Boosting electrocatalysis of oxygen reduction and evolution reactions with cost-effective cobalt and nitrogen-doped carbons prepared by simple carbonization of ionic liquids

Development of cost-effective, bi-functional carbon electrocatalysts via direct carbonization of ionic liquids (bis(cholinium) tetrachlorocobaltate(II) ([Ch]₂[CoCl₄]) and bis(1-butyl-3-methylimidazolium) tetrachlorocobaltate(II) ([Bmim]₂[CoCl₄])) is reported herein for the first time. Carbon electrocatalysts, dual-doped with cobalt and nitrogen, were tested for oxygen reduction (ORR) and oxygen evolution (OER) reactions. Both materials show high bi-functional catalytic activity and excellent stability due to synergistic effects arising from the presence of nitrogen and cobalt. Electrocatalyst prepared by carbonization of [Ch]₂[CoCl₄] show exceptional activity and selectivity toward ORR. Conversely, electrocatalyst prepared from [Bmim]₂[CoCl₄] showed a slightly better OER performance indicating that different catalytic sites are responsible for O₂ reduction and H₂O oxidation. Parent CoO particles with graphitic nitrogen boost activity for ORR, while elemental Co supported by nitrogen atoms is responsible for OER activity. Finally, energy consumption during electrolytic oxygen production was calculated revealing energy saving when using two materials as anode electrocatalysts.     

Electrocatalytic activity of platinum nanoparticles supported on different phases of tungsten carbides for the oxygen reduction reaction

Carbon-supported tungsten carbides with cubic (β-WC_1-x/C) and hexagonal (α-WC/C) are evaluated as support materials of Pt-nanoparticles, to be used as electrocatalysts for the oxygen reduction reaction (ORR) in acid media. The produced materials are characterized by X-Ray diffraction (XRD), energy dispersive X-ray spectroscopy, (EDS), X-ray photoelectron spectroscopy (XPS), in situ X-ray absorption near edge structure (XANES), and transmission electron microscopy (TEM). Cyclic voltammetry and polarization measurements on stationary and rotation disk electrodes are employed for the electrochemical investigations. It is seen that all Pt-α-WC/C catalysts present specific activity for the ORR similar to that of a standard carbon supported Pt catalyst (Pt/C), while for the Pt-β-WC_1-x/C composites the specific activitiy is 3.6 times higher than that of Pt/C, when a carbide-to-carbon load of 40 wt% is used. These differences in reactivity for the ORR may be associated to differences in the binding energy of adsorbed oxygen on Pt, introduced by the tungsten carbide substrates. Pt XANES results for the β-WC/C_1-x materials evidence a small increase in the Pt 5d band occupancy, which may lead to a weaker Pt-OH_x interaction, increasing the ORR kinetics.     

High efficiency platinum nanoparticles based on carbon quantum dot and its application for oxygen reduction reaction

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Efficient four-electron transfer platinum-based oxygen reduction catalysts: A mini review

Hydrogen fuel cell vehicles have attracted extensive attention for conversion equipment and new energy storage technologies. As an important component of hydrogen fuel cell vehicles, highly stable and active platinum-based (Pt-based) catalysts with 4-electron oxygen reduction reaction (ORR) selectivity are extremely important for promoting the application of this field. In this mini review, based on the ORR mechanism, the feasible strategies to enhance the catalytic stability and 4-electron selectivity of Pt-based catalysts were summarized. Furthermore, the effect mechanisms of each strategy in enhancing catalytic activity and 4-electron selectivity were emphatically discussed and their superiorities and limitations were evaluated. Finally, the research direction and current challenges of Pt-based catalysts were prospected from the perspective of their practical application in hydrogen fuel cell vehicles.     

Oxygen reduction on carbon supported Pt-W electrocatalysts

The catalytic activity of Pt-W electrocatalysts towards oxygen reduction reaction (ORR) was studied. Pt-W/C materials were prepared by thermolysis of tungsten and platinum carbonyl complexes in 1-2 dichloro-benzene during 48 h. The precursors were mixed to obtain relations of Pt:W: 50:50 and 80:20%w, respectively. The Pt carbonyl complex was previously synthesized by bubbling CO in a chloroplatinic acid solution. The synthesized materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV) and a rotating disk electrode (RDE). The results show that both materials (Pt₅₀W₅₀/C and Pt₈₀W₂₀/C) have a crystalline phase associated with metallic platinum and an amorphous phase related with tungsten and carbon. The particle size of the electrocatalysts depends on the relationship between platinum and tungsten. Finally, both materials exhibit catalytic activity for oxygen reduction.     

