Supported Cobalt Oxide Research Articles

Ultrathin veil-like SnO2 supported Co3O4 nanoparticles for direct borohydride fuel cell anode

In direct borohydride fuel cell (DBFC), there is a contradiction between catalytic activity and specific discharge capacity (SDC) owing to the dual catalytic effects of most anode catalysts on both borohydride oxidation reaction (BOR) and borohydride hydrolysis reaction (BHR). To overcome this problem, a facile method to fabricate an ultrathin tin dioxide (SnO2) supported cobalt oxide (Co3O4) composite material (u-SnO2/Co3O4) as DBFC anode catalyst was developed. Both catalytic ability for BOR and specific discharge capacity of the DBFC using the u-SnO2/Co3O4 (DBFC-u-SnO2/Co3O4) with 5–10 nm thick two-dimensional (2D) SnO2 were improved. The maximum power density (52.5 mW cm−2) and SDC (1380 mAh g−1) of DBFC-u-SnO2/Co3O4 were respectively increased by 105% and 1740% in comparison with those of DBFC with Co3O4 as anode catalyst (DBFC-Co3O4). The u-SnO2/Co3O4 has higher specific surface area, electron donation ability, and the rate of desorption of intermediate product (such as BH3OH−, Hads) which may account for the excellent catalytic performance of u-SnO2/Co3O4 for BOR.

Development and characterization of silica supported cobalt oxides for ethanol oxidation using different preparation methods

Cobalt oxide in spinel structure (Co3O4) is an efficient catalyst for ethanol oxidation due to its potential as an oxygen source. To enhance the catalytic performance, Co3O4 is dispersed on silica (SiO2). The degree of dispersion and form of oxides on the support depend on the preparation method. The objective of this work is to compare physicochemical properties and catalytic performance in ethanol oxidation of silica-supported cobalt catalysts from different preparation methods. The catalysts were prepared by incipient wetness impregnation (IP), precipitation with reverse micelle (RM), and precipitation with NH4OH (PN) methods. The forms and dispersion of cobalt species were investigated by X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS) and X-ray photoelectron spectroscopy (XPS). The cobalt species from RM and IP methods were mainly Co3O4, but that from PN method was the mixed phases of Co3O4, CoO and Co2SiO4. The RM method provided the best dispersion of Co3O4, surface Co3+ and lattice O2− on SiO2. Consequently, the catalyst from RM method provided the highest ethanol conversion and CO2 yield from all temperature ranges.

Identifying properties of low-loaded CoOX/CeO2 via X-ray absorption spectroscopy for NO reduction by CO

The speciation and catalytic activity of ceria supported transition metal oxides synthesized via incipient wetness impregnation are highly dependent on synthesis parameters such as the choice of metal precursor and the concentration of defects such as oxygen vacancies in the support. Here, cobalt oxide domains were synthesized on cerium oxide nanorods and commercial nanopowder via incipient wetness impregnation of cobalt (II) nitrate hexahydrate, cobalt (II) acetate, cobalt (III) acetylacetonate, and disodium cobalt (II) ethylenediaminetetraacetic acid at surface densities below monolayer coverage. Their reactivity was tested in the catalytic reduction of NO by CO. The steady-state deNOx activity at 250 °C of the catalyst prepared with cobalt (III) acetylacetonate and ceria nanorods was nearly three times greater than that of the control catalyst. From X-ray absorption spectroscopy it was seen that as-deposited cobalt precursors on a nanorod support were more highly coordinated than were cobalt precursors on comparable commercial ceria nanoparticles, possibly indicating anchoring at defects on the nanorods. A relationship was found between catalyst activity and the cobalt oxidation state of the fully calcined catalysts that suggests that deNOx activity is separately dependent on the cobalt oxide distribution and the presence of defects in the support. Overall, here it is shown that the two critical synthesis parameters of ligand choice and defected supports combine additively to improve reactivity of the supported cobalt oxide.

