Non-noble Electrodes Research Articles

Co-deposition of Ni-Mo alloy film catalysts for hydrogen evolution from an ethylene glycol system.

Owing to the depletion of renewable energy sources, manufacturing stable, efficient and economical non-noble electrode materials for the hydrogen evolution reaction (HER) through electrochemical water splitting is a promising avenue. In this work, Ni-Mo alloy films containing different Mo concentrations were synthesized via potentiostatic technique, and the mechanism of Ni2+ and Mo6+ co-deposition in an ethylene glycol system (EG) was recorded. The co-deposition mechanism of Mo6+ and Ni2+ in the EG shows that the existence of Ni2+ can facilitate the reduction of Mo6+, while Mo6+ can impede the reduction of Ni2+. Furthermore, both functions could be reinforced owing to the improved content of Ni2+ and Mo6+ in the EG system. Ni-Mo alloy films containing different Mo concentrations could be obtained from the EG solution, and their microstructures could be changed by changing the Mo content. Scanning electron microscopy micrographs exhibit that Ni-Mo alloy films with 10.84 wt% Mo show a cauliflower-like pattern. Benefiting from the alloying technique to modify the Ni electronic structure with Mo, coupled with the concurrent presence of an appropriate cauliflower-like structure, Ni-Mo alloy films with 10.84 wt% Mo show remarkable catalytic activity and durability with an HER overpotential of 74 mV (η 10, overpotential was recorded at j = 10 mA cm-2) in 1.0 M KOH solution.

Modulating interfacial charge distribution of NiSe nanoarrays with NiFe-LDH nanosheets for boosting oxygen evolution reaction

Developing efficient, robust non-noble electrodes for the water oxidation in electrocatalytic water splitting is challenging because the physicochemical properties of the electrocatalysts can extremely affect their OER catalytic activity. The interface engineering of materials is promising for modulating the surface properties of catalysts. Herein, vertically aligned NiSe nanoarrays were prepared in situ using a facile solvothermal selenization technique. NiSe@NiFe-LDH nanointerfaces were produced by electrodeposition. The remarkable OER electrocatalytic performance of NiSe@NiFe-LDH heterojunction was evidenced by the overpotentials for driving 100 and 500 mA cm−2, which are only 232 and 302 mV, respectively. Theoretical arithmetic and experimental tests revealed that the prepared electrode possessed high OER catalytic activity, may be ascribed to charge redistribution between the interfaces of NiSe and NiFe-LDH. The theoretical calculation showed that the generated electron transfer enable the electronic structure to be sufficiently modulated, which perfected the binding energy of the *OOH intermediates, issuing in a reduction of the reaction obstacle of the rate-determining procedure, and improved the OER activity consequently. This work proposes an effective and promising solution to fabricate non-precious metal-based heterostructure materials with excellent catalytic properties for energy storage and transduction.

Hydrogen evolution reaction in acidic and basic medium on robust cobalt sulphide electrocatalyst

Huge research interest has been paid to produce the robust, efficient and large area electrodes based on non-noble electrocatalyst as an alternative of Pt. Herein, we report the facile synthesis of cobalt sulphide (CoS) based electrocatalyst with polycrystalline structure and non-uniform morphology. Also, flexible, robust, large area and bio-degradable electrodes on paper are prepared. Owing to different metal electronic states like Co2+ and Co3+, CoS electrocatalyst show rapid hydrogen evolution reaction. CoS based electrodes shows HER activity with overpotential of 284 mV in alkaline medium and 198 mV in acidic medium. In alkaline medium, electrodes follow sluggish Volmer reaction while in acidic, dynamic Heyrovsky-Volmer reaction is step determining reaction step. Paper based electrodes functionalised by CoS electrocatalyst advocate the futuristic development of non-noble electrodes for clean energy generation via electrocatalytic HER.

