RDE Method Research Articles

(Invited) PGM-Free Oer and HER Electrocatalysts for Alkaline Electrolyzers

Introduction Fuel cell technology has been extensively developed in order to create new clean sources of energy. In order to have a wide implementation of fuel cell devices powered by hydrogen (H2), an inexpensive source of clean H2should be created. One of the technologies that produces hydrogen gas is the splitting of water through electrolysis. The majority of electrolyzers available on the market use proton exchange membrane (PEM) technology, which requires catalysts consisting of expensive and rare platinum group metals (PGMs) due to its acid chemistry. To increase penetration into the water electrolyzer and fuel cell markets, abundant and inexpensive materials should be incorporated. Alkaline exchange membrane water electrolysis (AEMWE) is an alternative technology that does not require PGM catalysts and, therefore, enables the use of base metals, alloys and oxides. The goal of this research has been focused on the creation of a catalyst that is stable in alkaline media, has a high surface area, is easy to synthesize, and can be produced at a lower cost while maintaining a high oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity. Experimental Unsupported OER ternary Ni-Mo-Co materials were synthesized by the Sacrificial Support Method (SSM) using a high surface area silica [1-5]. The following process was followed, and produced a NiMoCo OER catalyst achieving a surface area (SA) of 25 m2 g-1. 15g of EH-5 (SA=400 m2 g-1) silica, 2.5g of nickel nitrate, 2.5g of copper nitrate and 3g of ammonium molybdate tetrahydrate were mixed by grinding them in a porcelain crucible. The crucible was placed into a tube furnace and heated to 100 °C with a ramp rate of 10ºC/min. The 100°C temperature was held for 50 minutes before an additional temperature ramp was conducted at an interval of 5ºC/min until 550°C was reached and held for four hours. During this time, a reducing atmosphere was maintained using 7% H2. The silica was later removed by rinsing with 7M potassium hydroxide (KOH) for 24 hours, followed by washing and drying. HER catalysts were based on Ni-M materials (M=Mo and W) supported on high surface area carbon with loading of 50wt%. Precursors of transition metals were deposited by wet impregnation on surface of KetjenBlack 600 followed by water evaporation. Powder was reduced in 7% H2at T=550°C and t=1h. After slow passivation materials were used for HER. Characterization. The catalysts were characterized by BET, SEM, TEM and XRD methods, and catalytic activity for ORR and OER were measured in alkaline media using the RDE method. Pt wire was used as the counter electrode, and the reference electrode was a Hg/HgO corresponding to an RHE of 0.926 at 25°C. Cell testing was performed using a Fuel Cell Technologies 25 cm2fuel cell stack, modified for electrolysis operation. Results and Discussion SEM images of NiMo/KB show that catalysts particles have a similar size with carbon particle on the range of ~20-40nm, which is expected for such a high loading (Figure 1, top left). The surface area was measured at 450±10 m2 g-1 via BET analysis.Electrochemical activity of the OER is shown in Figure 1 (top right). Operational testing was conducted on the NiMoCo OER catalyst provided by UNM in the 25 cm2 cell previously described. As shown below in Figure 1 (bottom), the UNM supplied material experienced relative stability at the steady-state current density of 200 mA/cm2, as compared to the PGM based reference plot. Both tests used the same membrane and electrode binders.

MgO-Templated Mesoporous Carbon As a Catalyst Support for Polymer Electrolyte Fuel Cells