Hydrophobic Modification of Microenvironment of Highly Dispersed Co3O4 Nanoparticles for the Catalytic Selective Oxidation of Ethylbenzene

AbstractMicroenvironments in enzymes play crucial roles in controlling the activities of active centers. Here, hexagonal mesoporous silicas (HMS) with hydrophobic microenvironment was used to mimic the enzymes on the hydrocarbon oxidation with cobalt oxides incorporated as active sites. The variation of the structure and surface properties of the materials with phenyl group incorporation and the state of the supported cobalt oxides were carefully studied. It showed that cobalt oxides presented as Co3O4 distributed evenly among the support, and the catalytic microenvironment was modified by the neighboring phenyl groups to be hydrophobic. This novel catalyst showed enhancement in the adsorption of ethylbenzene and in turn promoted the catalytic conversion than the hydrophilic one. 55.1 % conversion of ethylbenzene and 86.1 % selectivity for acetophenone could be obtained at 393 K for 6 h under 1.0 MPa of O2 with free solvent. Hydrophobic microenvironment of pore surface was considered as an important factor for the better catalytic activity.

Preparation, formulation and deposition of mica flake supported cobalt oxide for nanostructured lithium ion battery anodes

We describe the fabrication and morphological and electrochemical characterisation of lithium ion battery anodes whereby the active material is supported on flake-like microparticles. Using various physical analytical techniques we verify that nanostructured cobalt (II, III) oxide can be directly grown onto commercial titanium dioxide-coated mica flakes by a liquid phase oxidation route. We then investigate the formulation and deposition of this material along with carbon black in order to form electrodes. Here we consider two binder/solvent systems, one widely used based on polyvinylidene fluoride in N-methy-2-pyrrolidone, and one more recently identified based on sodium alginate in water. We show that the latter system is preferable for the formation of anodes using the cobalt oxide coated flake-like particles as it leads to a more homogeneous distribution of active and conductive material in the electrode. Using cyclic voltammetry and electrochemical impedance spectroscopy we show that this feature improves the access to active material and facilitates efficient charge transfer in the electrode while maintaining electrode integrity. Moreover, an electrode based on the alginate binder exhibited a high reversible specific capacity of 650 mAh/g along with 84.8% capacity retention after 70 cycles. Overall our study indicates the promise of including shape anisotropic particles such as microflakes in battery electrodes.

Robust carbon-coupling catalysts with no precious metals

A new, precious-metal-free catalyst could lower the cost of making synthetic fuels—and it even outperforms commercial catalysts when it comes to knitting together new carbon-carbon bonds using a common synthetic process. Fischer-Tropsch (F-T) synthesis is a century-old process for converting mixtures of CO and hydrogen, generally derived from natural gas and coal, to transportation fuels and other hydrocarbons. The process can be used to make fuels when crude oil is unavailable and can make fuels that are purer and higher performing. The F-T process, which generates tens of millions of liters of fuel per day, relies on oxide-supported cobalt, iron, and ruthenium catalysts. Cobalt is the most common choice, especially when the feedstock is natural gas. Manufacturers often run the F-T process in slurry reactors, in which the solid catalyst and gas-phase reactants are stirred in a liquid. These reactors can provide energy and heat-management advantages relative to other types

Mesoporous Co3O4 as a New Catalyst for Allylic Oxidation of Cyclohexene

Mesoporous cobalt oxide was investigated for the liquid phase oxidation of cyclohexene using tertiobutylhydroperoxide (TBHP) as an oxidant. The results were compared with several series of supported cobalt catalysts to study the influence of the cobalt loading and solvents on the overall conversion and selectivity. Mesoporous cobalt was synthesized through the nanocasting route using siliceous SBA-15 mesoporous material as a hard template and cobalt nitrate as the cobalt oxide precursor. Supported cobalt oxide catalysts (Co/MxOy) were synthesized by the impregnation method using two loadings (1 and 5 wt.%) and Al2O3, TiO2, and ZrO2 as supports. Samples were characterised by means: elemental analysis, X-ray powder Diffraction (XRD), BET (surface area), UV-Vis DR Spectroscopy, and MET. The results obtained showed that the cobalt oxide retains the mesoporous structure of SBA-15, and in all Co/MxOy, crystalline Co3O4 and CoO phases are observed. The mesoporous cobalt oxide is more active than the supported cobalt catalysts in the allylic oxidation of cyclohexene, with a conversion of 78 % of cyclohexene and 43.3 % selectivity toward 2-cyclohexene-1-ol. The highest activity of mesoporous cobalt oxide could be ascribed to its largest surface area. Furthermore, Co3O4 has both Lewis and Brönsted acidic sites whereas Co/MxOy has only Lewis acidic sites, which could also explain its superior catalytic activity. Moreover, mesoporous cobalt oxide was more stable than supported cobalt catalysts. Therefore, this catalyst is promising for allylic oxidation of alkenes.

