Cristina Flox

Highly electrocatalytic flexible nanofiber for improved vanadium-based redox flow battery cathode electrodes

A flexible nanofiber-based electrode material is proposed as cathode in a vanadium-based flow battery (VRFB), allowing the design of innovative VRFB configuration geometries. Its estimated electrochemical surface area is 350 cm2 cm−3, doubling that of commercial PAN-felt.

Electron Bottleneck in the Charge/Discharge Mechanism of Lithium Titanates for Batteries

The semi-solid flow battery (SSFB) is a promising storage energy technology featured by employing semi-solid fluid electrodes containing conductive additive and active Li-ion battery materials. The state of art anode material for SSFB is Li4Ti5O12 (LTO). This work shows that LTO improves drastically the performance in fluid electrode via hydrogen annealing manifesting the importance of the electrical conductivity of the active material in SSFBs. On the other hand, the properties of fluid electrodes allow the contributions of ionic and electrical resistance to be separated in operando. The asymmetric overpotential observed in Li4Ti5O12 and TiO2 is proposed to originate from the so-called electron bottleneck mechanism based on the transformation from electrically insulator to conductor upon (de-)lithiation, or vice versa, which should be considered when modelling, evaluating or designing advanced materials based on Li4Ti5O12, TiO2 or others with insulating-conducting behavior materials.

Hydrogen-Treated Rutile TiO2 Shell in Graphite-Core Structure as a Negative Electrode for High-Performance Vanadium Redox Flow Batteries

Hydrogen-treated TiO2 as an electrocatalyst has shown to boost the capacity of high-performance all-vanadium redox flow batteries (VRFBs) as a simple and eco-friendly strategy. The graphite felt-based GF@TiO2 :H electrode is able to inhibit the hydrogen evolution reaction (HER), which is a critical barrier for operating at high rate for long-term cycling in VRFBs. Significant improvements in charge/discharge and electron-transfer processes for the V3+ /V2+ reaction on the surface of reduced TiO2 were achieved as a consequence of the formation of oxygen functional groups and oxygen vacancies in the lattice structure. Key performance indicators of VRFB have been improved, such as high capability rates and electrolyte-utilization ratios (82 % at 200 mA cm-2 ). Additionally, high coulombic efficiencies (ca. 100 % up to the 96th cycle, afterwards >97 %) were obtained, demonstrating the feasibility of achieving long-term stability.

Solid electrolyte interphase in semi-solid flow batteries: a wolf in sheep's clothing

The formation of the alkyl carbonate-derived solid electrolyte interphase (SEI) enables the use of active materials operating at very cathodic potentials in Li-ion batteries. However, the SEI in semi-solid flow batteries results in a hindered electron transfer between a fluid electrode and the current collector restricting the operating potentials to ca. 0.8 V vs. Li/Li(+) for EC-based electrolytes.

Pd2Sn [010] nanorods as a highly active and stable ethanol oxidation catalyst

The development of highly active, low cost and stable electrocatalysts for direct alcohol fuel cells remains a critical challenge. While Pd2Sn has been reported as an excellent catalyst for the ethanol oxidation reaction (EOR), here we present DFT analysis results showing the (100) and (001) facets of orthorhombic Pd2Sn to be more favourable for the EOR than (010). Accordingly, using tri-n-octylphosphine, oleylamine (OLA) and methylamine hydrochloride as size and shape directing agents, we produced colloidal Pd2Sn nanorods (NRs) grown in the [010] direction. Such Pd2Sn NRs, supported on graphitic carbon, showed excellent performance and stability as an anode electrocatalyst for the EOR in alkaline media, exhibiting 3 times and 10 times higher EOR current densities than that of Pd2Sn and Pd nanospheres, respectively. We associate this improved performance with the favourable faceting of the NRs.