Catalyst poisoning by specific adsorption of the sulfonic acid anion of ionomers has been known as one of the main performance-limiting factors of PEFCs. In a recent study, it was reported that the catalyst poisoning can be suppressed by using a mesoporous carbon (mesoporous carbon nano-dendrites) as a cathode catalyst support [1]. Here, we present that a similar effect can be obtained by using a MgO-templated mesoporous carbon [2] having meso-pores the sizes of which are more-systematically controllable by changing the size of the MgO templates than for conventional carbon supports. An MgO-templated carbon denoted as CNovel® was purchased from Toyo Tanso Inc. The mean diameter of its mesopores is ca. 5 nm (the template MgO size was 5 nm). The sample was graphitized by a heat treatment at 2,100 °C for improving the chemical stability under electrochemical conditions and was crushed by a bead mill to form secondary particles smaller than hundreds nm in size. The obtained powder was immersed in 1 M HNO3 at 80 °C for 1 h to introduce hydrophilic surface groups for facilitating Pt deposition. After thoroughly washing it with pure water, platinum nanoparticles were deposited in aqueous media by using hexahydroxy-platinate as a platinum source. The ORR activity of the prepared catalyst was evaluated by the thin-film RDE method (without ionomers) in aqueous media (0.1 M HClO4) and in MEAs prepared with a Nafion® ionomer (I/C=1.0). The results were compared those of Pt/Vulcan. Figures 1a and 1b show that TEM images of the catalysts. Platinum particles of ca. 2 nm are observed on both the carbons. While Pt/Vulcan shows platinum particles only on the outer edge of the carbon particle, Pt/CNovel shows platinum particles not only on the outer edge but also on the mesopores inside the carbon particle. Figure 1c shows the I-V curves of MEAs using Pt/CNovel and Pt/Vulcan. Pt/CNovel exhibits higher cell-voltage than Pt/Vulcan in the low current density region. This result indicates that the former has a higher ORR activity than the latter as specifically indicated in the specific activities at 0.9 V shown in Figure 1d. The trend is, however, opposite in the RDE measurements while the specific activities for both samples by RDE are higher than those measured by the MEAs. These results indicate that the Pt/CNovel suffers less catalyst poisoning by the sulfonic acid anion than Pt/Vulcan in MEAs probably because the anion linked to the ionomer cannot reach the surfaces of the Pt nanoparticles inside the mesopores of CNovel while all Pt nanoparticles on Vulcan® can be reached by the ionomer.

Electrochemical properties of gold and glassy carbon electrodes electrografted with an anthraquinone diazonium compound using the rotating disc electrode method

The RDE method was combined with the electrografting procedure to prepare thick AQ films on Au and glassy carbon electrodes.

Modified Glassy Carbon Rotating Disk Electrode for Determination of Heterogeneous Reaction Rate Constant of H2O2 Decomposition

AbstractModified glassy carbon RDE method is introduced in this work for the determination of heterogeneous reaction rate constant of H2O2 decomposition. This method is based on the analysis of RDE voltammograms of H2O2 reduction on a glassy carbon electrode covered with a catalyst layer. As a case study, the rate constant of H2O2 decomposition on nitrogen doped graphene is determined by using both glassy carbon and gold RDE methods. A good agreement is observed between the results of these two methods indicating the reliability of the glassy carbon method. Moreover, advantages and limitations of the glassy carbon method are discussed.

A rotating disk electrode study of the particle size effects of Pt for the hydrogen oxidation reaction

By using a catalyst-lean thin-film RDE method, the fast kinetics of the hydrogen oxidation reaction (HOR) on highly dispersed Pt nanoparticle electrocatalysts can be determined, free from the interference of the mass transport of H(2) molecules in solution. Measurements with carbon-supported Pt nanoparticles of different sizes thus allow revealing the particle size effect of Pt for the HOR. It is shown that there is a "negative" particle size effect of Pt on the kinetics of HOR, i.e., the exchange current density j(0) decreases with the increased dispersion (i.e. decreased mean particle size). A maximum mass activity of Pt for the HOR is found at particle sizes of 3-3.5 nm. The observed particle size effect is interpreted in terms of the size dependent distribution of surface atoms on the facets and edges, which is implied by the voltammetric responses of Pt/C catalysts with differently sized Pt particles. The accompanied decrease in the HOR activity with the increase in the edge atom fraction suggests that the edge atoms on the surface of Pt nanoparticles are less active for the HOR than those on the facets.

Preparation and Research of AuNi Cathode Catalyst for Direct Methanol Fuel Cell

AuNi alloy was synthesized by vacuum arc melting in high-purity argon atmosphere. The AuNi alloy was characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The results of EDS indicated that Au and Ni atoms were well-distributed in the alloy. Moreover, the results of XPS exhibited an electronic transfer from Ni to Au in AuNi phase. The Electrocatalytic oxygen reduction reaction (ORR) activity and the methanol tolerance of the AuNi alloy were respectively investigated using the RDE method and the electrochemical cyclic voltammetry. The results suggested that O2was directly oxidized to H2O on the AuNi catalyst via an approximate four-electron reduction pathway, and that the AuNi catalyst had a high electrocatalytic activity for the ORR and an acceptable methanol tolerance, simultaneously.

Structure-Activity Relationship of Dealloyed PtCo3 and PtCu3 Nanoparticle Electrocatalyst for Oxygen Reduction Reaction in PEMFC

We report a synthesis and study on carbon supported PtCo3 and PtCu3 alloy nanoparticle catalyst for ORR. The chemical composition of alloys was carried out with EDS. The electrochemical measurements were conducted using a thin-film RDE method. Recently, we have demonstrated that dealloyed PtCu3 nanoparticle exhibits 3-4 times higher mass activity and 4 times higher specific activity for ORR than Pt. Here, the dealloyed PtCo3 also shows about 4 fold increase in specific activity, but 2-3 fold in mass activity than Pt/C. The in-situ generated Pt rich surface of Co rich Pt alloy nanoparticle catalyst tested for ORR activity. Geometric effects based on Pt surface constitution were assumed for the high activity for ORR. PtCo3 nanoparticle catalyst seems to be an interesting opportunity for further studies for ORR. The thermodynamic instable deposition of Co and the robust Pt ECSA are probably the large advantages to other Pt alloys.