Selective electrocatalytic reduction of nitrate to dinitrogen by Cu2O nanowires with mixed oxidation-state

• CuO/Cu 2 O NWs contains switchable oxidation states of Cu (I/II to 0/I). • N 2 selectivity is 99.8% over Cu/Cu 2 O NWs, the highest reported so far. • Cu/Cu 2 O NWs provides active sites for hydrogen/oxygen-adsorbing simultaneously. • Cu/Cu 2 O NWs yields sufficient H* and limit hydrogen bubbles negative effect. • N 2 production based on NO 3 RR is proceeded by H*-mediated route. Selective electrocatalytic nitrate reduction reaction to dinitrogen is a promising water treatment technology to manage nitrate. While, a lack of efficient electrode remains the primary hurdle for achieving the goal. For non-noble electrode, the strong adsorption of oxygen atoms on Cu resulted in low selectivity and inducing nitrite accumulation during the long-term operation. Herein, it is found that Cu 2 O nanowires with mixed oxidation-state can selective reduction of nitrate to dinitrogen. CuO-coated Cu 2 O nanowires (CuO/Cu 2 O NWs) was electrochemically converted into Cu/Cu 2 O NWs for hydrogen/oxygen-adsorbing which was verified by In-situ infrared spectro-electrochemical experiments. H 2 split and H*-adsorbing of Cu/Cu 2 O are desired to yield sufficient H* and limit hydrogen bubbles negative effect. Online differential electrochemical mass spectrometry confirmed dinitrogen generation over Cu/Cu 2 O NWs with over 99.8% selectivity. Computational studies suggest that active Cu/Cu 2 O NWs reduces the free energy changes associated with both nitrate activation and N − N coupling. Energetically favorable pathways for dinitrogen production based on nitrate reduction are proposed herein and the origin of this selective dinitrogen formation is clarified.

Highly Active Binder Free Plasma Sprayed Non-Noble Metal Electrodes for Anion Exchange Membrane Electrolysis at Different Reduced KOH Concentrations

The production of hydrogen by the water electrolysis technique to provide a fossil fuel alternative energy source has attracted a plethora of attention among the other different methods in the context of sustainability, renewable energy source utilization and green technology.[1] Conventional alkaline water electrolyzer (AWE) offers many advantages compared with other systems. One of the major advantages of AWE over proton exchange membrane water electrolyser (PEMWE) is the replacement of conventional noble metal electrocatalysts with active, stable and relatively low-cost transition metal catalysts. However, AWE electrolyzers suffer from lower operational current density compared with their PEMWE counterpart. Like AWE, anion exchange membrane (AEM) electrolyzer does not require noble metal catalysts, which makes this technology much less expensive than PEMWE, while possessing the advantage of PEMWE. However, the electrochemical water splitting performance of AEM water electrolysis is still much lower than that of PEMWE. Focusing on this issue, the presented work aims at improving the performance of AWE and AEM electrolysers by developing cost effective non-noble electrodes on macro-porous transport layer (MPL) using the air plasma spray deposition method.[2] MPLs were fabricated by depositing Ni-graphite on porous substrates. Graphite was removed during particle in-flight forming a controlled porous layer. Electrodes were developed by plasma spraying of NiMoAl for cathode and NiAl for anode on top of the MPL followed by activation in which Al was partially leached out from layers of both electrodes using an alkaline solution. Electrochemical tests were conducted on half-cell in 6M KOH solution and then in the full cells for AWE and AEM in 6M and 0.3M KOH, respectively. The electrochemical performance is recorded via over-potential measurements, electrochemical impedance spectroscopy (EIS), cyclic voltammetery and polarization curve. With optimal combination of MPL and electrodes, current density of 0.5 Acm-2 at 1.80 V was recorded as the initial performance in 6M solutions for AWE using Zirfon separator and the current density of 0.31 Acm-2 at 1.80 V was recorded for AEM electrolyzer with more dilute KOH solution (0.3M) using an anion exchange membrane. 64 days of abusive testing was conducted for the AWE without measurable degradation in the performance in 6M KOH. The catalysts developed in this work will be promising in supporting the pursuit of cheap, affordable and ideal eco-friendly hydrogen fuel. [1] F. Razmjooei, K.P. Singh, D.S. Yang, et al., Acs Catalysis, 2017, 7, 2381-2391. [2] A.S. Gago, S.A. Ansar, B. Saruhan, et al., J Power Sources, 2016, 307, 815-825.

