)2 core brings about excellent electrical connectivity and an integrated hierarchical nanostructure that greatly improves the active specific surface area. Meanwhile, the phosphorylated hierarchical core–shell nanostructure enables the presence of a large amount of amorphous material at the edges, which leads to excellent activity and stability for oxygen evolution reactions (OER) and hydrogen evolution reactions (HER).

Construction of a novel high electrochemical performance nanosheet Co3O4@Fe2O3 bifunctional catalytic material for lithium-oxygen batteries

Lithium-oxygen battery (LOB) has attracted wide attention owing to its high specific energy and environmental protection advantages. However, LOB also has many problems, such as the discharge products accumulated around the pore size to block the oxygen diffusion channel. In this work, a Co3O4@Fe2O3 nanosheet composite catalytic material is designed, which can effectively improve the electron transfer in the catalytic process. Furthermore, due to the electronic interaction between Co3O4 and Fe2O3 in the heterostructure region, the optimal active sites for the adsorption and activation of the reactant molecules can be obtained so as to produce better ORR/OER bifunctional catalytic activity. Besides that, the interface between Co3O4 and Fe2O3 can stimulate more electrons to participate in the redox reaction and promote the reversible formation and decomposition of Li2O2. When Co3O4@Fe2O3 nanosheet composite as cathode catalyst, LOB can achieve a high discharge specific capacity of 5585 mAh/g with 141 stable charge and discharge cycles.

High-efficiency refractory organic pollutants removal boosted by combining heterogeneous electro-Fenton with electrochemical anodic oxidation over a broad pH range

Electrochemical anodic oxidation (AO) is a green and efficient treatment process for refractory pollutants degradation. The cathode in AO process generally serves as the counter electrode, and does not contribute significantly for pollutants removal. The heterogeneous electro-Fenton (EF) process uses the bifunctional catalytic material as cathode to produce H2O2 via 2e- oxygen reduction reaction and activate H2O2 decomposition to generate •OH for degrading pollutants. Herein, we investigated an integrated electrocatalytic process between heterogeneous EF and AO (EF+AO) to enhance refractory pollutants removal over a broad pH range without the production of iron-containing sludge. Total organic carbon removal of phenol by EF+AO was 98.2 % in 180 min under pH ∼5.9 and the applied current density of 1.0 mA cm−2, obviously higher than that of only EF (48.8 %) or AO (56.9 %). Significantly, EF+AO process can efficiently treat the actual coking wastewater that the chemical oxygen demand (COD) value gradually decreased from 312.3 mg L−1 to 47.8 mg L−1 with the low specific energy consumption of 14.0 – 25.7 kWh·(kg COD)−1. This process delivered excellent long-term durability in flow mode, retaining efficient degradation performance for phenol during 100 h of consecutive runs. Our results provide new insights into developing an energy-efficient electrocatalytic process for pollutants removal.

Bifunctional acid-activated montmorillonite catalyzed biodiesel production from non-food oil: Characterization, optimization, kinetic and thermodynamic studies

Utilizing robust heterogeneous catalysts to efficiently produce biodiesel from low-cost non-food oil is very important for replacing fossil energy to meet globally increasing energy demands and accelerate realization of carbon neutrality. In this study, a novel Lewis (L)-Brønsted (B) bifunctional catalytic material 30%Sn-MMT-SO3H was conveniently fabricated by ion-exchange and sulfonation using widely-sourced and biocompatible montmorillonite (MMT) as a matrix, which was successfully applied in direct conversion of Jatropha curcas oil (JCO) into biodiesel. Systematical characterization techniques showed that 30%Sn-MMT-SO3H presented a layered nanostructure along with a high specific surface area (145.32 m2/g), rich mesopores (5.8 nm), strong acidic intensity (1.801 mmol g−1), abundant accessible active sites, and outstanding chemical and thermal stability. Additionally, the single-factor method and response surface methodology (RSM) were employed to investigate optimal reaction conditions. Accordingly, the maximum biodiesel yield (93.1%) was achieved under conditions of 7 wt% catalyst dosage, 20.2 methanol/oil molar ratio at 150 °C for 7.5 h, and no significant decrease was observed after five cycles. Importantly, kinetic and thermodynamic behaviors together with possible reaction mechanisms were also determined. Compared with other reported catalysts, 30%Sn-MMT-SO3H exhibited satisfactory activity and reusability, showing promising prospects in industrialization of biodiesel mediated by heterogeneous acid catalysts.