Engineering of activated carbon surface to enhance the catalytic activity of supported cobalt oxide nanoparticles in peroxymonosulfate activation

Commercial activated carbon has been functionalized by chemical or thermal treatments to introduce surface oxygen functional groups able to anchor small cobalt nanoparticles with superior catalytic activity for peroxymonosulfate activation. The resulting activated carbon supports where characterized by combustion elemental analysis, Fourier-transformed infrared spectroscopy, Raman spectroscopy, isothermal N2 adsorption, temperature programmed desorption/mass spectrometry, X-ray diffraction and scanning electron microscopy. Activated carbon functionalization by nitric acid resulted the most appropriated method to provide a higher population of oxygenated functional groups able to anchor small cobalt nanoparticles. The catalytic activity of supported oxidized metal nanoparticles (4.7 ± 0.05 nm) was higher than analogous non-oxidized cobalt nanoparticles (2.9 ± 0.14 nm). The use of analogous supported oxidized iron or copper nanoparticles resulted in lower catalytic activity. Importantly, the supported oxidized cobalt nanoparticles at 0.2 wt% loading exhibit higher activity than benchmark catalysts such as unsupported Co3O4 solid or even homogeneous Co2+ ions. This is a reflection of the relatively low estimated activation energy for both processes, peroxymonosulfate decomposition and phenol degradation. The estimated activation energy values are about 30 and 32 kJ mol−1. The stability of the most active catalyst was assessed by performing eight consecutive uses without observing decrease of catalytic activity, neither metal leaching or metal nanoparticle aggregation. Turnover numbers/turnover frequencies values as high as 4·105/8·105 h−1 for peroxymonosulfate activation and 39·103/68·103 h−1 for phenol degradation at pH 7 and 20 °C have been estimated, respectively. Electron paramagnetic resonance measurements and selective quenching experiments revealed that the generated sulfate radicals from peroxymonosulfate rapidly are transformed in highly reactive hydroxyl radicals. In excellent agreement with previous reports, this work demonstrates the importance of an adequate activated carbon functionalization to obtain superior and stable catalysts for peroxymonosulfate activation.

Effect of pH, Acid and Thermal Treatment Conditions on Co/CNT Catalyst Performance in Fischer–Tropsch Reaction

Multiwalled carbon nanotubes (CNT) supported cobalt oxide was prepared as a catalyst by strong electrostatic adsorption (SEA) method. The CNT support was initially acid- and thermal-treated in order to functionalize the support to uptake more Co clusters. The Co/CNT were characterized by a range of analytical methods including transmission electron microscopy (TEM), temperature programmed reduction with hydrogen (H2-TPR), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, atomic absorption spectroscopy (AAS), Zeta sizer particle size analysis and Brunauer–Emmett–Teller (BET) surface area analysis. TEM images showed cobalt particles were highly dispersed and impregnated at both exterior and interior walls of the CNT support with a narrow particle size distribution of 6–8 nm. In addition, the performance of the synthesized Co/CNT catalyst was tested using Fischer–Tropsch synthesis (FTS) reaction which was carried out in a fixed-bed micro-reactor. H2-TPR profiles indicated the lower reduction temperature of 420 °C was required for the FTS reaction. The study revealed that cobalt is an effective metal for Co/CNT catalysts at pH 14 and at 900 °C calcination temperature. Furthermore, FTS reaction results showed that CO conversion and C5+ selectivity were recorded at 58.7% and 83.2% respectively, which were higher than those obtained using a Co/CNT catalyst which pre-treated at a lower thermal treatment temperature and pH.

Synthesis, characterisation and water-gas shift activity of nano-particulate mixed-metal (Al, Ti) cobalt oxides.

