Papers by Keyword: Electrocatalyst

Abstract: Oxygen evolution reaction (OER) is an essential reaction commonly applied in various energy storage and conversion technologies. One of the common issues of OER lies in its low kinetic activity. Therefore, developing durable, low-cost, and high-performance OER catalysts is critical. Recently, many attempts have used stainless steel mesh (SSM) as the substrate for OER electrodes because SSM is abundant, cheap, and durable. Nickel/iron-based materials, i.e., NiFe₂O₄/NiFe layer double hydroxides (LDHs), are regarded as one of the most excellent OER catalysts in alkaline electrolytes, making them attractive low-cost materials for OER catalysts. However, synthesizing NiFe₂O₄/NiFe LDHs directly on the surface of SSM is challenging. Modifying the SSM surface through cathodization has proved to enhance the adhesion and OER activity. Moreover, the cathodization technique is facile and cost-effective. In this work, the surface of SSM is modified by cathodization treatment. Subsequently, NiFe₂O₄/NiFe LDHs are deposited onto the surface of treated SSM via a low-temperature one-step chemical bath deposition technique. This synthesis is a binder-free method; the resulted electrodes show excellent OER performance without the binder effects. The as-prepared electrodes have a small Tafel slope of 125.4 mV/dec (1 M KOH) and high durability (10 mA/cm2 for 50 hours).

Abstract: In this work, the Cu-alginate/graphene aerogels were prepared by using alginate, graphene and copper chloride as precursors by a freeze-drying process. Finally, N-doped carbon aerogels supported by Cu nanoparticles (NPs) (Cu/N-CAs) were obtained through annealing in the NH₃ atmosphere. The morphology, microstructures, specific surface area, and pore size distribution were studied by SEM, XRD, and BET analysis. The results showed that a significant amount of Cu NPs were uniformly disseminated on the aerogels’ surface, and the catalysts’ specific surface area reached 141 m²/g. Electrochemical tests revealed good catalytic capabilities for the oxygen reduction reaction (ORR) of the as-obtained Cu/N-CAs. Compared to the commercial 20%Pt/C, the Cu/N-CAs exhibited comparable catalytic performance, superior catalytic stability and methanol resistance. The transfer of 3.94 electrons indicated that the Cu/N-CAs were undergoing a four-electron (4e^-) ORR process.

Abstract: CoNi and FeCoNi hydroxide with narrow voltage distance between oxygen reduction reaction and oxygen evolution reaction was synthetized by electro-deposition in low solvent concentration. 5cm² Membrane electrode assemble (MEA) electrolyzers composed with anion exchange membrane, homogenerated catalyst on both cathode and anode gas diffusion layer (GDL) was fabricated for oxygen electrochemical production from air. The current and yield of binary CoNi device reached up to 466.7mA and 4.4mmol/h (94.7% conversion rate) at 1.2V. The ternary FeCoNi device showed only 0.5% degradation from 394.0mA during 12h. The applicability of oxygen production from air by high performance electrochemical devices was demonstrated.

Abstract: A novel electrocatalyst has been developed based on polypyrol-carbon nanofiber (PPy-CNF) support material to increase the stability of Pt/ PPy-CNF/GDL electrocatalyst in direct methanol fuel cell (DMFC). A novel conducting polymer (PPy)-CNF nanocomposites was prepared by a solution dispersion technique and used to support platinum nanoparticles. For preparation of catalyst ink, 20 wt.% Pt/PPy-CNF electrocatalyst with a platinum loading of 0.4 mg cm^-2 was prepared by ethylene glycol (EG) method. Physical and electrochemical properties were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) imaging and cyclic voltammetry (CV) experiments. FTIR results prove the existence of PPy in the support. SEM images showed that the one–dimensional CNFs were efficaciously covered by PPy. The TEM characterization revealed that the fine Pt nanoparticles prepared by polyol method were dispersed on the surface of the electrocatalyst successfully. XRD patterns also revealed that the mean size of Pt crystal nanoparticles was about 3.69, 6.51 and 2.91 nm for Pt/PPy-CNF, Pt/CNF and Pt/C electrocatalyst respectively. The size of the PPy on carbon paper has been measured in the range of 35-40nm by AFM. Based on the electrochemical properties and acceleration tests evaluated by cyclic voltammetry measurements and Chronoamperometric experiments it was found that the as prepared Pt/PPy-CNF/GDL electrode exhibited a comparable electrochemical surface are (ECSA), MOR activity and so stability (in the presence of methanol) with respect to the Pt/CNF /GDL and Pt/C/GDL commercial one. A rather significant reduction in the peak potential of methanol electro-oxidation from 0.69V for Pt/C/GDL to 0.76V for Pt/PPy-CNF/GDL electrode indicates that an increase in the activity for MOR is achieved by replacing the C by PPy-CNF. The corresponding ECSA values for the Pt/PPy-CNF/GDL, Pt/CNF/GDL and Pt/C/GDL electrodes were 108.69, 53.93 and 17.98 m²g^-1 respectively.