Heat-treated platinum nanoparticles embedded in nitrogen-doped ordered mesoporous carbons: Synthesis, characterization and their electrocatalytic properties toward methanol-tolerant oxygen reduction

Fabrication of N-doped ordered mesoporous carbons containing well-dispersed and methanol-tolerant Pt nanoparticles (Pt-NOMC) via an easy route is reported in this paper. These Pt-NOMC samples invoke the pyrolysis of co-fed carbon sources and Pt precursor with various carbonization temperatures (Pt-NOMC-T) in 3-[2-(2-Aminoethylamino)ethylamino]propyl-functionalized mesoporous silicas which were simultaneously used as N sources and hard templates. A series of different spectroscopic and analytical techniques was performed to characterize these Pt-NOMC-T catalysts. Combined the results from X-ray diffraction, N₂ adsorption-desorption isotherms, transmission electron microscopy and elemental analysis show that ca. 0.7-2.2 wt% of nitrogen was successfully doped on the high surface areas of ordered mesoporous carbon rods. Further studies by X-ray photoelectron spectroscopy indicated that Pt-NOMC-T catalysts with different ratios of quaternary-N and pyridinic-N were observed. Among various Pt-NOMC-T samples, the Pt-NOMC-1073 sample, which may be due to moderate electrical conductivity of ordered mesoporous carbons, unique nanostructure between Pt nanoparticles and N-doped carbon supports, and presence of more pyridinic-N atoms, was found to possess superior electrocatalytic activity for methanol-tolerant oxygen reduction in comparison with the typical commercial electrocatalyst (Pt/XC-72).     

Electrocatalytic activity of Pt nanoparticles electrodeposited on amorphous carbon-coated silicon nanocones

This study pulse-electrodeposits Pt nanoparticles on amorphous carbon-coated silicon nanocones (ACNCs) and explores them as the electrocatalyst for methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) for direct methanol fuel cell applications. The work prepares silicon nanocones on the Si wafer using porous anodic aluminum oxide as the template and then deposits the amorphous carbon layer on the nanocones by microwave plasma chemical vapor deposition. According to Raman scattering and X-ray photoelectron spectroscopies (XPS), the surface of the ACNC support is composed of a nanocrystalline graphitic structure, and rich in oxygen-containing adspecies. The Pt nanoparticles pulse-electrodeposited on the highly ordered ACNC support disperses well with a large electrocatalytic surface area. The Pt/ACNC electrode exhibits excellent electrocatalytic activity and stability toward both MOR and ORR. This study suggests the abundant oxygen-containing surface species and the nanometer size of the Pt catalyst as the two major factors enhancing electrocatalytic performance of Pt/ACNC electrode. The XPS study suggests the occurrence of charge transfer from π-sites of the graphitic structure to the Pt nanoparticle, thereby improving the electrochemical stability of the electrode.     

Methanol oxidation efficiencies on carbon-nanotube-supported platinum and platinum-ruthenium nanoparticles prepared by pulsed electrodeposition

Dense carbon nanotubes (CNTs, 30-50 nm in diameter, 6-8 μm in length) were grown via a thermal chemical vapor deposition process on titanium treated carbon cloths. Catalysts in the form of either nano-scale platinum (Pt) or platinum-ruthenium (Pt-Ru) particles were then deposited on the CNT surfaces by pulse-mode potentiostatic electrodeposition. Surface morphologies of the prepared electrodes were examined by scanning electron microscopy and transmission electron microscopy. Well dispersed catalysts, Pt alone (particle sizes of 7-8 nm) or Pt-Ru (particle sizes of 3-4 nm) nanoparticles, were successfully electrodeposited on the CNT surfaces in citric acid aqueous solutions. In addition, electrochemical characteristics of the specimens were investigated by cyclic voltammetry in argon saturated sulfuric acid aqueous solutions and in mixed sulfuric acid and methanol aqueous solutions. The catalytic activity of the Pt-Ru/CNTs electrode for methanol oxidation was 1038.25 A g⁻¹_Pt in a mixed solution containing 0.5 M sulfuric acid and 1.0 M methanol.     

