Electrocatalysis of chlorine evolution on different materials and its influence on the performance of an electrochemical reactor for indirect oxidation of pollutants

Two different Ti/Pt–Ir materials (commercial and home made) and Ti/PdO + Co₃O₄ were investigated for their electrocatalytic properties versus Cl₂ evolution reaction. The materials were used in a batch electrochemical reactor to treat biologically recalcitrant di-azo compound. An electrochemically driven oxidation, mediated by a Cl₂/Cl⁻ couple, proved efficient for destruction of this complex organic molecule, causing cleavage of the conjugated double bonds and destruction of unsatured bonds. Both Ti/Pt–Ir materials performed well; lower kinetics obtained with the Ti/PdO + Co₃O₄ anode was caused by adsorption of the model compound, evidenced in preliminary voltammetric measurements. The dye oxidation reaction followed the second order kinetics with partial orders in the model compound and (time varying) chlorine concentrations equal to one. Specific energy consumption of 3.12 kWh m⁻³ proved the process more economic than the homogeneous phase oxidation.     

隔膜电解制备Mn^3＋的研究

对电解媒质ＭｎＳＯ４在有隔膜条件下电解制备Ｍｎ３＋过程进行了研究。结果表明，无论均相还是非均相隔膜电解，在常温２０℃、４０％Ｈ２ＳＯ４介质中，当电流密度、ＭｎＳＯ４浓度、电解时间在很宽的范围变动时，电流效率保持很高，至少在８５％以上。     

Preparation and characterization of a PtRu/C nanocatalyst for direct methanol fuel cells

PtRu/C nanocatalysts were prepared by changing the molar ratio of citric acid to platinum and ruthenium metal salts (CA:PtRu) from 1:1, 2:1, 3:1 to 4:1 using sodium borohydride as a reducing agent. Transmission electron microscopy analysis indicated that well-dispersed smaller PtRu particles (2.6 nm) were obtained when the molar ratio was maintained at 1:1. X-ray diffraction analysis confirmed the formation of PtRu alloy; the atomic percentage of the alloy analyzed by the energy dispersive X-ray spectrum indicated an enrichment of Pt in the nanocatalyst. X-ray photoelectron spectroscopy measurements revealed that 83.34% of Pt and 79.54% of Ru were present in their metallic states. Both the linear sweep voltammetry and chronoamperometric results demonstrated that the 1:1 molar ratio catalyst exhibited a higher methanol oxidation current and a lower poisoning rate among all the other molar ratios catalysts. The CO stripping voltammetry studies showed that the E-TEK catalyst had a relatively higher CO oxidation current than did the 1:1 molar ratio catalyst. Testing of the PtRu/C catalysts at the anode of a direct methanol fuel cell (DMFC) indicated that the in-house PtRu/C nanocatalyst gave a slightly higher performance than did the E-TEK catalyst.     

Electro-oxidation of hydrazine on electrodes modified with vitamin B12

In this paper we report a kinetic study of the electro-oxidation of hydrazine catalyzed by vitamin B₁₂ pre-adsorbed on an ordinary pyrolytic graphite electrode. Kinetic parameters were determined by linear sweep voltammetry and rotating-disk electrode polarization curves. The order of the reaction is 1 in OH⁻ ions and Tafel plots give slopes of 80 mV/decade. A possible redox-catalysis mechanistic scheme is proposed.     

Controllable electrodeposition synthesis of Pd/TMxOy-rGO/CFP composite electrode for highly efficient methanol electro-oxidation

A novel and high-efficiency Pd/TM_xO_y-rGO/CFP (TM_xO_y = Co₃O₄, Mn₃O₄, Ni(OH)₂) electrocatalyst for directly integrated membrane electrode was synthesized by controllable cyclic voltammetry electrodeposition combined with hydrothermal process. The results showed excellent performance towards methanol oxidation reduction. The Pd/Co₃O₄-rGO/CFP as-prepared catalyst has the best electrocatalytic activity, and mass activity is 5181 mA·mg⁻¹_Pd, which is about 40 times and 4.3 times that of the commercial Pd/C and Pt/C catalyst (JM). It can be attributed that the small size of Pd nanoparticle, uniformity of distribution, and the synergistic interaction between transition metal oxide on the support surface and Pd nanoparticles. The prepared Pd/TM_xO_y-rGO/CFP composite electrode is a promising catalyst for integrated membrane electrode assembly of proton exchange membrane fuel cells in the future.     

Catalytic enhancement of formic acid electro-oxidation through surface modifications with gold on supported Pt nanoparticles

The Formic Acid Electro-oxidation (FAEO) on Pt/Au Nanoparticles (PtAu NP) supported on Hierarchical Porous Carbon (HPC), was studied by cyclic voltammetry and chronoamperometry. The supported HPC-Pt nanoparticles were surface modified by Au spontaneous deposits. The morphological and compositional characterization was performed by Scanning Electron Microscopy (SEM) coupled with Electron Dispersive Spectroscopy (EDS). A significant increase of the current densities for FAEO in the potential region 0.1–0.75 V_RHE was observed on HPC-PtAu catalysts. The comparison with HPC-Pt electrodes results show that Au atoms presence on Pt nanoparticles is a key factor to improve the catalysts performance. Based on our results, a clear change in FAEO mechanism on HPC-PtAu catalysts with respect to HPC-Pt was evidenced.     

