Electrochemical determination of niobium cathode as an efficient electrocatalyst for hydrogen generation in acidic media

Hydrogen gas (H₂) is notified as a renewable energy carrier. It is wanted to discover a low-cost electrocatalyst for the hydrogen evolution reaction (HER) to substitute the high-cost Pt in electrolysis cell. Niobium electrocatalyst nominated to substitute noble materials for electrocatalytic H₂ production and its electrochemical manner was estimated in H₂SO₄ acid of various concentrations utilizing a steady-state polarization and electrochemical impedance spectroscopy (EIS). The influences of acid concentration, cathodic potential and temperature on the H₂ creation were examined. The outcomes display that HER on Nb electrode proceeds by the Volmer-Heyrovsky mechanism. EIS tests, under open circuit and under cathodic polarization, were performed and the fitting has been done utilizing a suggested model for the electrode/electrolyte interface. Apparent activation energies (E_a) were estimated to be ca. 10.5 kJ mol^?1 for the HER on Nb. Thus, Nb is a good electrocatalyst for the cathodic H₂ manufacturing.     

NiMo/Cu-nanosheets/Ni-foam composite as a high performance electrocatalyst for hydrogen evolution over a wide pH range

We designed and fabricated non-precious and highly efficient electrocatalysts of nickelmolybdenum/copper-nanosheets/nickel-foam composites (NiMo/Cu-NS/NF) by step electrodepositions, combining with chemical oxidation method. The catalysts were charaterized by means of SEM, XRD and XPS spectra. Their electrocatalytic activities were assessed by hydrogen evolution reactions (HER) over a wide pH range, where acidic, neutral and alkaline electrolytes were used, respectively. Benefiting from the unique midlayer Cu nanosheets (NS) architecture and optimum Mo–Ni composition at the surface layer which led to high electronic conductivity and large electrochemically active surface area (ECSA), the NiMo/Cu-NS/NF-2 catalyst displayed superior electrocatalytic activities with low overpotentials of η₁₀ = 43, 86 and 89 mV in 0.5 M H₂SO₄, 1.0 M PBS and 1.0 M KOH electrolyte, respectively. Especially in the acidic condition, it exhibited the best electrocatalytic activity with smaller Tafel slope of 54 mV dec^?1 and higher exchange current density of 1.93 mA cm^?2.     

Composition-tunable PtCu porous nanowires as highly active and durable catalyst for oxygen reduction reaction

To accelerate the commercialization of fuel cells, many efforts have been made to develope highly active and durable Pt-based catalyst for oxygen reduction reaction (ORR). Herein, PtCu porous nanowires (PNWs) with controllable composition are synthesized through an ultrasound-assisted galvanic replacement reaction. The porous structure, surface strain, and electronic property of PtCu PNWs are optimized by tuning composition, which can improve activity for ORR. Electrochemical tests reveal that the mass activity of Pt_0.5Cu_0.5 PNWs (Pt/Cu atomic ratio of 1:1) reaches 0.80 A mg_Pt^?1, which is about 5 times higher than that of the commercial Pt/C catalyst. Notably, the improved activity of the porous nanowire catalyst is also confirmed in the single-cell test. In addition, the large contact area with the carrier and internal interconnection structure of Pt_0.5Cu_0.5 PNWs enables them to exhibit much better durability than the commercial Pt/C catalyst and Pt_0.5Cu_0.5 nanotubes in accelerated durability test.     

Magnetic field enhancement of electrochemical hydrogen evolution reaction probed by magneto-optics

External magnetic fields affect various electrochemical processes and can be used to enhance the efficiency of the electrochemical water splitting reaction. However, the driving forces behind this effect are poorly understood due to the analytical challenges of the available interface-sensitive techniques. Here, we present a set-up based on magneto- and electro-optical probing, which allows to juxtapose the magnetic properties of the electrode with the electrochemical current densities in situ at various applied potentials and magnetic fields. On the example of an archetypal hydrogen evolution catalyst, Pt (in a form of Co/Pt superlattice), we provide evidence that a magnetic field acts on the electrochemical double layer affecting the local concentration gradient of hydroxide ions, which simultaneously affects the magneto-optical and magnetocurrent response.     

Graphene-based electrocatalysts: Hydrogen evolution reactions and overall water splitting

Recently, carbon-based materials (e.g., graphene, carbon nanotubes, carbon quantum dots) have been used as electrocatalysts to catalyze the reactions such as hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). Among them, graphene has attracted attention as an electrocatalyst, and its electrocatalytic performances have been improved by doping with metals and non-metals, surface and defect engineering, and hybrid development. In this perspective, the present paper reviewed the recent advances (2018 onwards) on the progress of graphene-based electrocatalysts for HER and overall water splitting (OWS). It is emphasizing strategies for optimizing electrocatalytic properties followed by challenges and future outlook. This review will provide the essential ideas and strategies that can help design graphene-based electrocatalysts of high performance that can be implemented for sustainable energy application.     