Nitrogen-doped carbon xerogels catalyst for oxygen reduction reaction: Improved structural and catalytic activity by enhancing nitrogen species and cobalt insertion

Highly active nitrogen-doped carbon xerogel (N-CX) electrocatalysts for the oxygen reduction reaction (ORR) were synthesized through a simple sol-gel method. The N-CX samples are prepared using resorcinol – formaldehyde resin as the carbon precursor and dicyandiamide as the nitrogen precursor. The N-CX samples carbonized at different temperatures are inspected to interpret the effect of the high-temperature conditions towards the structures and ORR activity of the final products. As-prepared N-CX samples with different carbonized temperatures are characterized via X-ray photoelectron spectroscopy (XPS), X-ray diffractometry and Raman spectroscopy. The N-CX sample carbonized at 800 °C demonstrated the greatest ORR activity, and the structural properties and catalytic activities of the catalyst are then further improved by insertion of cobalt metal under an ammonia atmosphere. Metal doping evidently promotes the catalytic activity of the N-CX catalyst. Raman and XPS studies show that cobalt increases the creation of pyridinic-N and quaternary-N groups through the formation of more graphitic structures. The ammonia atmosphere is demonstrated to act as an additional N source by increasing the total N content in the carbon structure after high temperature treatment of the N-CX catalyst. Metal-N-like and metal carbide configurations generated play a role in catalyst production with high catalytic activity.     

Oxidized carbon/nano-SiC supported platinum nanoparticles as highly stable electrocatalyst for oxygen reduction reaction

Nano-SiC particles with derived carbon shells were prepared by an acid-etching method at room temperature. The mixture solutions of concentrated HF and HNO₃ were chosen to etch the nano-SiC particles, and an amorphous carbon shell absorbed by oxygen functional groups was formed on the SiC surface. The oxidized carbon/SiC (O-C/SiC) particles were used as supports for preparation of Pt electrocatalysts. The O-C/SiC supported Pt electrocatalysts showed a high catalytic activity and an excellent stability for oxygen reduction reaction. The improved stability can be ascribed to the anchoring effect of the carbon shell to Pt NPs and the high stability of nano-SiC core.     

Synthesis and characterization of platinum supported on surface-modified ordered mesoporous carbons by self-assembly and their electrocatalytic performance towards oxygen reduction reaction

Ordered mesoporous carbons (OMCs) were fabricated by an organic–organic self-assembly process. Surface-modified OMCs were also prepared via the conventional acid-oxidation, H₂O₂ oxidation and 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane (AEPTMS) grafted routes. Pt nanoparticles (NPs) supported on OMC (Pt/OMC) and modified OMC (Pt/OMC-H₂SO₄, Pt/OMC-H₂O₂ and Pt/OMC-AEPTMS) were synthesized and characterized by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), transmission electron microscopy (TEM) analysis. It was found that acid-oxidation (H₂SO₄/HNO₃) method led to formation of a much wider Pt distribution with mean particle size of 6.8 nm. Unlike Pt/OMC-H₂SO₄ samples, Pt NPs (ca. 2.0 nm) were supported uniformly on AEPTMS-modified OMC with low electrical conductivity. Among three surface-modified methods, the H₂O₂ treatment method was an easily controllable way for surface modification of OMC which possesses desirable electrical conductivity, well-dispersed and nanosized Pt (ca. 3 nm). Accordingly, the Pt/OMC-H₂O₂ samples were observed to have superior electrocatalytic activity for oxygen reduction reaction as compared to synthesized Pt/OMC, Pt/OMC-H₂SO₄, Pt/OMC-AEPTMS and the commercial electrocatalysts (Pt supported on XC-72).     

CoSe nanoparticles prepared by the microwave-assisted polyol method as an alcohol and formic acid tolerant oxygen reduction catalyst

CoSe catalyst supported on nanoporous carbon was synthesized by microwave heating of glycerol solutions of Co(II) acetate and sodium selenite. The electrocatalytic behavior of the CoSe/C for oxygen reduction reaction (ORR) and its tolerance to several alcohols and formic acid were investigated by rotating disk electrode voltammetry and the results were compared with those of Pt/C. The results indicate that CoSe/C is a highly selective electrocatalyst towards ORR and shows a very high degree of tolerance to the presence of formic acid, methanol, ethanol, 2-propanol and ethylene glycol in acid medium. For a 20 wt.% CoSe/C, the onset potential and the magnitude of the current for ORR were almost the same with or without the presence of these fuels. In contrast, the Pt/C catalyst exhibited a mixed potential due to the simultaneous oxidation of the fuels and reduction of oxygen, which in turn caused the onset potential for the ORR to shift cathodically by ca. 500 mV in the presence of these fuels. Electrochemical measurements showed that the synthesized CoSe/C catalyst had a four-electron transfer mechanism for ORR. It is expected that this low cost electrocatalyst with its almost full tolerance and multi-fuel capability can find application in conventional and mixed-reactant fuel cells fueled with low molecular weight alcohols or formic acid.     