Abstract: LaFeO₃ nanoparticles-modified RuO₂ and RuO₂ samples were fabricated by a thermal decomposition and was characterized by powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and cyclic voltammetry tests. XRD results reveal that the RuO₂ and RuO₂-LaFeO₃ samples are mainly a rutile structure. Compared with the RuO₂ sample, the RuO₂-LaFeO₃ sample has smaller crystalline grain size. Cyclic voltammetry analysis shows the voltammetric behaviour and the characteristic potentials of the RuO₂ and the RuO₂-LaFeO₃ samples are similar in 1.0 M KOH solution. Voltammetric charge analysis reveals that the RuO₂-LaFeO₃ sample has higher concentrated of surface active species and larger exposed surface area than the RuO₂ sample. Capacitive measurement results show the Double-layer capacitance (C_dl) and the electrochemical surface area (ECSA) values of the RuO₂-LaFeO₃ sample are approximately 2 times larger than those of the RuO₂ sample, indicating that the electrochemical active surface area increase when integrating of RuO₂ with LaFeO₃ nanoparticles.

Abstract: In response to global energy and environmental issues, development of efficient and robust earth-abundant electrocatalysts for hydrogen evolution reaction is particularly meaningful. In this study, a facile hydrothermal method is developed to synthesize porous CoS₂ nanostructures by using sulfur powder and thiourea as sulfur sources on carbon cloths for highly efficient hydrogen evolution reactions. The huge load of CoS₂ on carbon cloth，their unique porous nanostructures equiped CoS₂ nanomaterials with excellent electrocatalytic properties. The remarkable HER catalytic performance was achieved with -67 mV at a current density -10 mA cm^-2 and the Tafel slope 62 mV dec^-1 in 0.5 M H₂SO₄ solution. The overpotential of HER only lost 2 mV after 1000 cycles with remarkable stability. I think this work opens up a low cost and scalable route to fabricate transition metal-based materials for application in electrocatalysis.

Abstract: The technical issue of direct ethanol fuel cells is slow kinetics of ethanol electrooxidation by using noble metals such as Pt. We propose silica-embedded carbon nanofiber (SECNF) as a catalyst support for the electrooxidation of ethanol to improve catalytic activity of Pt. SECNF was prepared by electrospinning, then Pt nanoparticles were deposited on SECNF. Catalyst characterizations were performed by SEM, EDX, and XRD. Cyclic voltammetry was performed to analyze catalytic activity of Pt/SECNF. The mass activity of Pt/SECNF was 2.9 times higher than a commercially available Pt/carbon catalyst (Pt/C_com). Electrochemically active surface area of Pt/SECNF was lower than Pt/C_com. Hence, the activity enhancement is attributed to the improvement of specific activity for Pt/SECNF. This enhancement is attributed to the interaction between Pt and SiO₂ like hydrogen spillover. Pt/SECNF is a promising catalyst for direct ethanol fuel cells which can reduce Pt loading.

Abstract: The effect of thermal cycling on the agglomeration within 48 hrs of Pt and PtRu electrocatalysts was investigated by using transmission electron microscopy (TEM) and X-ray diffraction (XRD). In comparison with the thermal continuous test, particle agglomeration under the thermal cycle condition was more severe. The PtRu particle size increment was 44.4% and 70.4% for thermal continuous and thermal cycle tests, respectively. These results are in agreement with the direct methanol fuel cells (DMFC) performance test. In the study of the effect of environment, the ethanol solution caused the highest Pt particle agglomeration, followed by methanol and water.

Abstract: Using ammonium metatungstate (AMT), soluble cobalt salt and organic carbon source as the raw materials, the W-Co precursor powder with spherical shell structure was first fabricated by spray conversion method. Then the nanophase WC-Co composite powder was fabricated via calcinations and low temperature reduction-carbonization methods. And the WC powder with the same spherical shell structure was prepared at last by dissolving the Co phase into H₃PO₄ and H₂O₂. The phase composition, powder morphology, chemical components and its distribution of the samples at different stages were characterized by XRD, SEM and EDS. The results confirmed that the powders showing spherical shell structure after spray conversion, calcinations, reduction, carbonization and dissolution. While the amount of surface porosity changed after these treatments. The grain size of WC was about 50nm measured by FWHM of XRD. The electro catalytic activities of the powders towards methanol electro-oxidation were investigated by cyclic voltammetry with a three-electrode system in acidic solution. Compared with the granular WC powder, the electro-catalytic activity of WC-Co composite powder sample decreased, but the electro-catalytic activity of WC powder with spherical shell structure has been significantly improved. These results indicated that the electro catalytic activity of WC can be improved through the formation of spherical shell structure, while the existence and distribution of Co phase could hinder the electro-catalytic activity of WC.

Abstract: This work deals with selected aspects of the formation of intermetallic phases and the occurrence of a synergistic effect in the electrochemical process taking place at such electrode materials. A comparison of the catalytic activity of a variety of metals and intermetallic compounds in the reaction of hydrogen electroevolution and absorption was carried out. It has been found that the catalytic activity of such combinations is much higher than the activity of their individual components and quite often also of precious metals. This paper is also aimed at understanding the electrocatalytic properties of electrodes based on the concept of “activity descriptors”. What is also discussed is the ability of different metals and intermetallic compounds to store hydrogen.