Electrochemical and Electronic Structure Investigations of the [S3N3]•Radical and Kinetic Modeling of the [S4N4]n/[S3N3]n(n= 0, −1) Interconversion

Voltammetric studies of S(4)N(4) employing both cyclic (CV) and rotating disk (RDE) methods in CH(2)Cl(2) at a glassy carbon electrode reveal a one-electron reduction at -1.00 V (versus ferrocene/ferrocenium), which produces a second redox couple at -0.33 V, confirmed to be the electrochemically generated [S(3)N(3)](-) by CV studies on its salts. Diffusion coefficients (CH(2)Cl(2)/0.4 M [(n)Bu(4)N][PF(6)]) estimated by RDE methods: S(4)N(4), 1.17 x 10(-5) cm(2) s(-1); [S(3)N(3)](-), 4.00 x 10(-6) cm(2) s(-1). Digital simulations of the CVs detected slow rates of electron transfer for both couples and allowed for a determination of rate constants for homogeneous chemical reaction steps subsequent to electron transfer. The common parameters (k(f1) = 2.0 +/- 0.5 s(-1), k(s1) = 0.034 +/- 0.004 cm s(-1) for [S(4)N(4)](-/0); k(f2) = 0.4 +/- 0.2 s(-1), k(s2) = 0.022 +/- 0.005 cm s(-1) for [S(3)N(3)](-/0) at T = 21 +/- 2 degrees C) fit well to a "square-scheme" mechanism over the entire range of data with first order decay of both redox products. An alternate model could also be fit wherein [NS](*) liberated in the first step reacts with formed [S(3)N(3)](*) to reproduce S(4)N(4) with an apparent second order rate constant k(f2)' = 1.1 +/- 0.3 x 10(3) M(-1) s(-1). The crystal structure of [PPN][S(3)N(3)] was determined by X-ray crystallography indicating the solvation of the anion by 1 equiv of methanol. The generated [S(4)N(4)](-*) radical anion was detected by the Simultaneous Electrochemical Electron Paramagnetic Resonance (SEEPR) method to give: (a) [(32)S(4)(14)N(4)](-*), 9 lines, a((14)N) = 0.118 mT; (b) [(32)S(4)(15)N(4)](-*), 5 lines, a((15)N) = 0.164 mT; (c) [(33)S(4)(14)N(4)](-*), estimated a((14)N) = 0.118, a((33)S = 0.2 mT); g = 2.0008(1). Equivalence of (33)S hyperfine splittings is consistent with dynamic averaging of the C(2v) geometry in solution. High-level electronic structure calculations provide evidence for an open-shell doublet triradicaloid character to the ground state wave function of [S(3)N(3)](*).

The preparation, crystal structure and electrochemistry of (5 Z,5′ Z)-2,2′-(alkane-α,ω-diylsulfanyldiyl)bis(5-(3-pyridylmethylene)-3,5-dihydro-4 H-imidazol-4-ones) and their complexes with cobalt(II) chloride

A series of S-alkylated derivatives of 2-thiohydantoins, containing two 5-(3-pyridylmethylene)-3,5-dihydro-4 H-imiazole-4-one fragments joined by polymethylene bridges with different numbers of carbon atoms, was synthesized. The title (5 Z,5′ Z)-2,2′-(alkane-α,ω-diylsulfanyldiyl)bis(5-(3-pyridylmethylene)-3,5-dihydro-4 H-imidazol-4-ones) ( L) were obtained by alkylation of 5-(3-pyridylmethylene)-3-phenyl-2-thiohydantoine by 1,2-dibromoethane, 1,6-dibromohexane or 1,10-dibromodecane in DMF in the presence of potassium carbonate. The complexes of ligands L with CoCl 2 · 6H 2O have been synthesized. It is shown that, regardless of the L:CoCl 2 ratio, complexes with LCoCl 2 composition are obtained in all cases. The structure of the cobalt(II) chloride complex with (5 Z,5′ Z)-2,2′-(ethane-1,2-diyldisulfanyldiyl)bis(5-(3-pyridylmethylene)-3-phenyl-3,5-dihydro-4 H-imidazol-4-one) was determined by means of the RSA method. The cobalt atom in this complex has a tetrahedral ligand environment and it is coordinated by two chloride anions and two nitrogen atoms of pyridine fragments, forming a 19-membered metallocycle. Electrochemical investigations of the synthesized ligands and complexes have been made by CVA and RDE methods. It is established that the first stage of reduction for the complexes takes place on the metal, whereas the first stage of oxidation takes place on the coordinated chloride-anions.