The formation of mixed-metal cobalt oxides, representing potential metal-support compounds for cobalt-based catalysts, has been observed at high conversion levels in the Fischer-Tropsch synthesis over metal oxide-supported cobalt catalysts. An often observed increase in the carbon dioxide selectivity at Fischer-Tropsch conversion levels above 80% has been suggested to be associated to the formation of water-gas shift active oxidic cobalt species. Mixed-metal cobalt oxides, namely cobalt aluminate and cobalt titanate, were therefore synthesised and tested for potential catalytic activity in the water-gas shift reaction. We present a preparation route for amorphous mixed-metal oxides via thermal treatment of metal precursors in benzyl alcohol. Calcination of the as prepared nanoparticles results in highly crystalline phases. The nano-particulate mixed-metal cobalt oxides were thoroughly analysed by means of X-ray diffraction, Raman spectroscopy, temperature-programmed reduction, X-ray absorption near edge structure spectroscopy, extended X-ray absorption fine structure, and high-resolution scanning transmission electron microscopy. This complementary characterisation of the synthesised materials allows for a distinct identification of the phases and their properties. The cobalt aluminate prepared has a cobalt-rich composition (Co1+xAl2-xO4) with a homogeneous atomic distribution throughout the nano-particulate structures, while the perovskite-type cobalt titanate (CoTiO3) features cobalt-lean smaller particles associated with larger ones with an increased concentration of cobalt. The cobalt aluminate prepared showed no water-gas shift activity in the medium-shift temperature range, while the cobalt titanate sample catalysed the conversion of water and carbon monoxide to hydrogen and carbon dioxide after an extended activation period. However, this perovskite underwent vast restructuring forming metallic cobalt, a known catalyst for the water-gas shift reaction at temperatures exceeding typical conditions for the cobalt-based Fischer-Tropsch synthesis, and anatase-TiO2. The partial reduction of the mixed-metal oxide and segregation was identified by means of post-run characterisation using X-ray diffraction, Raman spectroscopy, and transmission electron microscopy energy-dispersive spectrometry.

Photocatalytic oxidation of glucose in water to value-added chemicals by zinc oxide-supported cobalt thioporphyrazine

Efficient photocatalytic oxidation of glucose into value-added chemicals was achieved by ZnO/CoPzS8 composite in water, the presence of CoPzS8 changed the glucose reaction pathway and glucaric acid was obtained in this photocatalytic system.

Reduced graphene oxide-supported cobalt oxide decorated N-doped graphitic carbon for efficient bifunctional oxygen electrocatalysis.

A high-performance composite bifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has been synthesized via in situ growth of a hybrid precursor of graphene oxide (GO) and cobalt-based zeolite imidazolium framework (ZIF-67) under hydrothermal condition, followed by calcination at elevated temperature. The as-prepared composite bifunctional catalyst is confirmed to possess a structure of N-GC/Co@CoO/rGO, with core–shell nanoparticles of Co@CoO encapsulated in nitrogen-doped graphitic carbon (N-GC) thin layers which are then overall supported by reduced graphene oxide (rGO) sheets. With N-GC furnishing high population of ORR active sites, CoO being active for OER which is further enhanced by a highly conductive metal core, rGO sheets enhancing the overall electronic conduction, as well as the multiple synergistic couplings in the composite materials, pronounced ORR and OER catalytic activities with superior stability have been achieved. The catalysts also showed excellent tolerance to the crossover effect to methanol, showing great potential in energy-related applications requiring efficient oxygen electrocatalysis.

Graphene oxide-supported zinc cobalt oxides as effective cathode catalysts for microbial fuel cell: High catalytic activity and inhibition of biofilm formation

Microbial fuel cell (MFC) is a unique energy technology that can treat wastewater and concurrently generate electricity. However, the MFC performance is typically rather limited due to the sluggish kinetics of oxygen reduction reaction (ORR) and insufficient ion transfer on the cathode. Thus, development of high-performance ORR catalysts with enhanced ion transfer is of fundamental significance for the wide-spread application of MFC. In this study, nanocomposites (GO-Zn/Co) based on graphene oxide-supported cobalt and zinc oxide nanoparticles were synthesized by a hydrothermal treatment of graphene oxide and cobalt and zinc acetates followed by pyrolysis at controlled temperatures. The porosity of the resulting nanocomposites was found to vary with the pyrolysis temperature and Zn/Co mole ratios. The sample prepared at 800 °C with a Zn/Co mole ratio of 1:1 exhibited the best ORR performance in alkaline media among the series, with a high halfwave potential of + 0.81 V vs. RHE. Notably, the resultant GO-Zn/Co nanocomposites exhibited an apparent antibacterial activity, inhibiting the formation of biofilms on the cathode surface. An MFC using the as-prepared GO-Zn/Co as the cathode catalyst achieved a maximum power density (773 mW m−2) that was even higher than that with state-of-art Pt/C catalyst (744 mW m−2), and the power output remained virtually unchanged during continuous operation for one month. The results suggest that the GO-Zn/Co nanocomposites can serve as a viable alternative for MFC cathode catalysts.

