NC Catalyst Research Articles

Metal - organic frameworks derived Ni5P4/NC@CoFeP/NC composites for highly efficient oxygen evolution reaction

As an efficient non-precious metal catalyst for the oxygen evolution reaction (OER), phosphides suffer from poor electrical conductivity, so it is still a challenge to reasonably design their structures to further improve their conductivity and OER performances. Here, we present a novel Ni5P4/N-doped carbon@CoFeP/N-doped carbon composite (Ni5P4/NC@CoFeP/NC) as electrocatalysts for OER. This elaborate structure consists of Ni5P4/NC derived from Ni-MOF and CoFeP/NC derived from CoFe-Prussian blue analog MOF (Co-Fe PBA). The cube-like CoFeP/NC are scattered and uniformly coated on the sheet of Ni5P4/NC flowers. Among them, NC can enhance the conductivity of phosphides, while CoFeP/NC can increase the electrochemical active area, which benefit the properties of Ni5P4/NC@CoFeP/NC. Notably, the Ni5P4/NC@CoFeP/NC catalyst possesses outstanding OER performances with a low overpotential of 260 and 303 mV at a current density of 10 and 100 mA·cm−2, an ultra-low Tafel slope of 31.1 mV·dec-1 and excellent stability in 1 M KOH. XPS analysis shows that proper chemical composition promotes the oxidation of transition metal species and the chemisorption of OH–, thus accelerating the OER kinetics. Therefore, this work provides a hopeful method for designing and preparing transition metal phosphide/carbon composite as OER electrocatalysts.

Atomically Dispersed Fe–Co Dual Metal Sites as Bifunctional Oxygen Electrocatalysts for Rechargeable and Flexible Zn–Air Batteries

Single-metal site catalysts have exhibited highly efficient electrocatalytic properties due to their unique coordination environments and adjustable local structures for reactant adsorption and electron transfer. They have been widely studied for many electrochemical reactions, including oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, it remains a significant challenge to realize high-efficiency bifunctional catalysis (ORR/OER) with single-metal-type active sites. Herein, we report atomically dispersed Fe–Co dual metal sites (FeCo–NC) derived from Fe and Co co-doped zeolitic imidazolate frameworks (ZIF-8s), aiming to build up multiple active sites for bifunctional ORR/OER catalysts. The atomically dispersed FeCo–NC catalyst shows excellent bifunctional catalytic activity in alkaline media for the ORR (E1/2 = 0.877 V) and the OER (Ej=10 = 1.579 V). Moreover, its outstanding stability during the ORR and the OER is comparable to noble-metal catalysts (Pt/C and RuO2). The atomic dispersion state, coordination structure, and the charge density difference of the dual metal site FeCo–NC were characterized and determined using advanced physical characterization and density functional theory (DFT) calculations. The FeCo–N6 moieties are likely the main active sites simultaneously for the ORR and the OER with improved performance relative to the traditional single Fe and Co site catalysts. We further incorporated the FeCo–NC catalyst into an air electrode for fabricating rechargeable and flexible Zn–air batteries, generating a superior power density (372 mW cm–2) and long-cycle (over 190 h) stability. This work would provide a method to design and synthesize atomically dispersed multi-metal site catalysts for advanced electrocatalysis.

Single Ni active sites with a nitrogen and phosphorus dual coordination for an efficient CO2 reduction.

Transition metal single-atom catalysts (SACs) have emerged as a research hotspot in CO2RRs. However, tuning the electronic configuration of a metal single-atom by employing new heteroatoms still remains a challenge. Herein, a carbon matrix loaded with a N and P co-coordinated Ni single-atom (denoted as Ni-NPC) was prepared for an efficient CO2RR. XANES and EXAFS were conducted to explore the coordination environment and charge distribution of the Ni-NPC catalyst. DFT calculations indicated that the Ni atom gained electrons from the P atom, and the Ni-NPC sample had a decreased energy barrier of +0.97 eV after doping with P atoms, which was favorable to overcome the limiting-step bottleneck for promoting CO2RR. Due to the rich Ni atomic active sites and superior P-doping effect, Ni-NPC exhibited a maximum FECO of 92% with a high current density of 22.6 mA cm-2 at -0.8V vs. RHE, which was far superior to those of NC, NPC and Ni-NC catalysts. Moreover, both the FECO and current density of the Ni-NPC catalyst remained stable for more than 16 h at -0.8 V vs. RHE, indicating a high stability for long-term CO2RR experiments.