Nanocomposite of platinum and prussian blue: A highly active and stable electrocatalyst towards oxygen reduction reaction in acidic media

Deployment of proton exchange membrane fuel cells (PEMFCs) are of vital importance for the mitigation of fossil energy shortage and environment pollution. A significant amount of Pt on cathode is highly needed to accelerate the process of sluggish oxygen reduction reaction (ORR) and maintains a stable long-term performance. During ORR, the yield of undesirable hydrogen peroxide through a two-electron pathway not only decreases outer power but also weakens the long-term stability. Herein, Pt-prussian blue (PB) composite, featuring around structure, is firstly proposed and facilely fabricated via electrostatic self-assembly strategy. Pt₁PB_0.25/C shows 50% higher activity than commercial Pt/C, rationally ascribed to modulated electronic structure and higher selectivity towards four-electron pathway. Moreover, in contrast with the striking 38% loss in mass activity for Pt/C after accelerated degradation tests (ADTs), Pt₁PB_0.25/C shows only a 15% decrease possibly due to the elimination of hydrogen oxide and the anchor interaction between Pt and PB. The employment of PB with a synergy role paves an efficient way for the fabrication of brand-new Pt-based catalysts with high activity and stability.     

Oxygen reduction reaction on nanostructured Pt-based electrocatalysts: A review

Pt deposition/anchoring technique and nature of the support influence the oxygen reduction reaction (ORR) activity in low-temperature proton exchange membrane fuel cells. Surface distribution, morphology (particle shape and size) of the deposited Pt nanoparticles (NPs) and physicochemical properties contribute to the electrocatalytic activity and durability of the catalyst. Investigations over the past two decades lead to various metal and metal oxide-based supports, along with advanced nanocarbon materials as suitable candidates since they play a vital role in defining surface morphology, particle-size distribution, crystallinity and electronic structure of the deposited Pt catalyst. Moreover, such supports improve the ORR activity and stability of the electrocatalyst due to their stronger interaction with the deposited Pt NPs. Briefly, a well-controlled and selective deposition of Pt NPs and designing of an excellent corrosion-resistant support for a promising ORR catalyst has gained more attention. Many advanced strategies are developed for the fabrication of atomically precise nanostructured Pt catalysts. This review summarises recent developments in the electrochemical, photochemical and physical deposition techniques for Pt NPs on various supports and their effects on the physicochemical properties and electrocatalytic activity towards the ORR.     

Oxygen reduction on platinum electrode coated with Nafion

The kinetics of the reduction of oxygen on platinum covered by a Nafion^® film in sulfuric acid (0.5 M) has been studied in order to determine to what extent the solid polymer electrolyte modifies this reaction. As electrode we used a rotating electrode which is particularly well adapted to the measurement of the permeability D_fC_f (product of the diffusion coefficient and of the oxygen concentration in the film) of oxygen in the Nafion^® film. This product is of the order of 6×10⁻¹² M cm⁻¹ s⁻¹ whatever the state of division of the platinum, and is of the same order of magnitude as the permeability D_sC_s of oxygen in the adjacent sulfuric acid solution. It is shown, moreover, that the oxygen concentration in the film is very high, about five times that in the solution.     

Platinum nanoparticles decorated Nb2CTx MXene as an efficient dual functional catalyst for hydrogen evolution and oxygen reduction reaction

Here, a dual functional Nb₂CT_x@Pt nanocomposite has been synthesized by in situ reduction method. The Pt loading in the composite has been optimized to get minimum overpotential (141 mV at 10 mA/cm²) for hydrogen evolution reaction (HER) along with a promising Tafel slope of 46.3 mV/dec, while Pt/C shows an overpotential and Tafel slope of 104 mV and 32.4 mV/dec, respectively. The Pt mass activity for Nb₂CT_x@Pt3.8 composite at 100 mV overpotential was 3.44 A g^?1 while the Pt mass activity for conventional Pt/C was 0.7 A g^?1, which shows that the activity of Nb₂CT_x@Pt3.8 composite is approximately 5 times higher than Pt/C. In addition, the catalyst was found to be stable for continuous 500 cycles without any binder molecules. The oxygen reduction reaction (ORR) capability of the material was also evaluated and found that the catalyst exhibited a current density of ?4.28 mA/cm² in the diffusion limiting region in comparison with the current density of ?5.82 mA/cm² for Pt/C at 2600 revolutions per minute (RPM). The Pt mass activity of Nb₂CT_x@Pt3.8 composite for ORR is approximately 10 times higher than Pt/C. The Nb₂CT_x@Pt3.8 composite was able to reduce O₂ completely using the 4-electron pathway with very little peroxide production. From these results, the dual functionality of the Nb₂CT_x@Pt3.8 composite for both HER and ORR has been established.     