Synthesis of cobalt–nitrogen-doped mesoporous carbon from chitosan and its performance for pollutant degradation as Fenton-like catalysts

Supported cobalt oxides on mesoporous nitrogen-doped carbon (CoxOy/NC) were prepared by a simple pyrolysis method using cobalt acetate as the cobalt source and chitosan as the nitrogen and carbon source. The as-synthesized catalysts were characterized by XRD, N2 adsorption/desorption, SEM, TEM and XPS. It was found that chitosan was transformed to mesoporous carbon after pyrolysis at 900 °C under N2 atmosphere, while Co2+ was reduced to metallic Co covering with cobalt oxide, which was uniformly distributed in the surface of carbon. The catalytic performances were examined by Acid Orange 7 (AO7) degradation with H2O2 as an oxidant in bicarbonate aqueous solution. The dye was decolorized completely after 20 min at room temperature with the CoxOy/NC catalyst. The catalyst can be recycled up to four times without significant loss of activity. The addition of methanol as a hydroxyl radical scavenger confirmed that the radicals take part in the reaction as the major active species. In addition, intermediate products were identified by electrospray ionization-mass spectrometry during the degradation of AO7.

Preparation and catalytic behavior of reduced graphene oxide supported cobalt oxide hybrid nanocatalysts for CO oxidation

Abstract The reduced graphene oxide (rGO) supported cobalt oxide nanocatalysts were prepared by the conventional precipitation and hydrothermal method. The as-prepared rGO-Co3O4 was characterized by the XRD, Raman spectrum, SEM, TEM, N2-sorption, UV-Vis, XPS and H2-TPR measurements. The results show that the spinel cobalt oxide nanoparticles are highly fragmented on the rGO support and possess uniform particle size, and the as-prepared catalysts possess high specific surface area and narrow pore size distribution. The catalytic properties of the as-prepared rGO-Co3O4 catalysts for CO oxidation were evaluated through a continuous-flow fixed-bed microreactor-gas chromatograph system. The catalyst with 30% (mass fraction) reduced graphene oxide exhibits the highest activity for CO complete oxidation at 100 °C.

Catalytic activity of different sizes of Ptn/Co3O4 in the oxidative degradation of Methylene Blue with H2O2

In this work, we demonstrate the catalytic activity and kinetic analyses of generation six poly(amido-amine) hydroxyl-terminated (PAMAM), G6-OH(Ptn) (n = 55, 140, 225) dendrimer-encapsulated nanoparticles (DENs) immobilized onto mesoporous cobalt oxide (Co3O4) for the catalytic oxidation of methylene blue (MB). Ultra-Violet Visible (UV–Vis) spectrophotometry showed the ligand to metal charge transfer (LMCT) band of metal precursor ions coordinated to the tertiary amines of the dendrimer. The size of fully reduced Pt DENs and supported Pt nanoparticles were investigated using High-Resolution Transmission Electron Microscopy (HR-TEM). The mesoporous Co3O4 was synthesized by inverse micelle method, prior to Ptn DENs being supported on the Co3O4 via wet impregnation procedure. The crystallite structure and size of Co3O4 was investigated by powder X-ray diffraction (p-XRD) spectroscopy. Immobilized Ptn/Co3O4 structural analysis was investigated for the pore size and pore volume using N2 sorption techniques. Thermal gravimetric analyses (TGA) also indicated the dendrimer decomposition on the G6-OH(Ptn)/Co3O4 materials to be 550 °C. Hydrogen temperature programmed reduction (H2-TPR) analyses were conducted and the reducibility of the supported cobalt oxide showed only one temperature peak that was ascribed to the reduction of surface lattice oxygens. The experimental kinetic data was analyzed and fitted to the Langmuir-Hinshelwood model using elementary first-order reaction kinetics and the thermodynamic parameters were calculated. Catalyst Pt55/Co3O4 showed stability during the reusability investigation of up to 8 cycles. The G6-OH(Ptn) were immobilized on silica and tested for catalytic oxidation of MB as a control experiment.