One-Pot Production of 2,5-Furandimethanol from Fructose Co-catalyzed with Formic Acid and Heterogeneous Co Catalysts

2,5-Furandimethanol (FDM) is currently produced via a two-step process involving fructose dehydration over inorganic acids (H2SO4 and HCl) and the subsequent hydrogenation of 5-hydroxymethylfurfural (HMF) with H2. Because of the separation difficulty and unstable feature of HMF, the direct transformation of hexose to FDM is still challenging yet crucial. In this work, we first reported that formic acid served as both a renewable Bronsted acid and a hydrogen donor for one-pot dehydration–hydrogenation of fructose over a heterogeneous Co catalyst. Under optimal conditions of 170 °C for 3 h, 60.2% FDM yield was achieved with full conversion of fructose. Kinetic studies showed that the apparent activation energy (Ea) of the one-pot dehydration–hydrogenation of fructose was 80.5 kJ/mol and indicated that the rate-determining step of the whole process is fructose dehydration. The Co–NC catalyst was reusable and was also capable of gram-scale one-pot dehydration–hydrogenation of fructose.

Ag/LDH-itaconic acid-gellan gam nanocomposites: Facile and green synthesis, characterization, and excellent catalytic reduction of 4-nitrophenol

The catalytic reduction reaction is one of the most commonly used solutions to convert high-risk contaminants into safe or low-risk materials. Today, with the increasing water pollution, the urgent need for efficient and effective catalysts is felt more than ever. For this purpose, for the first time, a green catalyst composed of silver nanoparticles anchored on itaconic acid-modified Ca-Al layered double hydroxide/gellan gum nanocomposite (Ag/LDH-ITA-GG NC) was prepared from a green approach without the use of any toxic organic solvents. To gain an in-depth insight into the physicochemical properties of the catalyst, different techniques including nitrogen adsorption-desorption isotherms, FESEM/mapping, FTIR, TGA, and XRD were used. The catalytic performance of the Ag/LDH-ITA-GG NC toward 4-nitrophenol reduction by NaBH4 was investigated. The calculated values of the apparent rate constant for this reaction are 0.2142 min−1 (for 1.0 mg of the catalyst), 0.2375 min−1 (for 3.0 mg of the catalyst), and 0.2550 min−1 (for 5.0 mg of the catalyst), indicating that the catalytic conversion of 4-nitrophenol to 4-aminophenol on the Ag/LDH-ITA-GG NC catalyst follows the pseudo-first-order kinetics and is comparable to the previous findings in the literature. The results of this study indicated that Ag/LDH-ITA-GG NC can potentially be utilized as an auspicious high efficient green catalyst for the reduction of pollutants like 4-nitrophenol.

Unraveling the Origin of Sulfur-Doped Fe-N-C Single-Atom Catalyst for Enhanced Oxygen Reduction Activity: Effect of Iron Spin-State Tuning.