Hierarchical VSe2-doped NiCoSex yolk-shelled porous prisms as enhanced bifunctional catalytic materials for highly efficient photovoltaics and hydrogen evolution

Herein, a facile assembly strategy and ion exchange reaction coupled with the following selenization treatment have been developed for the synthesis of V-doped transition metal nickel-cobalt selenide prism with hierarchical yolk-shelled structure (named as VSe2-NiCoSex), which have the outer shell of Ni–Co–VSe2 with the Ni–CoSe2 inner core. Notably, VSe2-NiCoSex presented prominent bifunctional electrocatalytic performances and excellent conductivity toward both dye-sensitized solar cells (DSSCs) and hydrogen evolution reactions (HERs) for water electrolysis. As for DSSCs, VSe2-NiCoSex electrode exhibited a remarkable power conversion efficiency (PCE) of 9.50%, Rct of 1.09 Ω and Epp of 231 mV than that of Pt (8.29%, 4.25 Ω and 414 mV) under the same testing conditions. Besides, VSe2-NiCoSex as HER catalyst delivers a lower overpotential of 84.3 mV at the current density of 10 mA cm−2 and a small Tafel slope of 49.1 mV dec−1 in 0.5 M H2SO4.

Curved Porous PdCu Metallene as a High-Efficiency Bifunctional Electrocatalyst for Oxygen Reduction and Formic Acid Oxidation.

Designing high-efficiency and newly developed Pd-based bifunctional catalytic materials still faces tremendous challenges for oxygen reduction reaction (ORR) and formic acid oxidation reaction (FAO). Metallene materials with unique structural features are considered strong candidates for enhancing the catalytic performance. In this work, we synthesized copper-doped two-dimensional curved porous Pd metallene nanomaterials via a simplistic one-pot solvothermal method. The updated catalysts served as sturdy bifunctional electrocatalysts for cathodal ORR and anodic FAO. In particular, the developed PdCu metallene exhibits excellent half-wave potential (0.943 V vs RHE) and mass activity (MA) (1.227 A mgPt-1) in alkaline solutions, which are 1.09 and 6.26 times higher than those of commercial Pt/C, respectively, indicating that the nanomaterials have abundant active sites, displaying surpassing catalytic performance for oxygen reduction. Furthermore, in an acidic formic acid electrolyte, PdCu metallene exhibits prominent MA with a value of 0.905 A mgPd-1, which is 2.76 times that of commercial Pd/C. The remarkable bifunctional catalytic performance of metallene materials can be attributed to the special structure and electronic effects. This work shows that metallene materials with curved and porous properties provide a scientific idea for the development and design of efficient and steady electrocatalysts.

Non-precious metal-based integrated electrodes for overall alkaline water splitting

A bifunctional electrocatalyst interface requires a superior charge transfer and good electric conductivity to produce an efficient and stable water splitting reaction. In the context of controlling the electrochemical activity of bifunctional catalytic materials, we demonstrate a novel approach to bridge conductive C-Qd-Mn interfaces with precise control. The excellent performance for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) can be dominantly attributed to the unique structure of C-Qds-Mn, which provides abundant active sites and facilitates electron transfer between electrode and electrolyte. Eco-friendly C-Qds were synthesized using a large-scale thermal assisted technique and utilized as electrocatalysts with Mn3O4 in alkaline splitting ToF (Turn over Frequency) calculation to make an effective combination. Due to their increased ECSA, conductivity, and electron-hole transfer, the prepared C-Qds-Mn delivered excellent HER/OER (0.494 V/1.6671V) activity, lower Standard deviation 0.006 V and 0.009V, surpassing the 10 mA limit comparable to commercially.

One Step Dimethyl Ether (DME) Synthesis from CO2 Hydrogenation over Hybrid Catalysts Containing Cu/ZnO/Al2O3 and Nano-Sized Hollow ZSM-5 Zeolites

The study has focused on the development of bifunctional catalytic materials for the direct DME synthesis from CO2/H2. The industrial Cu/ZnO/Al2O3 is used as the copper based catalyst for the first step of the methanol synthesis from CO2/H2. It will be combined with hollow nano-ZSM-5 zeolites with mesoporous shell as the acid catalyst of the second step the methanol dehydration to DME. The bifunctional materials will be tested in the direct DME synthesis from CO2/H2 under the following conditions: T = 225 °C, p = 30 bar, H2/CO2 = 3. Under our reaction conditions, CO was not observed, only the DME majority product (77.5%) and CH3OH (22.5%) were obtained.