Improved electrocatalytic kinetics of nickel hydroxide nanoparticles on Vulcan XC-72R carbon black towards alkaline urea oxidation reaction

Nickel hydroxide nanoparticles were fabricated on Vulcan XC-72R carbon black using various reducing agents through assisted microwave polyol process. The formed electrocatalysts using sodium borohydride [Ni(OH)₂/C–NB], ethylene glycol [Ni(OH)₂/C–EG] and a mixture of them [Ni(OH)₂/C–EGNB] displayed an electrocatalytic activity towards urea oxidation in NaOH solution. The oxidation peak potential and current density values were greatly influenced by the employed reducing agent. Lower onset and peak potential values were measured at Ni(OH)₂/C–EGNB, while Ni(OH)₂/C–EG exhibited the highest oxidation current density during urea oxidation reaction. Electroactive surface area measurements revealed that the number of available active sites for the oxidation reaction was arranged in an ascending order as Ni(OH)₂/C–NB < Ni(OH)₂/C–EGNB < Ni(OH)₂/C–EG. The diffusion coefficient of urea molecules at Ni(OH)₂/C–EG and Ni(OH)₂/C–EGNB was 14.69 and 5.90 times higher than that at Ni(OH)₂/C–NB. Stable performance was measured at all studied electrocatalysts over prolonged operation suggesting their valuable application as efficient anode materials in direct urea oxidation fuel cells.     

Enhanced electrocatalytic performance of Pt nanoparticles immobilized on novel electrospun PVA@Ni/NiO/Cu complex bio-nanofiber/chitosan based on Calotropis procera plant for methanol electro-oxidation

Bioinspired Ni/NiO nanocomposite was synthesized in the Calotropis procera wood and its size and structure were confirmed by transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). The green and environmental friendly approach was performed for the preparation of copper nanocomplex (CC) under ultrasonic irradiation. Polyvinyl alcohol (PVA) nano-biofibers containing Ni/NiO nanocomposite and copper nanocomplex were obtained by electrospinning method. This novel bio nanocomposite was characterized by field-emission scanning electron microscope (FESEM), TEM, and atomic force microscopy (AFM) for further investigation. Novel Pt/PVA@Ni/NiO/Cu nanocomplex/chitosan (Pt/PVA@NOCC/CH) was synthesized and its catalytic performance was studied towards methanol electro-oxidation. Pt/PVA@NOCC/CH catalyst exhibits enhanced electrocatalytic performance towards methanol oxidation (MO), compared to Pt/PVA/CH and Pt/PVA@NOCC with respect to its better stability, larger electrochemically active surface area, enhanced mass activity, and improved resistance to poisoning. By and large, Pt/PVA@NOCC/CH is known as a promising electrocatalyst for fuel cells.     

Nickel-decorated MoS2/MXene nanosheets composites for electrocatalytic oxidation of methanol

Nickel incorporated on MoS₂/MXene composites (NiMoS₂/MXene) via a wet impregnation method is used as an anode electrode material for methanol electro-oxidation. X-ray diffraction, X-ray photoelectron spectra, and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy techniques were used for the confirmation of MoS₂/MXene formation. Textural properties of catalysts were obtained in N₂ adsorption-desorption analysis. Electrochemical measurements in 0.1 M KOH demonstrated the better electrocatalytic activity of NiMoS₂/MXene catalysts. The NiMoS₂/MXene system exhibited enhanced electrocatalytic activity for methanol oxidation due to low onset potential offered by Ni, high tolerance toward CO poisoning by MoS₂, and high conductivity and high mechanical stability of MXene. NiMoS₂-3/MXene catalysts exhibited high current density, electrochemical active surface area, long-term stability, and low Rct value. Based on the electrochemical results, NiMoS₂/MXene catalysts is a highly electroactive anode material. Hence can be utilized in fuel cell applications such as Direct Methanol Fuel Cell (DMFC).     

Porous Ni2P nanoflower supported on nickel foam as an efficient three-dimensional electrode for urea electro-oxidation in alkaline medium

Porous Ni₂P nanoflower supported on nickel foam (Ni₂P@Ni foam) electrodes are synthesized via a simple hydrothermal growth strategy accompanied with further phosphating treatment. The prepared electrodes are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). Electro-catalytic performances towards urea electro-oxidation are tested by cyclic voltammetry (CV), chronoamperometry (CA) coupled with electrochemical impedance spectroscopy (EIS). By phosphating Ni(OH)₂ precursor, the final obtained Ni₂P@Ni foam electrode presents a porous Ni₂P nanoflower structure within abundant porosity, and so exposes a large amount of electro-catalytic active sites and electronic transmission channels to accelerate the interfacial reaction. Compared with Ni(OH)₂@Ni foam precursor, the Ni₂P@Ni foam catalyst exhibits more excellent electro-catalytic activity as well as lower onset oxidation potential. Remarkably, the Ni₂P@Ni foam catalyst reaches a peak current density of 750 mA cm^?2 with an onset oxidation potential of 0.24 V (vs. Ag/AgCl) accompanied by an excellent stability in 0.60 M urea with 5.00 M KOH solutions. Benefiting from the unique porous nanosheet structure, the as-synthesized Ni₂P@Ni foam catalyst performs a highly enhanced catalytic behavior for alkaline urea electro-oxidation, indicating that the material can be hopefully applied in direct urea fuel cells.