Heteroatom doped atomically dispersed Fe1 -NC catalysts have been found to show excellent activity toward oxygen reduction reaction (ORR). However, the origin of the enhanced activity is still controversial because the structure-function relationship governing the enhancement remains elusive. Herein, sulfur(S)-doped Fe1 -NC catalyst was obtained as a model, which displays a superior activity for ORR towards the traditional Fe-NC materials. 57 Fe Mössbauer spectroscopy and electron paramagnetic resonance spectroscopy revealed that incorporation of S in the second coordination sphere of Fe1 -NC can induce the transition of spin polarization configuration. Operando 57 Fe Mössbauer spectra definitively identified the low spin single-Fe3+ -atom of C-FeN4 -S moiety as the active site for ORR. Moreover, DFT calculations unveiled that lower spin state of the Fe center after the S doping promotes OH* desorption process. This work elucidates the underlying mechanisms towards S doping for enhancing ORR activity, and paves a way to investigate the function of broader heteroatom doped Fe1 -NC catalysts to offer a general guideline for spin-state-determined ORR.

Activating Inert Surface Pt Single Atoms via Subsurface Doping for Oxygen Reduction Reaction.

The performance of single-atom catalysts strongly depends on their particular coordination environments in the near-surface region. Herein, we discover that engineering extra Pt single atoms in the subsurface (Ptsubsurf) can significantly enhance the catalytic efficiency of surface Pt single atoms toward the oxygen reduction reaction (ORR). We experimentally and theoretically investigated the effects of the Ptsubsurf single atoms implanted in different positions of the subsurface of Co particles. The local environments and catalytic properties of surface Pt1 are highly tunable via Ptsubsurf doping. Specifically, the obtained Pt1@Co/NC catalyst displays a remarkable performance for ORR, achieving mass activity of 4.2 mA μgPt-1 (28 times higher than that of commercial Pt/C) at 0.9 V versus reversible hydrogen electrode (RHE) in 0.1 M HClO4 solution with high stability over 30000 cycles.

N-doped ZrO2 nanoparticles embedded in a N-doped carbon matrix as a highly active and durable electrocatalyst for oxygen reduction

Fabricating highly efficient and robust oxygen reduction reaction (ORR) electrocatalysts is challenging but desirable for practical Zn-air batteries. As an early transition-metal oxide, zirconium dioxide (ZrO2) has emerged as an interesting catalyst owing to its unique characteristics of high stability, anti-toxicity, good catalytic activity, and small oxygen adsorption enthalpies. However, its intrinsically poor electrical conductivity makes it difficult to serve as an ORR electrocatalyst. Herein, we report ultrafine N-doped ZrO2 nanoparticles embedded in an N-doped porous carbon matrix as an ORR electrocatalyst (N-ZrO2/NC). The N-ZrO2/NC catalyst displays excellent activity and long-term durability with a half-wave potential (E1/2) of 0.84 V and a selectivity for the four-electron reduction of oxygen in 0.1 M KOH. Upon employment in a Zn-air battery, N-ZrO2/NC presented an intriguing power density of 185.9 mW cm−2 and a high specific capacity of 797.9 mA h gZn−1, exceeding those of commercial Pt/C (122.1 mW cm−2 and 782.5 mA h gZn−1). This excellent performance is mainly attributed to the ultrafine ZrO2 nanoparticles, the conductive carbon substrate, and the modified electronic band structure of ZrO2 after N-doping. Density functional theory calculations demonstrated that N-doping can reduce the band-gap of ZrO2 from 3.96 eV to 3.33 eV through the hybridization of the p state of the N atom with the 2p state of the oxygen atom; this provides enhanced electrical conductivity and results in faster electron-transfer kinetics. This work provides a new approach for the design of other enhanced semiconductor and insulator materials.

High-pressure synthesis of CO and syngas from CO2 reduction using Ni−N-doped porous carbon electrocatalyst

Electrochemical conversion of CO2 to CO or syngas (CO/H2 mixture) is considered one of the most promising approaches to valorise waste-CO2. To develop the process on industrial scale, it would be necessary to use selective and inexpensive electrodes and to obtain high productivities with low energy consumption. In this frame, Ni−NC catalysts are considered among the most interesting ones because of their relatively low cost, high faradaic efficiency in CO (FECO), and high stability. However, up to now, quite low productivities were obtained as a result of low current densities achieved in aqueous electrolytes. In this work, we have evaluated the performances of a Ni−NC electrocatalyst at relatively high carbon dioxide pressures (5–30 bar) in a wide range of cell potentials and current densities. It is found that proper selection of CO2 pressure and catalyst loading improves drastically the performance of the process, obtaining high FECO (close to 100%), high current densities (>100 mA cm−2), and high productivities. Furthermore, it is shown that it is possible to obtain syngas with a target ratio of two between H2 and CO under various operating conditions. As an example, syngas was obtained with FE close to 100% and a productivity of ∼18 mol h−1 m−2 working at 30 bar with a current density close to 195 mA cm−2.