Bifunctional Silicotungstic Acid and Tungstophosphoric Acid Impregnated Cu–Zn–Al & Cu–Zn–Zr Catalysts for Dimethyl Ether Synthesis from Syngas

In the present study, a set of methanol synthesis catalysts with different Cu/Zn/Al or Cu/Zn/Zr molar ratios were synthesized by a co-precipitation method. Silicotungstic acid and tungstophosphoric acid were impregnated into these materials to synthesize new bifunctional catalytic materials to be used in direct synthesis of dimethyl ether (DME) from syngas. In the case of methanol production, synthesized Cu/Zn/Al catalysts exhibited quite high methanol selectivity, reaching to approximately 87%. These results indicated that the dispersion of copper particles profoundly affected the selectivity of methanol. Direct synthesis of DME was investigated in the presence of heteropoly acid impregnated copper-based novel hybrid type bifunctional catalysts. Results revealed that product distributions were strongly influenced by the reaction temperature, pressure, heteropoly acid content, and type. Results proved that silicotungstic acid (STA) impregnated bifunctional catalysts showed much better catalytic performance than the tungstophosphoric acid (TPA) impregnated ones in DME synthesis from syngas. Very high dimethyl ether selectivity values were achieved in direct synthesis of dimethyl ether over the 25%, and 30% STA impregnated methanol synthesis catalysts, at 275 °C and 50 bar. DME selectivity presented an increasing trend due to the increase in heteropoly acid content over methanol synthesis catalysts. The silicotungstic acid incorporated (30%) Cu/Zn/Al catalyst, having a composition of 6/3/1 (30STA@CZA:631), showed the highest CO conversion and DME selectivity. However, coke formation over this catalyst was much more than the catalyst containing 25% STA. This is mainly due to the higher Bronsted acidity of 30STA@CZA:631 than 25STA@CZA:631. Low coke formation, together with quite high DME selectivity values achieved with 25STA@CZA:631, is a worthy distinction of this catalyst for the direct synthesis of DME from synthesis gas. Novel hybrid type catalysts are successfully synthesized for direct synthesis of dimethyl ether process. Heteropoly acid incorporated methanol synthesis catalysts are very active and stable in the direct synthesis of dimethyl ether process. Silicotungstic acid (STA) impregnated copper-based catalyst exhibits a superior performance than the tungstophosphoric acid impregnated catalyst.

Insert Zn2+ in Tetrahedral Sites of Bi-metal Zn-Co Spinel Oxides with High Oxygen Catalytic Performance for Liquid and Flexible Zinc-Air Batteries

Nowadays, it is very challenging to develop a low-cost, highly active and stable bi-functional catalyst for accelerating oxygen reduction reaction (ORR) and oxygen evolution (OER) reaction during the charge and discharge process of zinc-air battery. Herein, we successfully design a novel bi-metal oxide hybrid catalyst (ZnCo2O4-CNT) by inserting Zn ions. Benefiting from the robust synergetic effects between porous ZnCo2O4 and CNTs, the high conductivity and the unique nanostructure, the ZnCo2O4-CNT shows lots of accessible active sites and improved reactants and electrons transfer. As expected, the hybrid shows higher ORR and OER performances with larger limited diffusion current density (5.72 mA cm−2) and lower OER over-potential (0.49 V) than Pt/C and other ZnCo2O4-CNT samples. In addition, rechargeable zinc-air battery assembled with the bi-functional catalyst exhibits a high power density of 249.4 mW cm−2, a strong discharge durability and charge-discharge stability of 240 cycles. Notably, the flexible zinc-air battery also shows good battery performances with high power density and good flexibility. Hence, exploiting efficient bi-functional catalytic materials with excellent ORR and OER performance and assembling flexible devices will improve the development of current zinc-air batteries battery industry.

Tuning the Bifunctional Oxygen Electrocatalytic Properties of Core-Shell Co3O4@NiFe LDH Catalysts for Zn-Air Batteries: Effects of Interfacial Cation Valences.