Impact of SO2 poisoning of platinum nanoparticles modified glassy carbon electrode on oxygen reduction

An extraordinary recovery characteristic of Pt-nanoparticles from SO₂ poisoning is introduced in this study. Platinum nanoparticles (nano-Pt) modified glassy carbon electrode (nano-Pt/GC) has been compared with polycrystalline platinum (poly-Pt) electrode towards SO₂ poisoning. Two procedures of recovery of the poisoned electrodes were achieved by cycling the potential in the narrow potential range (NPR, 0-0.8 V vs. Ag/AgCl/KCl (sat.)) and wide potential range (WPR, −0.2 to 1.3 V). The extent of recovery was marked using oxygen reduction reaction (ORR) as a probing reaction. SO₂ poisoning of the electrodes changed the mechanism of the oxygen reduction from the direct reduction to water to the stepwise reduction involving the formation of H₂O₂ as an intermediate, as indicated by the rotating ring-disk voltammetry. Using the WPR recovery procedure, it was found that two potential cycles were enough to recover 100% of the activity of the ORR on the nano-Pt/GC electrode. At the poly-Pt electrode, however, four potential cycles of the WPR caused only 79% in the current recovery, while the peak potential of the ORR was 130 mV negatively shifted as compared with the fresh poly-Pt electrode. Interestingly, the NPR procedure at the nano-Pt/GC electrode was even more efficient in the recovery than the WPR procedure at the poly-Pt electrode.     

Enhanced catalytic activity of nanoshell carbon co-doped with boron and nitrogen in the oxygen reduction reaction

The use of carbon cathode catalysts in polymer electrolyte fuel cells instead of the current platinum catalysts is attracting increasing attention. We claim that two factors are important for enhancing the activity of carbon cathode catalysts in the oxygen reduction reaction (ORR): the formation of a nanoshell structure and co-doping with boron and nitrogen. Herein, we investigate the preparation and characterization of active ORR carbon catalysts that combine the above factors. Boron and nitrogen (BN)-doped nanoshell-containing carbon (BN-NSCC) was prepared by carbonizing a mixture of poly(furfuryl alcohol), cobalt phthalocyanine, melamine, and a trifluoroborane–methanol complex at 1000 °C. Transmission electron microscopy and X-ray photoelectron spectroscopy revealed the formation of nanoshell structures with distorted graphitic layers and the introduction of boron and nitrogen atoms, respectively. The ORR activity was evaluated in oxygen-saturated 0.5 mol dm^?3 H₂SO₄ using Koutecky–Levich analysis. The BN-NSCC showed an eight to ten times higher ORR activity than undoped NSCC, with an increased number of electrons participating in the reaction. Tafel analysis revealed a change in the rate-determining step caused by BN-doping. Thus, the combination of a nanoshell structure and co-doping with boron and nitrogen was found to improve the ORR activity of carbon catalysts.     

Electrochemical activity and durability of platinum nanoparticles supported on ordered mesoporous carbons for oxygen reduction reaction

A facile procedure for synthesizing platinum nanoparticles (NPs) studded in ordered mesoporous carbons (Pt–OMCs) based on the organic–organic self-assembly (one-pot) approach is reported. These Pt–OMCs, which can be easily fabricated with controllable Pt loading, were found to possess high surface areas, highly accessible and stable active sites and superior electrocatalytic properties pertinent as cathode catalysts for hydrogen–oxygen fuel cells. The enhanced catalytic activity and durability observed for the Pt–OMC electrocatalysts are attributed to the strengthened interactions between the Pt catalyst and the mesoporous carbon that effectively precludes migration and/or agglomeration of Pt NPs on the carbon support.     

Carbon-coated tungsten oxide nanowires supported Pt nanoparticles for oxygen reduction

Carbon-coated tungsten oxide nanowires were grown directly on carbon fiber of a carbon paper (C–W₁₈O₄₉ NWs/carbon paper) by chemical vapor deposition method and Pt nanoparticles were deposited on the nanowires (Pt/C–W₁₈O₄₉ NWs/carbon paper) to form the composite electrode. The microstructure and electrochemical behavior of the resultant Pt/C–W₁₈O₄₉ NWs/carbon paper composites are characterized by a transmission electron microscope (TEM) and cyclic voltammetry, respectively. The electrocatalytic activities of these composite electrodes for oxygen reduction reaction (ORR) were investigated and higher mass and specific activities in ORR were exhibited as compared to commercial Pt/C electrode.