Microporous nitrogen-doped carbon from polyaniline as a highly efficient and stable catalyst for acetylene hydrochlorination

BackgroundAs a hot alternative to toxic industrial catalyst for acetylene hydrochlorination recently, N-doped carbon material (NC) catalysts have not yet exhibited both good activity and stability. MethodsHerein, NC catalysts with special physicochemical characteristics (abundant specific surface area and proper nitrogen content) were presented by the calcination of protonated polyaniline via chemical polymerization conditions. Significant FindingsA comparison of the performance between the novel catalysts and industrial 5% HgCl2/AC catalyst for acetylene hydrochlorination was evaluated under same acetylene gas hourly space velocity condition. The P-NC-1173-A6V12 catalyst exhibited a better initial acetylene conversion as well as stability at a high temperature reaction condition. The excellent catalytic stability is improved by the synergetic effect of abundant pore structure (especially micropores) and proper nitrogen species. In addition, carbon deposition is the main deactivation reason of catalyst. This work provides a facile method to prepare an environmentally friendly non-metallic catalyst with the potential for acetylene hydrochlorination.

CoOx @Co-NC Catalyst with Dual Active Centers for Enhanced Oxygen Evolution: Breaking Trade-Off of Particle Size and Metal Loading.

Increasing the metal loading and downsizing the metal particle size are two effective ways to boost the electrochemical performance of catalysts. However, it is difficult to simultaneously increase the metal loading and reduce the particle size since isolated individual atoms are easy to aggregate into nanoparticles when increasing the metal loading. To tackle this contradiction, we report a bottom-up ligand-mediated strategy to facilely prepare ultrafine CoOx nanoclusters anchored on a Co-N-containing carbon matrix (CoOx @Co-NC). The co-exist of N and O atoms prevent Co atoms agglomerating into large particles and allowing the formation of ultrafine dispersed Co species with large Co loading (up to 20 wt.%). Since the relationship between ultrasmall size and large metal loading is well balanced, the CoOx nanoclusters have no inhibitory effect, but facilitate the catalytic performance of Co-N4 sites during OER process. Consequently, due to the synergistic effect of ultrafine CoOx nanoclusters and Co-N4 macrocycles, the as-synthesized CoOx @Co-NC exhibit promising OER activity (η10 =370 mV, Tafel plot=40 mV/dec), bettering than that of benchmark RuO2 (η10 =411 mV, Tafel plot=72 mV/dec). This ligand-mediated strategy to synthesize carbonaceous materials containing dual active centers with large metal loading is promising for developing active and stable catalysts for electrocatalytic applications.

Engineering iron single atomic sites with adjacent ZrO2 nanoclusters via ligand–assisted strategy for effective oxygen reduction reaction and high–performance Zn–air batteries