Cathodic oxygen reduction at the catalyst layer formed from Pt/carbon with adsorbed water

An increase in Pt utilization in polymer electrolyte fuel cell electrodes is necessary to improve performance and reduce cost. In the present study, water adsorption was carried out as a pretreatment of Pt/carbon used with Nafion ® solution to prepare a catalyst paste for electrode catalyst layer formation. Mercury porosimetry and cyclic voltammetry were used to characterize the catalyst layer, and the RDE method to investigate its activity for cathodic oxygen reduction. The results revealed that Pt utilization was increased by the pretreatment due to Nafion ® penetration into the pores of Pt/C and that oxygen reduction was enhanced at the catalyst layer.

Mechanism of electrochemical interaction between sulfur-containing amino acids and anodically polarized platinum electrode

Electrooxidation of cysteine and methionine on a platinum electrode in solutions with various pH values is studied by the RDE and linear-sweep voltammetry methods. Based on this study and previous adsorption measurements, kinetic equations and mechanisms of main processes, which occur on the anodically polarized platinum electrode in the presence of the amino acids and lead to electrocatalytic dissolution of platinum, are proposed. Anodic dissolution of platinum in the presence of cysteine and methionine is accelerated due to immediate involvement of the sulfur atom in the adsorption and electrooxidation on the platinum electrode surface.

Electrocatalytic Oxidation of Dihydric Phenol on Polypyrrole Film Modified Electrodes

The electrochemical behavior of catechol, hydroquinone and resorcinol on GC and PPy/GC electrode surface were studied by CV and RDE method. The results indicated that these three substance could be oxidized electrocatalytically on PPy film electrode. The possibility of fabrication of amperometric electrochemical sensor for catechol was also studied.

Absolute determination of electron consumption in transient or steady state electrochemical techniques

A method elaborated from original work by Lingane is discussed and used to determine the absolute value of the electron stoichiometry corresponding to any electrochemical wave, under the exact conditions of its observation. The method is based on comparison of the currents measured by a pair of microscale techniques such as chronoamperometry, cyclic voltammetry, RDE or steady state methods at microelectrodes. From an evaluation of the uncertainties associated with the use of each possible pair, it is concluded that the best choice consists in chronoamperometry and a steady state method at a microelectrode. The experimental validity of the method is examined in five different cases pertaining to organic or organometallic electrochemistry, in which the determination of the absolute value of the number of electrons exchanged leads to important mechanistic or synthetic consequences.

Spectrometric oil analysis: Atomic emission spectrometric analysis of wear metals in lube oils by RDE method

Analyse des huiles par spectrometrie. Analyse des metaux uses dans les huiles lubrifiantes par spectrometrie d'emission atomique avec la methode de l'electrode disque rotative (rotating disk electrode)

Investigations on electrodeposition of nickel from dimethylsulfoxide

Process of cathodic deposition of nickel mainly from Ni(BF 4) 2 solution in DMSO has been investigated using various experimental techniques. It has been found that this process is complicated. The collected experimental data indicate that passivation of fresh cathodic layer of Ni by chemisorption of DMSO molecules takes place. By basing on the rde methods the values of α n m = 0.4 (± 0.05) and k fh = f( E c ) have been estimated.

Investigations on electroreduction of TiCl 4 in dimethylsulfoxide

The process of electroreduction of TiCl 4 in DMSO has been investigated by cyclic voltammetry and rde methods. It has been found that the first step of the cathodic reaction is reduction of Ti(IV) to Ti(III) with α = 0.38 and k f = 6.5210 −4 cms −1. It has also been found that a secondary chemical reaction follows the TiCl 4 reduction in DMSO. Products of these reactions may behave as inhibitors of cathodic processes and in consequence the rate of the latter decreases. The mechanism of electroreduction of TiCl 4 to Ti(III), Ti(II) and Ti(0) has been suggested. The purpose of the investigation was to determine the effect of solvent type on the kinetics and the mechanism of the electroreduction process of TiCl 4. The results obtained with the use of acetonitrile (AN) and dimethylformamide (DMF) solutions have been discussed previously ( Electrochim. Acta 25, 1209 (1980) and Elektrokhimya (1981), in press).