Adsorption of anions on smooth platinum electrodes

184

183

The electrochemical behavior of a promising hydrogen/bromine redox flow battery is investigated for grid-scale energy-storage application with some of the best redox-flow-battery performance results to date, including a peak power of 1.4 W/cm 2 and a 91% voltaic efficiency at 0.4 W/cm 2 constant-power operation. The kinetics of bromine on various materials is discussed, with both rotating-disk-electrode and cell studies demonstrating that a carbon porous electrode for the bromine reaction can conduct platinumcomparable performance as long as sufficient surface area is realized. The effect of flow-cell designs and operating temperature is examined, and ohmic and mass-transfer losses are decreased by utilizing a flow-through electrode design and increasing cell temperature. Charge/discharge and discharge-rate tests also reveal that this system has highly reversible behavior and good rate capability. The environmental concerns and limited resources of fossil fuels have stimulated research for renewable energy sources such as wind and solar energy. Globally, there is 94 GW of electricity-generating wind power as of 2007, and it is estimated to reach 474 GW by 2020. 1The electricity from solar photovoltaics is growing at 40% per year worldwide, and the United States has targeted 100 GW of solar power by 2020.1 However, the electricity from these and other renewable resources is not constant and reliable due to their sensitive response to local weather conditions. To level out the variable generation of energy, large-scale electrical-energy storage (EES) is required. For the energy storage and load leveling, redox-flow batteries (RFB) have been considered as promising candidates due to their independently controllable power and energy, rapid response time, and high energy efficiency. Extensive research has been performed on RFB systems, including iron-chromium, all-vanadium, sodium-polysulfide, etc. 2-5However, due to the challenging issues such as low cell performance, power density, durability, and high electrolyte cost, their wide-spread adoption has not been realized. For example, the all-vanadium system, which is considered one of the closest to commercialization, utilizes a relatively expensive reactant and achieves power densities that are on the order of 0.2 to 0.7 W/cm 2 with relatively low efficiency. A hydrogen/bromine system is proposed as the reactants are earth-abundant and inexpensive and, as will be shown, high performance with high efficiency is obtainable.Yeo and Chin first investigated the hydrogen/bromine flow battery and reported excellent electric-to-electric efficiency, introducing it as a promising RFB system for energy-storage applications.6 The operating principle of the H 2 /Br 2 RFB can be described with a typical cell structure as in Figure 1. During discharge, a solution of Br 2 in HBr (aq) is fed into the cathode compartment where bromine reacts with protons supplied from the anode side and is reduced to bromide, generating the theoretical electric potential of 1.098 V at 25• C. The redu...

Section: Hmentioning

confidence: 99%

High Performance Hydrogen/Bromine Redox Flow Battery for Grid-Scale Energy Storage

Cho

Ridgway

Weber

et al. 2012

184

183

“…Finally, Table I entries and other studies reveal that considerable confusion exists over the role of adsorbed bromine in the electrode reaction. Equilibrium values for the degree of coverage of platinum surfaces with adsorbed bromine indicate that as many as 55-60% of the available adsorption sites are covered (9,10). Also, bromine is known to be strongly chemisorbed on platinum (11)(12)(13).…”

Section: V-t or V-h Vmentioning

confidence: 99%

A Model of the Bromine/Bromide Electrode Reaction at a Rotating Disk Electrode

White

Lorimer

1983

A mathematical model is presented for the Br2/Br− electrode reaction at a rotating disk electrode. The model includes current density‐overpotential expressions for the electrode reaction according to either the Volmer‐Heyrovsky (V‐H) or the Volmer‐Tafel (V‐T) mechanism and the transport equations including the effect of ionic migration. The model is used to predict current‐overpotential curves for various cases of interest. Qualitative comparison of the model predictions to literature data shows that either the V‐H or the V‐T mechanism, with V controlling, may be acceptable for the Br2/Br− reaction.

“…7 Bagotzky et al reported that the chemisorbed I − , Br − , Cl − ions, and organic species present on smooth platinum electrode surface affect the distribution of adsorbed hydrogen and therefore the H upd area. 36 The adsorption of halides on platinum is a complex process and it is affected by several factors including the crystal facets, concentration of the halide species, pH, potential and the temperature. [37][38][39][40][41] Most z E-mail: nmanoj@iitb.ac.in of these investigations were conducted under ultra-high vacuum conditions using single crystal surfaces.…”

mentioning

confidence: 99%

Recovery of Active Surface Sites of Shape-Controlled Platinum Nanoparticles Contaminated with Halide Ions and Its Effect on Surface-Structure

Devivaraprasad¹,

Kar²,

Leuaa³

et al. 2017

The interaction of halide ions (I − , Br − , Cl − ) with well-cleaned faceted platinum (nanocube, cuboctahedral) nanoparticles and platinum polycrystalline is investigated in 0.5 M H 2 SO 4 electrolyte. Under electrochemical conditions, the Pt surface gets poisoned with halide ad-atoms and it causes the attenuation of both hydrogen adsorption/desorption in the lower potential region (0.06-0.4 V) and electroxidation of Pt nanoparticles in the higher potential region (0.6-1.2 V). Above certain concentration (5 × 10 −6 M), the strongly adsorbing I − ions mask the H upd features. On the other hand, Br − and Cl − ions alter the peak features in the H upd region, those are characteristic of different Pt surface sites. On excursion to higher potentials (∼>1.2 V), concurrent halogen evolution, Pt oxidation, and oxygen evolution are observed; the increase in peak intensity in the H upd region reflects the reconstruction of the Pt surface. To remove the adsorbed halide ions from the Pt surface, an in-situ potentiostatic method is employed, which involves holding the working electrode at ∼0.03 V in 0.1 M NaOH solution. The cleanliness and retention of surface-structure are confirmed from the voltammograms recorded in the test electrolyte and the recovery of oxygen reduction reaction (ORR) activity after cleaning the Br − ion-contaminated Pt surface supports this conjecture. Anions specifically adsorbed on precious metal surfaces adversely impact several electrochemical reactions including oxidation/ reduction, metal deposition, corrosion and dissolution.1-6 Catalyst poisoning by the adsorbed anions (halides, sulfates and others) is a well-known phenomenon and it decreases the activity of electrocatalysts; for example, in fuel-cell, batteries and electrolyzers. 7,8 Especially platinum, a material for catalyzing a variety of electrochemical reactions, is prone to get poisoned in the presence of adatoms/adsorbates/solution anions under electrochemical conditions. Thus, oxygen reduction reaction (ORR) in fuel cells is affected by the adsorbed species or impurities and it is highly dependent on the cleanliness and surface structure of the catalyst. [9][10][11][12][13] In hydrogen-bromine fuel cells, bromides and bromine species migrate across the membrane and poison the hydrogen-electrode catalyst; moreover, Pt dissolves in Br − ion-containing solutions. 22-35 Most of the available surface sensitive techniques were used to elucidate adsorbate coverage and structure. Such techniques, including auger electron spectroscopy (AES), low energy electron diffraction (LEED), second harmonic generation (SHG), surface X-ray scattering (SXS), electrochemical scanning tunneling microscope (ESTM) 31,34 and electrochemical quartz crystal microbalance (EQCM), used to investigate anion adsorption have offered significant insight on the dependence of adsorption process on exposed single crystal orientations. Thus, AES/LEED studies revealed that Cl − ion adsorption occurs on Pt(100) surface at lower potential than that with Pt(111) surfaces, indi...