• SA Fe@ZrO 2 /NC is synthesized by ligand–assisted strategy with single Fe atoms and adjacent ZrO 2 . • The SA Fe@ZrO 2 /NC exhibits much better catalytic performance toward ORR. • A Zn-air battery based on SA Fe@ZrO 2 /NC shows excellent performance. • DFT reveals the role of ZrO 2 in modulating electron structure of single Fe atoms and ORR activity. Atomically dispersed iron–nitrogen–carbon (Fe–N–C) catalyst is a promising candidate to replace Pt for oxygen reduction reaction (ORR). To enhance ORR activity of Fe–N–C catalysts, the density and distribution of isolated Fe–N 4 sites should be further optimized. Herein, a ligand–assisted strategy to synthesis of single atomic Fe–N–C derived from Zr–metal–organic frameworks (Zr–MOFs) is proposed. During preparation, –NO 2 (from 2–nitroterephthalic acid ligands) in Zr–MOFs not only acts as the anchoring sites to capture Fe–polydopamine (FePDA) source but also plays a crucial role in modulating the Fe − N 4 configuration. The resulting SA Fe@ZrO 2 /NC catalyst consists of FeN 4 sites with adjacent ZrO 2 in N–doped carbon, in which in–situ introduction of ZrO 2 positively enhance O 2 adsorption ability. Due to the moderate pore structure, atomically dispersed Fe–N 4 active sites, and the strong interface interaction between isolated Fe atoms and ZrO 2 nanocluster, the as–prepared catalyst exhibits comparable ORR activity and outstanding stability in alkaline solution. When assembled in a rechargeable Zn–air battery, the battery with SA Fe@ZrO 2 /NC air electrode delivers a stable open circuit voltage, high–power density (250 mW cm −2 ) and discharge specific capacity (730 mA h g Zn −1 ). It also demonstrates a long cycle life and good rate performance. Density functional theory calculation results reveals that the adjacent ZrO 2 nanocluster modulates the electron structure of Fe atoms in FeN 4 sites with an improved ORR process and activity. This work provides a facile strategy for preparing efficient single atomic Fe–N–C catalyst to drive the oxygen reduction reaction in Zn–air batteries.

Surface site density and utilization of platinum group metal (PGM)-free Fe-NC and FeNi-NC electrocatalysts for the oxygen reduction reaction.

Pyrolyzed iron-based platinum group metal (PGM)-free nitrogen-doped single site carbon catalysts (Fe–NC) are possible alternatives to platinum-based carbon catalysts for the oxygen reduction reaction (ORR). Bimetallic PGM-free M1M2–NC catalysts and their active sites, however, have been poorly studied to date. The present study explores the active accessible sites of mono- and bimetallic Fe–NC and FeNi–NC catalysts. Combining CO cryo chemisorption, X-ray absorption and 57Fe Mössbauer spectroscopy, we evaluate the number and chemical state of metal sites at the surface of the catalysts along with an estimate of their dispersion and utilization. Fe L3,2-edge X-ray adsorption spectra, Mössbauer spectra and CO desorption all suggested an essentially identical nature of Fe sites in both monometallic Fe–NC and bimetallic FeNi–NC; however, Ni blocks the formation of active sites during the pyrolysis and thus causes a sharp reduction in the accessible metal site density, while with only a minor direct participation as a catalytic site in the final catalyst. We also use the site density utilization factor, ϕSDsurface/bulk, as a measure of the metal site dispersion in PGM-free ORR catalysts. ϕSDsurface/bulk enables a quantitative evaluation and comparison of distinct catalyst synthesis routes in terms of their ratio of accessible metal sites. It gives guidance for further optimization of the accessible site density of M–NC catalysts.

Atomically dispersed Ru in Pt3Sn intermetallic alloy as an efficient methanol oxidation electrocatalyst.

We successfully fabricate a novel concave nanostructure that is composed of atomically dispersed Ru atoms in Pt3Sn nanoconcaves (Ru-Pt3Sn NCs), which shows enhanced performance in methanol electroxidation compared to commercial Pt/C. This could be ascribed to the stable intermetallic structure and active surface structure, as well as the synergy among Pt, Sn and Ru.