The rational design of excellent electrocatalysts is significant for triggering the slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable metal-air batteries. Hereby, we report a bifunctional catalytic material with core-shell structure constructed by Co3O4 nanowire arrays as cores and ultrathin NiFe-layered double hydroxides (NiFe LDHs) as shells (Co3O4@NiFe LDHs). The introduction of Co3O4 nanowires could provide abundant active sites for NiFe LDH nanosheets. Most importantly, the deposition of NiFe LDHs on the surface of Co3O4 can modulate the surface chemical valences of Co, Ni, and Fe species via changing the electron donor and/or electron absorption effects, finally achieving the balance and optimization of ORR and OER properties. By this core-shell design, the maximum ORR current densities of Co3O4@NiFe LDHs increase to 3-7 mA cm-2, almost an order of magnitude increases compared to pure NiFe LDH (0.45 mA cm-2). Significantly, an OER overpotential as low as 226 mV (35 mA cm-2) is achieved in the designed core-shell catalyst, which is comparable to and/or even better than those of commercial Ir/C. Hence, the primary zinc-air battery employing Co3O4@NiFe LDH as an air electrode achieves a high specific capacity (667.5 mA h g-1) and first-class energy density (797.6 W h kg-1); the rechargeable battery can show superior reversibility, excellent stability, and voltage gaps of ∼0.8 V (∼60% of round-trip efficiency) in >1200 continuous cycles. Furthermore, the flexible quasi-solid-state zinc-air battery with bendable ability holds practical potential in portable and wearable electronic devices.

Efficient Catalytic Production of Biodiesel with Acid-Base Bifunctional Rod-Like Ca-B Oxides by the Sol-Gel Approach

The search for acid-base bifunctional catalysts has become a hot topic in the preparation of biofuels from renewable resources. In the present work, a series of novel acid-base bifunctional metal-boron catalysts were successfully prepared by a sol-gel method and characterized by XRD, IR, SEM, TEM, TGA, BET, and TPD. Among those bifunctional solid materials, the Ca-B(700) catalyst had the highest density of both acid and base sites and showed excellent catalytic performance in the production of biodiesel from nonedible oils with high acid value. Under the optimal reaction conditions of 20/1 methanol/oil mole ratio and 4 wt % catalyst dosage at 105 °C for 2 h, a high biodiesel yield of 96.0% could be obtained from Jatropha curcas oil in one-pot. In addition, Ca-B(700) was also applicable to producing biodiesel from Firmiana platanifolia L.f. oil in a relatively low acid value, with an almost quantitative yield (98.5%) at 65 °C after 2 h. The Ca-B(700) catalyst had good stability and reusability, which is a promising acid-base bifunctional catalytic material for the preparation of biodiesel.

Rational construction of novel rose petals-like yttrium molybdate nanosheets: A Janus catalyst for the detection and degradation of cardioselective β-blocker agent acebutolol

Metal molybdates has paid emerging attention in variety of energy and environmental applications owing to their extra-ordinary physicochemical properties. In this regard, novel rose petal-like yttrium molybdate nanosheets (YMoO4; YM NSs) was successfully designed through a simple wet chemical method and fabricated as advanced bifunctional catalytic material. The as-prepared YM NSs catalyst were systematically scrutinized in terms of their crystal structure, morphologies, and optical properties using XRD, Raman, FE-SEM, HR-TEM, XPS and UV-DRS analysis. The bifunctional electro- and photocatalytic activity of as-prepared YM NSs was investigated towards the detection and degradation of β-adrenergic receptor-blocker agent acebutolol (ACB) for the first time. Interestingly, the YM NSs modified glassy carbon electrode (YM NSs/GCE) demonstrates an excellent electrocatalytic activity towards ACB with wider linear response ranges (0.01–9.6 µM, 13–1632 µM), lower detection limit (2.5 nM), good sensitivity (2.21 µA µM−1cm−2) and excellent selectivity even in the existence of some common cations, anions and biological substances. The sensor (YM NSs/GCE) was successfully applied to determine the level of ACB in tablet, urine and water samples. Furthermore, the YM NSs was performed as superior photocatalyst for the degradation of as detected ACB. The YM NSs could degrade above 99% and mineralize above 74% of ACB aqueous suspension under visible light irradiation with superior recycling stability.