Preparation of Mo2C–carbon nanomaterials for hydrogen evolution reaction

Highly active, stable and low-cost noble metal-free electrocatalysts are essential for production of hydrogen. However, preparation of such catalysts is still highly challenging so far. In this work, the Mo2C–carbon nanomaterials have been prepared by controlled thermal technique. By controlling concentration of the reactants in the experimental condition, the Mo2C–carbon nanomaterials have been fabricated, which leads to decreases in contact resistance b/w Mo2C–carbon nanomaterials and graphitic carbon atoms. As a result, the Mo2C–carbon nanomaterial electrode shows remarkable activity for hydrogen evolution reactions with a small onset overpotential of 95 mV, a Tafel slope of 62 mV dec−1, an high exchange current density of 0.32 mA cm−2, good stability during long-term 1000 cycles and exhibits long-term durability for several days. This study opens a new method for the preparation of highly active non-noble electrode for production of hydrogen from water splitting.

Continuous electrochemical oxidation of biomass derived 5-(hydroxymethyl)furfural into 2,5-furandicarboxylic acid

A continuous electrochemical process with integrated product separation has been developed for production of 2,5-furandicarboxylic acid (FDCA) by oxidation of 5-(hydroxymethyl)furfural (HMF) in aqueous alkaline media on non-noble Ni/NiOOH foam electrodes at ambient conditions. Initially, voltammetry studies were performed in both, acid and alkaline media, on various catalyst materials: Au, Au3Pd2, Pt, PbO2, Ni/NiOOH and graphite. Preparative electrolysis was performed on Au, Au3Pd2, Pt, PbO2, Ni/NiOOH electrodes in a divided glass cell and Ni/NiOOH showed the best performance with an FDCA yield of ≈ 90% and a Faradaic efficiency of ≈ 80%. The electrolysis conditions were then optimized to industrially relevant conditions in a filter-press type flow reactor with Ni/NiOOH foam anode. HMF concentrations as high as 10 wt% were converted to FDCA at pH 12 in a buffer free 0.1 M Na2SO4 electrolyte with continuous addition of NaOH to maintain constant pH. An FDCA separation yield up to 95% was achieved via pH shift crystallization. The electrolysis and FDCA separation results were used for the design and construction of a bench-scale system where continuous FDCA production, including integrated product separation, was tested and reported in this work. This publication for the first time presents a continuous electrochemical FDCA production system with integrated product separation at industrially relevant product concentrations, 10 wt% HMF, and utilizing non-noble electrode materials.

TNT detection using a voltammetric electronic tongue based on neural networks

We report here the use of a voltammetric electronic tongue based on simple metallic electrodes for the detection and discrimination of different concentrations of 2,4,6-trinitrotoluene (TNT) in acetonitrile:water 1:1 (v/v) mixtures. The tongue consisted of noble working electrodes made of iridium, rhodium, platinum and gold and non-noble electrodes including silver, copper, cobalt and nickel. Both the self-organizing map (SOM) and multi-layer feed-forward network (MLFN) neural networks were applied to the data obtained from the electronic tongue and TNT solutions. From SOM analysis it was established that a suitable response in terms of a correct classification of the TNT concentration was observed when using only noble metal electrodes and only 5 selected pulses. Similar good classifications were found when using MLFN. Moreover, the algorithm of neural network MLFN was embedded in a microcontroller in order to obtain a smart portable system for discrimination of TNT. In this case an R2 of 0.993 was obtained for predicted vs observed graphs of concentrations of TNT concentrations.