Mechanism on catalytic cracking tar with CaO-based catalysts for hydrogen-rich gas by DFT and experiments

As the model compound of tar, the catalytic cracking performances of toluene with CaO-based catalysts were studied by DFT simulation and fixed bed experiment. The DFT results showed the adsorption energy of toluene on (1 0 0) surfaces increased as FC < CaO < NC < NFC at 650 °C. The optimal reaction path for toluene to dissociate H was obtained in the process of toluene cracking using NC and NFC catalysts. The NC catalyst doped with Fe enhanced the catalytic activity of Ni, and the rate determining step reaction activation barrier to generate H2 was decreased from 1.50 eV to 0.58 eV. And the activation barrier for CH4 formation was higher than that for H2, which promoted the cracking reaction to produce H2. The experimental results showed that the catalytic toluene cracking effect of NFC was the best among the four catalysts at 650 °C, with 98.11% conversion rate and 93.11% H2 yield. Compared with NC, H2 yield was increased by 27.92%, CH4 yield was decreased by 50.43%. Thermogravimetric results showed that NFC was less likely to be inactivated due to carbon deposition than NC. NFC will be a kind of compound catalyst for tar cracking with high efficiency.

Structural Advantage Induced by Zinc Gluconate: Hierarchically Porous Carbon with In‐Situ Growth Iron‐Inside Carbon Nanotubes for Efficient Oxygen Reduction Reaction

AbstractHigh performance of Fe‐N−C electrocatalysts with excellent activity and durability are the most promising alternatives to replace the costly Pt‐based catalysts to catalyze the sluggish oxygen reduction reaction (ORR) kinetics at present. Herein, a zinc gluconate engaged strategy was reported to prepare iron‐inside carbon nanotube Fe‐N−C composites (Fe‐CNTs/NC), in which the zinc could be volatile in the process of high‐temperature pyrolysis and promoted in situ grown the iron‐inside carbon nanotubes in porous carbon matrix. The Fe‐CNTs/NC catalyst, benefiting from the hierarchical porous structure and abundant active sites, exhibits superior electrocatalytic performance (half‐wave potential of 0.838 V) and stability (9.31 % decay after a 20 000 s continuous test) in alkaline media compared to commercial Pt/C (half‐wave potential of 0.824 V and 13.15 % of stability decay rate under the same conditions). This study provides novel insights into the construction of carbon materials with dispersed active sites and hierarchically porous structure for electrocatalytic applications.

In situ confinement pyrolysis of ZIF-67 nanocrystals on hollow carbon spheres towards efficient electrocatalysts for oxygen reduction

The design and preparation of metal-organic frameworks (MOFs) as self-sacrificed precursors/templates has been considered as a promising strategy in recent years for fabricating metal/carbon electrocatalysts with intriguing architectures and outstanding properties. However, the serious aggregation during the calcination and the poor electron conductivity are still obstacles for these electrocatalysts which need to be urgently solved. Herein, an in situ confinement pyrolysis protocol is reported to transform ZIF-67 nanocrystals on hollow carbon spheres (HCS) to cobalt and nitrogen-enriched carbon shell, resulting in the formation of hierarchical HCS@Co/NC. This is the first study of electrochemistry for HCS decorated with MOFs or MOFs derivatives. In the structure, metallic Co nanoparticles (NPs) and N species are strongly anchored and dispersed in the network of nanocarbon shell, which not only affords a boosting conductivity but also greatly alleviates the aggregation of active sites. Meanwhile, the unique structure with hollow feature provides an effective pathway for mass transport and shortens the transmission path of electrons. Thanks to the advantages of structure and composition, the HCS@Co/NC catalyst exhibits a superb performance of oxygen reduction reaction, which outperforms the commercial Pt/C benchmark.

Oxidative Esterification of 5-Hydroxymethylfurfural with an N-doped Carbon-supported CoCu Bimetallic Catalyst.