Graphene Oxide-Supported Cobalt Phthalocyanine As Highly Efficient Electrocatalysts for the Oxygen Reduction Reaction

The rapid depletion of oil reserves and the resulting environmental pollution have stimulated the development of clean and renewable alternative energy sources. Fuel cells, which own high efficiency and environmental advantages, have received great attention. 1 The main bottleneck of fuel cells lies in the sluggish kinetics of oxygen reduction reaction (ORR), which is the key process in the cathode. 2 High performance ORR catalysts are urgently desired. In order to reduce the cost of ORR catalyst and to promote the commercialization of fuel cells, many researchers have been exploring alternative low-cost non-precious metal catalysts (NPMCs) with attractive performance for ORR. Among these NPMCs materials, metal phthalocyanines (MPcs) have received a great deal of interest due to highly conjugated structure, chemical and thermal stability as well as low cost of preparation. 3 In addition, the catalytic activity and durability of MPcs can be improved by employing suitable electrocatalyst supports. In this work Cobalt Phthalocyanine (CoPc) was immobilized between layers of graphene oxide (GO) through non-covalent functionalization approach. Briefly, the catalyst ink was prepared using CoPc/GO, water, ethanol and Nafion. Electrodes were prepared by drop-casting over a Rotating Ring-Disc Electrode (RRDE electrode, glassy carbon disk with diameter of 5.61 mm and surface area of 0.2475 cm2 surrounded by a Pt ring with a surface area 0.1866 cm2). The RRDE technique with a three-electrode electrochemical cell was employed to study the ORR activity, using a Pine electrochemical system. A Ag/AgCl (3 M KCl) electrode, a Pt wire and the catalyst coated RRDE were used as reference electrode, counter electrode and working electrode respectively. All electrochemical tests were performed at room temperature in 0.1 M KNO3 solution. Cyclic voltammetry curves (CV) were recorded from 0.2 to -0.8 V until a steady state situation was reached in Ar-saturated and O2-saturated electrolyte. The scan rate was set at 20 mVs−1. For the ORR test, linear sweep voltammetry (LSV) curves were recorded at different electrode rotation speeds (100, 225, 400, 625, 900, 1225, 1600 rpm) in the oxygen saturated 0.1 M KNO3 at the same potential range with a scan rate of 5 mVs-1. The formation of a composite structure was revealed by the appearance of characteristics graphene oxide and phthalocyanine bands in the Raman spectra, as shown in Fig. 1a. The cyclic voltammograms (CVs) of CoPc/GO in Ar and O2-saturated 0.1 M KNO3 solution are shown in Fig. 1b. It can be seen that the composite exhibited only a double-layer capacitive behavior in Ar-saturated KNO3. In contrast, a cathodic peak emerged at -0.15 V for CoPc/GO in O2-Saturated electrolyte. This value is close to related for Pt/C and more positive than that observed for CoPc/3D-G in the literature, 4 indicating the good electrocatalytic abilities of CoPc/GO toward ORR. The polarization curves on CoPc/GO at different rotation speeds are shown in Fig. 1c. The disk current density increased with the increasing rotation rate, from 100 to 1600 rpm, due to the shortened diffusion distance at high speeds, and all reached well-defined diffusion limiting currents. The transferred electron number n of CoPc/GO at various potentials was further calculated by Koutecky-Levich (K-L) equation, as shown in Fig. 1d. The K-L plots have good linearity with a rather consistent slope, implying a similar n on CoPc/GO at different electrode potentials. The average number for n regarding the O2 reduction at CoPc/GO obtained from K-L plots is ∼3.7, indicating the near four-electron pathway during the ORR. The Eonset of CoPc/GO was + 0.02 V (at 1600 rpm). An enhancement in the catalytic activity of CoPc/GO was noticed by using GO as the support, demonstrating that the structure of GO and the strong π-π interaction between GO and CoPc was beneficial. Detailed characterizations of the composite are in progress to correlate its nanostructure with the superior electrochemical performance. T. Shimura, Z. Jiao, and N. Shikazono, J. Electrochem. Soc., 164, F1158 (2017). K. A. Kuttiyiel, Y. Choi, S.-M. Hwang, G.-G. Park, T.-H. Yang, D. Su, K. Sasaki, P. Liu, and R. R. Adzic, Nano Energy, 13, 442 (2015). A. B. Sorokin, Chemical Reviews, 113, 8152-8191 (2013). C. Sun, Z. Li, X. Zhong, S. Wang, X. Yin, and L. Wang, J. Electrochem. Soc., 165 (2), F24-F31 (2018) Figure 1

Rapid inkjet printing of high catalytic activity Co3O4/N-rGO layers for oxygen reduction reaction