Facile in-situ deposition of Pt nanoparticles on nano-pore stainless steel composite electrodes for high active hydrogen evolution reaction

Hydrogen is regarded as a clean and highly efficient renewable energy. The platinum catalytic electrode is widely used in hydrogen evolution reaction (HER), but it has affected its commercial application because of its high cost. Therefore, the study on cost-effective and high-active catalysts toward HER is required to realise large-scale hydrogen production. In this work, we present a novel Pt/NPSSF catalyst prepared by a one-step in-situ deposition of Pt precursor on a nano-porous stainless-steel film (NPSSF) substrate. The prepared catalyst was evaluated in acidic and alkaline conditions for its HER activities. The preliminary results demonstrate that the Pt/NPSSF electrodes have superior catalytic activity for HER. The hydrogen overpotential of Pt/NPSSF is ?70mV (RHE) in the alkaline solution, which is lower than the Pt electrode of ?184mV. At the same time, we also obtained ?71.2 mV of overpotential for the Pt/NPSSF electrode, which is similar to the ?73mV of Pt electrode in the acid solution. The Tafel graphs plotted from the LSV curves indicate the different HER mechanism in the alkaline and acid solution. The HER kinetics of the Pt/NPSSF were studied using EIS. Comparing Pt/NPSSF to Pt electrode, the multi-pore structures of NPSSF and the Pt nanoparticles active sites decrease the charge transfer-resistance for the HER process. The facile preparation, high efficiency and low value of the Pt/NPSSF composite electrodes demonstrate the promising applications in HER.     

Indoor heterogeneous photochemistry of furfural drives emissions of nitrous acid

People spend approximately 80% of their time indoor, making the understanding of the indoor chemistry an important task for safety. The high surface-area-to-volume ratio characteristic of indoor environments leads the semi-volatile organic compounds (sVOCs) to deposit on the surfaces. Using a long path absorption photometer (LOPAP), this work investigates the formation of nitrous acid (HONO) through the photochemistry of adsorbed nitrate anions and its enhancement by the presence of furfural. Using a high-resolution proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS), this work also investigates the surface emissions of VOCs from irradiated films of furfural and a mix of furfural and nitrate anions. Among the emitted VOCs, 2(5H)-furanone/2-Butenedial was observed at high concentrations, leading to maleic anhydride formation after UV irradiation. Moreover, the addition of potassium nitrate to the film formed NO_x and HONO concentrations up to 10 ppb, which scales to ca. 4 ppb for realistic indoor conditions. This work helps to understand the high levels of HONO and NO_x measured indoors.     

Structure development and dielectric properties of Zn-doped Pb([Mg,Fe],W)O3 perovskite ceramics

Ceramic samples of a pseudo-binary system Pb(Mg_1/2W_1/2)O₃-Pb(Fe_2/3W_1/3)O₃ (PMW-PFW) were prepared by solid-state reaction. In addition, their compositions were modified by 20 mol% Pb(Zn_1/2W_1/2)O₃ (PZW) doping in order to investigate the role of zinc in the perovskite formation and dielectric properties. The perovskite contents were ≥95.1% at the overall composition range, except for a significantly low value of 79.0% at 0.8PFW-0.2PZW. The extension of sintering time for PMW accelerated superstructure formation, resulting in the ordering factor increased up to 0.40 after 12 hours heat treatment. The maximum dielectric constant values increased with increasing PFW fractions. In comparison, the phase transition temperatures decreased sharply (by up to 161°C) at low concentrations of PFW, followed by mild changes (by up to 47°C) afterward. The dielectric constant spectra were analyzed in terms of diffuseness characteristics, which reflected the phase transition modes quite well.     

多氢酸酸化反应特征及动力学

利用自制多氢酸液XS-1进行静态岩粉溶蚀与岩心流动实验,通过SEM、ICP等实验考察了多氢酸的缓速性与预防二次沉淀性能,并研究了多氢酸与岩心反应动力学特性。结果表明,XS-1多氢酸液具有良好的缓速与预防二次沉淀性能,反应后残酸的极限浓度为0.296 1 mol/L,酸液有效作用时间为6~7 h。在该多氢酸体系下岩心渗透率提高至4.15倍,在此条件下以酸岩反应动力学参数模型建立动力学方程,反应速率比同条件下普通酸液小,进一步证明多氢酸具有一定的缓速性。