A novel Mn3O4/MnO nano spherical transition metal compound prepared by vacuum direct current arc method as bi-functional catalyst for lithium-oxygen battery with excellent electrochemical performances

In this paper, a novel Mn3O4/MnO nano spherical transition metal compound as bi-functional catalyst for air electrode of lithium-oxygen battery is prepared by vacuum direct current arc method. Through physical property characterization, it shows that the Mn3O4/MnO particle size can be controlled between 40 and 60 nm and evenly distributed inside the carbon material. In addition, photoluminescence test result indicates that this material has better electronic conductivity and catalytic activity than traditional MnO2 catalyst owing to some defects in the crystal structure. The cyclic voltammetry results display that the oxidation and reduction reactions are both very obvious even at high scanning rate, although only one kind of catalyst is employed in the air electrode. This proves that the Mn3O4/MnO nano spherical transition metal compound can be as a bi-functional catalytic material. Electrochemical impedance spectroscopy also displays that the charge transfer resistance of Mn3O4/MnO catalyst is smaller and the ion diffusion speed is faster. Through charge and discharge test, it can be concluded that the voltage platform of the lithium-oxygen battery with Mn3O4/MnO as bi-functional catalyst is flat and the discharge voltage can reach 2.7 V. The specific energy can reach 7102 Wh·kg−1 at 0.025 mA cm−2 current density and a capacity limit of 1000 mAh·g−1, it can carry out the 31 non capacity decay charge and discharge cycles.

Stainless Steel Scrubber: A Cost Efficient Catalytic Electrode for Full Water Splitting in Alkaline Medium

Sometimes, searching for a cost efficient bifunctional catalytic material for water splitting can be accomplished from a very unlikely place. In this work, we are reporting such a discovery of utilizing the stainless steel (SS) scrubber directly as a catalytic electrode for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) of water electrolysis in 1 M KOH. The iR corrected overpotential calculated at an areal current density of 10 mA cm–2 for a SS scrubber in HER is 315 mV which is 273 mV higher than Pt/C. Similarly, the SS scrubber required 418 mV at 10 mA cm–2 which is just 37 and 98 mV higher than Ni(OH)2 and RuO2. Interestingly, the kinetic analysis revealed that the SS scrubber had facile kinetics for both HER and OER in 1 M KOH as reflected by their corresponding Tafel slope values viz., 121 and 63 mV dec–1, respectively. In addition, the two electrode cell fabricated using the same SS scrubber electrode delivered 10 mA cm–2 at 1.98 V. Beyond everything, the SS scrubber had shown...

Metal Nanoparticles Supported on Perfluorinated Superacid Polymers: A Family of Bifunctional Catalysts for the Selective, One‐Pot Conversion of Vegetable Substrates in Water

AbstractWe describe the rational design of a new versatile family of bifunctional catalytic materials based on the combination of supported metal nanoparticles (Pd, Rh, Ru) and the superacid, perfluorinated Aquivion® PFSA polymer. The heterogeneous catalysts were tested in the multi‐step valorisation of representative plant derivatives to high‐added‐value chemicals. Particularly, the conversion of (+)‐citronellal to (‐)‐menthol and levulinic acid to γ‐valerolactone was achieved in one pot and in one stage in the water phase and shows full selectivity at a high conversion level under mild reaction conditions. The results are discussed in terms of the catalyst micro‐structure.

Electrocatalytic Properties of Vanadate Glass for Metal-Air Rechargeable Battery

A metal-air battery has a high energy density because they can use atmospheric oxygen as the electrode active material. It is expected that the battery could be used for the electric vehicle which demands power sources with a high energy-density. This rechargeable battery needs bifunctional catalytic materials, which involve effective oxygen reduction/evolution at the air electrode at the discharge/charge process. In this study, a new bifunctional catalytic material for the air electrode has been developed using a conductive vanadate glass. Conductivity of vanadate glass, 20BaO·10Fe2O3·70V2O5, was reported to be easily tunable over a wide range (10-7 - 10-1 S･cm-1) when the local distortion of the glass skeleton was removed by means of the annealing [1]. Utilizing these characteristics, new catalytic materials have been prepared by adding MnO2 and NiO for the oxygen reduction and evolution, respectively. 20BaO·5MnO2·5NiO·70V2O5 glass was synthesized by melting the mixture composed of BaCO3, MnO2, NiO, and V2O5 at 1100 °C for 2 hours. The vanadate glass was annealed at 450 °C for various times (0, 30, 60, and 300 min.). Pulverized vanadate glass was utilized for the preparation of the air electrode by mixing the powder with 7.5 mass% of poly (tetrafluoroethylene) (PTFE), which was hot-pressed on a gas diffusion layer over a Ni metal mesh. The electrode connected to a Cu wire was mounted onto the window of Teflon-made cell. 8M KOH aqueous solution and a Pt mesh were placed inside the Teflon cell as the electrolyte and the counter electrode, respectively. The temperature of the Teflon cell was held constant by soaking it into a water tank kept at 60 °C. Anodic and cathodic polarization measurements were carried out using a potentiostat. An Hg/HgO electrode was used as the reference electrode. The electrical conductivity of the as-prepared vanadate glass was 5.4 × 10 -6 S cm-1 at RT. After the annealing at 450 oC for 300 min, it increased to 1.1 × 10 -2 S cm-1. Figure shows the anodic and cathodic polarization curves of 20BaO·5MnO2·5NiO·70V2O5 glass electrodes. The vanadate electrode showed an excellent bifunctional oxygen reduction/evolution activity, being comparable to that of the materials reported in the literature, like polycrystalline LaNiO3 [2]. This vanadate glass could be a highly potential candidate for the bifunctional catalytic material for the rechargeable metal-air battery.