Static and Dynamic Studies on LiNi1/3Co1/3Mn1/3O2‐Based Suspensions for Semi‐Solid Flow Batteries

Abstract LiNi1/3Co1/3Mn1/3O2 (LNCM)‐based suspensions for semi‐solid flow batteries (SSFB) have been investigated by galvanostatic charge/discharge an electrochemical impedance spectroscopy (EIS). The resistance and electrochemical performance of half cells (vs. Li/Li+) as well as the rheological properties are affected by the content of a commercially available electroconductive carbon black [KetjenBlack (KB), AkzoNobel] in the suspensions. In static conditions, a cell with 11.87 and 13.97 % by volume of KB and LNCM delivers high capacity 130 mA h g−1 at 5 mA cm−2, respectively, and a coulombic efficiency of 90 % over 10 injections. The impedance of half cells is dominated by a contact resistance fitted with a resistor and a constant phase element (CPE) in parallel. In flow conditions, cell potential depends on applied current density and measured over potentials are ∼0.3 and 0.7 V for 0.33 and 1 mA cm−2, respectively, for a cell containing a suspension with 9.53 % in volume of KB and 13.90 % in volume of LNCM. The effect of the cell contact resistance on the electrochemical performance is discussed.

Advanced nanomaterials for energy-related applications

1Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA 2School of Materials Science and Engineering, Yeungnam University, Gyeongsan 712-749, Republic of Korea 3Catalonia Institute for Energy Research, Jardins de les Dones de Negre, e1, Sant Adrià de Besòs, 08930 Barcelona, Spain 4State Key Laboratory of Material Processing and Die & Mould Technology, Huazhong University of Science and Technology, Wuhan 430074, China 5School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China 6Engineering Laboratory for Functionalized Carbon Materials, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China

Role of bismuth in the electro-kinetics of silicon photocathodes for solar rechargeable vanadium redox flow batteries

The ability of crystalline silicon to photoassist the V3+ /V2+ cathodic reaction under simulated solar irradiation, combined with the effect of bismuth have led to important electrochemical improvements. Besides the photovoltage supplied by the photovoltaics, additional decrease in the onset potentials, high reversibility of the V3+ /V2+ redox pair, and improvement in the electrokinetics were attained thanks to the addition of bismuth. In fact, Bi0 deposition has shown to slightly decrease the photocurrent, but the significant enhancement in the charge transfer, reflected in the overall electrochemical performance clearly justifies its use as additive in a photoassisted system for maximizing the efficiency of solar charge to battery.

A Perspective: Could Carbon Current Collectors Improve the Energy Density of Aqueous Alkaline Symmetric Supercapacitors?

Abstract The present discussion shows a perspective about using graphite as a current collector in order to achieve high energy density in a symmetric supercapacitor system. Several electrochemical modes (such as rest potential analysis, CV, PEIS, GCPL) were carried out to evaluate the electrochemical characteristics of graphite in aqueous 6 mol/L KOH. And, the resulting performance was compared to an another conventional current collector system based on nickel-stainless steel. Interestingly, widening of cell voltage was observed for graphite when compared to nickel-stainless steel. The discussion reveals the reasonable influences and validations of widening in cell voltage towards the values in energy densities. This perspective also highlights some issues related to carbon (graphite) current collectors and encloses with some promising strategies in overcoming these issues, not limiting the domain of application (either micro or macro supercapacitor devices).

Non-aqueous semi-solid flow battery based on Na-ion chemistry. P2-type NaₓNi₀̣₂₂Co₀̣₁₁Mn₀̣₆₆O₂-NaTi₂(PO₄)₃

We report the first proof of concept for a non-aqueous semi-solid flow battery (SSFB) based on Na-ion chemistry using P2-type NaxNi0.22Co0.11Mn0.66O2 and NaTi2(PO4)3 as positive and negative electrodes, respectively. This concept opens the door for developing a new low-cost type of non-aqueous semi-solid flow batteries based on the rich chemistry of Na-ion intercalating compounds.