The accurate and reproducible large-scale production of catalyst layers containing low-cost, abundant electrocatalysts gains in importance. Herein, pivotal factors are discussed that need to be considered when a combined inkjet printing and photonic curing platform is used as a promising fabrication method for catalyst layers based on a model low-cost catalyst, i.e., nitrogen-doped reduced graphene oxide supported cobalt oxide nano sheets (Co3O4/N-rGO), specifically prepared to formulate an inkjet ink. The ink is stable for weeks and can reproducibly be printed with piezoelectric printheads. Ink composition and printing parameters are optimized to achieve high-resolution printing and good adhesion on glassy carbon substrates. Polyvinylpyrrolidone and ethyl cellulose are used as catalyst stabilizers in the ink and must be removed through thermal post-processing to avoid a decrease of the electrical conductivity of the catalyst layer and a degradation of the catalytic activity of the Co3O4 nanocrystals. Conventional slow oven curing (i.e., hours) and photonic curing with a Xe flash lamp (seconds) are compared to generate temperatures above 400 °C under ambient conditions. Both techniques can increase the size of the Co3O4 nanocrystals from ∼7 nm up to ∼15 nm. Photonic curing with pulses above 2 J·cm–2 shot energy density initiates the reduction of the oxidation states of cobalt from (II,III) to (II). Residues and side products of polymeric stabilizers can be found using photonic curing pulses below 10 J·cm–2. This work highlights the advances made in digital printing and post-processing for catalyst layer production and demonstrates the importance of proper design of the ink, the printing and the post-processing for the large-scale production of catalyst layers for the ORR based on low-cost materials. The findings can be transferred to other metal and mixed metal oxide nanocatalysts.

Mechanochemical synthesis of supported cobalt oxide nanoparticles on mesoporous materials as versatile bifunctional catalysts

Supported Co3O4 nanoparticles on SBA-15 aluminosilicates (Al-SBA-15) with different cobalt loadings (0.5, 1, 5, 10 wt %) were synthesized by ball-milling. The synthesized materials were characterized by different techniques including, N2 adsorption measurements, XRD, TEM, EDX, ICP-MS, DRIFTs of pyridine among others. The catalysts were studied in the microwave assisted benzyl alcohol oxidation as well as in the akylation of toluene with benzyl chloride. Co3O4 catalysts exhibited moderate conversions in the selective oxidation of benzyl alcohol, with a high selectivity towards benzaldehyde. Lewis acidity increases upon the incorporation of cobalt nanoparticles onto the surface of the support which was found to significantly influence the materials in the alkylation of toluene with benzyl chloride. The high active sites accessibility of ball-milling prepared materials leads to high conversions to alkylated derivatives in short periods of time (>99 mol %, 30 min). A direct correlation acidity/activity could not be obtained in the systems, for which nanoparticle sizes and distribution could influence the observed activities.

Reduced Graphene Oxide-Supported Cobalt Phosphide Nanoflowers via in situ Hydrothermal Synthesis as Pt-Free Effective Electrocatalysts for Oxygen Reduction Reaction

Cobalt phosphide (CoP) has aroused extensive research interest in a field of electrochemical application due to its excellent catalytic activities. CoP and its compounds have been widely reported using in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, few reports about CoP as electrocatalysts for oxygen reduction reaction (ORR) were presented. In this work, we prepare reduced graphene-oxide(rGO)-loaded CoP (rGO@CoP) as an electrocatalyst for ORR through in situ hydrothermal treatment. The rGO@CoP as ORR catalyst exhibits excellent activities where its onset potential has a positive increase of 129[Formula: see text]mV, and the ORR potential achieves an increase of 330[Formula: see text]mV at a current density of 1.0[Formula: see text]mA[Formula: see text]cm[Formula: see text] compared with that of pure CoP. The current density is also significantly improved with an increase of 0.51[Formula: see text]mA[Formula: see text]cm[Formula: see text] at [Formula: see text]350[Formula: see text]mV, and the Tafel slope has a decrease of 19[Formula: see text]mV dec[Formula: see text]. Further tests show that the electron transfer number of rGO@CoP is 3.66, which is larger than 2.19 of pure CoP, indicating that it is dominated by a four-electron transfer pathway. Moreover, its stability (remained 98.6% current after working 6000[Formula: see text]s) and methanol tolerance are outstanding. These results show that rGO@CoP may be considered to replace traditional Pt-based ORR catalysts for fuel cells, and rGO loading has been proven to be an effective strategy to enhance the ORR performance of CoP, which may provide a new idea to synthesize transition metal phosphides as ORR catalysts.