The direct fabrication of furan-2,5-dimethylcarboxylate (FDMC), a promising renewable monomer, from biomass-derived 5-hydroxymethylfurfural (HMF) is a cutting-edge process. In this contribution, an elaborately designed N-doped carbon-supported CoCu bimetallic catalyst (Cox Cuy -NC; x/y=9:1, 7:3, 4:6, which represents the designed molar ratio of Co and Cu in the catalyst), which could offer a desirable FDMC yield of 95 % under mild and base-free conditions (Co7 Cu3 -NC, 2 bar O2 , 80 °C, 4 h) is described for the oxidative esterification of HMF. Notably, an FDMC formation rate of 6.1 molFDMC molCo -1 h-1 was achieved over Co7 Cu3 -NC, which represents the highest catalytic efficiency so far among Co-based catalytic systems. It has been demonstrated that Cu-doping in Co7 Cu3 -NC catalyst brings about more active sites (Co-Nx species) with stronger molecular oxygen activation ability. The increase of surface N content of Co7 Cu3 -NC also improves basicity of the catalyst, which favors the hydrogen abstraction process during the HMF oxidative esterification reaction. These findings may pave an efficient and green way for the synthesis of sustainable bio-based polymer monomers.

Carbon-nanotube-grafted and nano-Co3O4-doped porous carbon derived from metal-organic framework as an excellent bifunctional catalyst for zinc–air battery

In this study, carbon-nanotube (CNT)-grafted and nano Co3O4-doped porous carbon was prepared by the carbonization of a synthesized zeolitic imidazolate framework compound (ZIF-67/ZIF-8) followed by an oxidation treatment. The novel catalyst demonstrated excellent ORR and OER because of the Co3O4 nanoparticles and nitrogen-doped in the carbon framework (NC). In addition, the carbon nanotube grafted on the framework provided a good electrical conductivity while the carbon framework matrix provided a porous skeleton which is beneficial for the mass transfer of electrolyte. In the ORR study, the novel catalyst, CNT-Co3O4/NC, showed a half-wave potential of −0.124 V at 0.1 M KOH (Pt/carbon: −0.152 V) while the limited current density is 4.84 mA/cm2 (Pt/carbon: 4.9 mA/cm2). In terms of OER performance, the potential is 0.819 V at current density of 10 mA/cm2 (Ir/carbon: 0.771 V). The CNT-Co3O4/NC catalyst shows a specific capacitance of 814 mAh/g (1.19 V at 50 mA/cm2), which is very close to the theoretical capacitance (820 mAh/g) and the maximum power density was 267 mW/cm2 (0.746 V at 385 mA/cm2) while 255 mW/cm2 (0.711 V at 360 mA/cm2) was obtained using Pt/carbon catalyst. We believe that the novel CNT-Co3O4/NC can be used as an excellent catalyst in the zinc-air battery.

Insights into facet-dependent reactivity of CuO–CeO2 nanocubes and nanorods as catalysts for CO oxidation reaction

Copper–ceria (CuO–CeO2) catalysts have been known to be very effective for the oxidation of CO, and their chemical behavior has been extensively studied during the last decades. However, the effect of different CeO2 crystal surfaces on the catalytic activity of CuO–CeO2 for the oxidation of CO is still unclear and should be further elucidated. In this study, we deposited 1 wt% Cu on mostly {100}-exposed CeO2 nanocubes (1CuCe NC) and mostly {110}-exposed CeO2 nanorods (1CuCe NR), respectively. Both 1CuCe NC and 1CuCe NR have been used as catalysts for the oxidation of CO and achieved 100% and 50% CO conversion at 130 °C, respectively. The differences in the catalytic activity of 1CuCe NC and 1CuCe NR were analyzed using temperature-programmed reduction of H2 and temperature-programmed desorption of CO techniques. The results confirmed the excellent reducibility of the 1CuCe NC catalyst, which was attributed to the weak interactions between Cu and the CeO2 support. Moreover, in situ diffuse reflectance infrared Fourier-transform spectroscopy studies indicated that the {100} planes of 1CuCe NC facilitated the generation of active Cu(I) sites, which resulted in the formation of highly reactive Cu(I)-CO species during the oxidation of CO. Both the excellent redox properties and effective CO adsorption capacity of the 1CuCe NC catalyst increased its catalytic reactivity.