Efficient electrochemical water splitting catalyzed by electrodeposited NiFe nanosheets film

Cost-effective bifunctional oxygen- and hydrogen-evolving electrocatalysts made from earth-abundant elements are crucial for efficient water splitting. In this communication, we report a versatile and one-step electrodeposition of NiFe nanosheets film on Ni foam (NiFe/NF) as a bifunctional catalytic material with high activity and stability for overall water splitting in basic electrolytes. The two-electrode electrolyzer using NiFe/NF as both anode and cathode can afford current density of 10 mA cm−2 at a cell voltage of 1.64 V, which stimulates the design and development of transition metal alloy nanostructures as attractive bifunctional catalysts for electrochemical production of hydrogen fuels.

Bifunctional catalytic material: An ultrastable and high-performance surface defect CeO2 nanosheets for formaldehyde thermal oxidation and photocatalytic oxidation

Eu-doped CeO2 nanosheets were obtained on Ti substrate by facile anodic electrodeposition and annealing in N2 atmosphere. The composition of the Eu cations doped into the CeO2 nanosheets can be easily tuned by adjusting the ratio of Eu to Ce, which promoted the formation of surface defects. Compared to pristine CeO2 nanosheets, the as-prepared 4% Eu/CeO2 nanosheets exhibited a much lower complete temperature (120°C) of thermal oxidation for HCHO and a much longer stability as long as 100h. Significantly, the Eu-doped CeO2 nanosheets also show a much improved photocatalytic performance for removing HCHO under the visible light irradiation. The excellent performance of 4% Eu/CeO2 nanosheets could be attributed to the abundance of surface defects, high specific surface area and large pore volume, high redox ability, narrowed band gap and enhanced optical absorption, and excellent response in the visible region of solar spectrum. Therefore, this work provides a facile and cost-effective strategy for the design and fabrication of multifunctional catalyst toward HCHO removal.

Nonstoichiometric perovskite CaMnO(3-δ) for oxygen electrocatalysis with high activity.

Perovskite oxides offer efficient and cheap electrocatalysts for both oxygen reduction reactions and oxygen evolution reactions (ORR/OER) in diverse oxygen-based electrochemical technologies. In this study, we report a facile strategy to enhance the electrocatalytic activity of CaMnO3 by introducing oxygen defects. The nonstoichiometric CaMnO(3-δ) (0 < δ ≤ 0.5) was prepared through thermal reduction of pristine perovskite microspheres and nanoparticles, which were synthesized from thermal-decomposition of carbonate precursors and the Pechini route, respectively. The as-prepared samples were analyzed by chemical titration, structural refinement, thermogravimetric analysis, and energy spectrometry. In 0.1 M KOH aqueous solution, the nonstoichiometric CaMnO(3-δ) with δ near 0.25 and an average Mn valence close to 3.5 exhibited the highest ORR activity (36.7 A g(-1) at 0.70 V vs RHE, with onset potential of 0.96 V), which is comparable to that of benchmark Pt/C. Density functional theory (DFT) studies and electrical conductivity measurement revealed that the enhanced ORR kinetics is due to facilitated oxygen activation and improved electrical properties. Besides high activity, the nonstoichiometric perovskite oxides showed respectable catalytic stability. Furthermore, the moderate oxygen-defective CaMnO(3-δ) (δ ≈ 0.25) favored the OER because of the improved electrical conductivity. This study makes nonstoichiometric CaMnO(3-δ) a promising active, inexpensive bifunctional catalytic material for reversible ORR and OER.