Accurate concentration determination of anions nitrate, nitrite and chloride in minced meat using a voltammetric electronic tongue

A method for predicting levels of chloride, nitrite and nitrate in minced meat by using an electronic tongue based on pulse voltammetry is proposed here. The electronic tongue consists of a set of noble (Au, Pt, Rh, Ir, Ag) and non-noble (Ni, Co, Cu) electrodes that were housed inside a stainless steel cylinder used at the same time as both the body of the electronic tongue system and the counter/reference electrode. An electrochemical study of the response of the anions Cl −, NO 3 − and NO 2 − using the different noble and non-noble electrodes was carried out in water in order to design a set of pulses for the electronic tongue. The determination of the concentration of chloride, nitrate and nitrite with the voltammetric tongue was carried out on both saline solutions (brines) and minced meat. The addition of the salts was performed following an experimental design in which a system of three compounds/three levels was established. Multivariate analysis including cross validation and partial least square (PLS) techniques were applied for data management and prediction models building. A very good prediction of the concentration of the anions chloride, nitrate and nitrite was achieved in brines. In minced meat, PLS models showed reduction in the prediction capabilities caused by a matrix effect, nevertheless the system still shows good accuracy and precision in the determination of concentration levels of these anions.

Investigation of Electrode Materials as Sensors in a Voltammetric Electronic Tongue

In this work different electrode materials were investigated as sensors in a voltammetric electronic tongue. Basically, the electronic tongue is based on the combination of nonspecific sensors (electrodes) and pattern recognition tools, for example principal component analysis (PCA). Copper, glassy carbon, nickel, palladium, silver, tin, titanium and zirconium together with more traditional electrode materials such as gold, iridium, and platinum were studied. Cyclic voltammetry was applied to study typical model reactions in solutions containing different electroactive compounds, like ascorbic acid, glucose, histidine and potassium hexacyanoferrate(II). Different sensitivity and selectivity were obtained with the electrodes. Large responses were for example found for the amino acid and the carbohydrate using the copper, nickel and silver electrode. Some of the electrodes were employed in multicomponent solutions, i.e., liquid washing detergents from different suppliers together with differential pulse voltammetry. Responses from the electrodes in combination with PCA showed that they separated the detergents to different extents. This was further used when information from the sensors was merged together for successful discrimination of the detergents. It was found that two detergents close to each other in the score plot were from the same supplier. Furthermore, scanning electron microscopy (SEM) was used to monitor surface changes at the nonnoble electrodes (copper, nickel, and silver).

Zirconia-based SOFC with non-noble electrodes fed by air–methane mixture

One- and two-chamber solid oxide fuel cells (SOFCs) fed by an air–methane mixture (AMM) were studied at 550–700°C. (Y 2O 3) 0.04(Sc 2O 3) 0.06(ZrO 2) 0.9 was used as a solid electrolyte, ceria-doped Ni-YSZ-cermet (CNC) and SrO-doped LaMnO 3 (LSM) were used as electrodes. In the experiments with the two-chamber cell, it was stated that the LSM-electrode did not catalyse methane partial oxidation and its potential was close to the potential of free oxygen mixed with methane and nitrogen. The CNC-electrode was a good catalyst for methane partial oxidation and its potential was close to the potential of the mixture formed in methane partial oxidation process. In the one-chamber cell, the current density was about 15 mA/cm 2 at the terminal voltage 500 mV within an interval of 550–650°C.

Electrocatalytic oxidation of saccharose in alkaline medium

The electrocatalytic oxidation of saccharose solutions was carried out in alkaline medium on various noble and non-noble electrodes, with the aim of checking the electroreactivity of saccharose and its potentiality as a raw material for electrosynthesis. The best electrocatalytic activity was obtained with gold. In this latter case, chromatographic analysis of electrolysed solutions allowed us to identify numerous monocarboxylic acids, some of them resulting from the breaking of the COC bond.