Robert Lynch

University of Limerick | UL · Department of Physics & Energy

In this study, we investigate the effect of electrochemical treatment on the VII-VIII kinetics at glassy carbon electrodes in electrolytes at a range of pH. The resulting electrode kinetics of the vanadium redox couples at each treatment potential are studied using electrochemical characterization techniques including cyclic voltammetry (CV) and el...

Demand for energy stability and balancing of electricity is growing rapidly, driven by the increased use of energy from renewable sources such as the sun, wind and ocean. Due to the intermittency and/or unpredictability of such sources, there is a growing need for energy storage solutions that allow such energy to be harvested when available and st...

Two aspects of vanadium flow batteries are reviewed: electrochemical kinetics on carbon electrodes and positive electrolyte stability. There is poor agreement between reported values of kinetic parameters; however, most authors report that kinetic rates are faster for V IV /V V than for V II /V III . Cycling the electrode potential increases the ra...

Electrodes for vanadium flow batteries (VFBs) are typically fabricated from carbon felt or carbon paper, although other novel materials are also being investigated. For optimum performance, electrodes are usually thermally pretreated in air, although a variety of chemical and electrochemical treatments are also being investigated. The electrode kin...

Electrodes are key components of any battery system: they are the sites where the electrical potentials are generated that ultimately power the battery. In this chapter we discuss electrodes for VRFBs. We describe the requirements and the available technology, materials and processes. We then discuss the kinetics of the reactions at the electrodes...

Vanadium flow batteries are an effective technology for storage of energy from renewable sources such as wind or solar. The vanadium redox reactions occur at carbon-based electrodes in both half-cells. The kinetics of the vanadium reactions is strongly affected by treatment (e.g., thermal, chemical, or electrochemical) of the carbon electrodes. Oxy...

Flow batteries are a promising technology for flexible large-scale energy storage systems to tackle the problem of intermittency with renewable energy sources. Several flow battery systems have been successfully developed and deployed to date, including all-vanadium, zinc-iron, zinc-bromine, and all-iron flow batteries. ¹ Among these, vanadium flow...

All-Vanadium Flow Batteries (VFBs) are an attractive technology for energy storage, especially in conjunction with a renewable energy source such as wind or solar ¹ . The cells typically have carbon felt electrodes for both half-cells and are separated by an ion-exchange membrane. The catholyte and the anolyte circulate through the electrodes from...

Vanadium Flow Batteries (VFBs) are a promising energy storage technology, particularly for large and medium scale applications. In a VFB, energy is stored in two vanadium electrolytes separated by a nafion membrane. The use of vanadium electrolytes in both half-cells minimises cross contamination issues which have plagued other flow battery chemist...

The redox flow battery (RFB) has seen an explosion in research activity in recent years due to its attractiveness for large-scale energy storage applications ( e.g. grid level storage). RFBs 1,2 offer many advantages over conventional batteries including their relatively high reliability and long cycle life, as well as the ability to scale their en...

In this paper we demonstrate our ability to make accurate in- situ measurements of both the state-of-charge and the concentration of individual vanadium species in a lab scale vanadium flow battery. The analysis is based on our previously published characterization of the spectroscopy of mixed solutions of V II /V III and V IV /V V . Measurements o...

The effect of the electrochemical treatments on the electrode kinetics of the positive and negative half-cell reactions in vanadium flow batteries was investigated by controlling treatment potentials. In general, V IV -V V electrode kinetics are enhanced at cathodic treatment potentials but are inhibited at anodic treatment potentials. In contrast,...

Cyclic voltammetry and electrochemical impedance spectroscopy were used to investigate the effect of electrochemical treatment of glassy carbon electrodes in electrolytes of various pH on V IV /V V redox kinetics. In all pH treatment electrolytes (pH 0 – pH 6.3), the V IV /V V kinetics are enhanced by cathodic treatment of the electrode and inhibit...

The electrochemical kinetics of the V II /V III redox reaction on carbon electrodes is enhanced by anodic treatment of the electrode and inhibited by cathodic treatment. Contrastingly, the kinetics of the V IV /V V redox reaction is inhibited by anodic treatment of the electrode and enhanced by cathodic treatment. The observed effects are attribute...

Effect of electrochemical treatment on the VIV/VV kinetics at glassy carbon electrodes following treatment in various electrolyte pHs was investigated. For all pHs (pH 0 – pH 6.3), the VIV/VV kinetics are enhanced by cathodic treatment of the electrode and inhibited by anodic treatment. Activating effect of cathodisation increased markedly with inc...

An investigation was carried out into the supporting electrolytes that could be used for vanadium flow batteries (VFBs). Acidic supporting-electrolytes are typically used in VFBs 1 and there are very few papers published on alkaline supporting-electrolytes for VFBs or on the influence of electrolyte pH on the performance of VFBs. Thus, we preformed...

Using our standard methodology, we examined the thermal stability of vanadium flow battery positive electrolytes over a range of temperature from 30 to 70 °C with stable lifetimes from 11 min to 87 days. At higher temperatures (45 °C–70 °C) measurements showed excellent reproducibility but at lower temperatures (30 °C–45 °C) showed some scatter. Me...

There is presently great interest in redox flow batteries ¹⁻⁸ (RFBs) for large-scale energy storage ⁹ due to advantages over other electrical energy storage (EES) technologies, and research activities in this area have grown exponentially in recent years. The vanadium flow battery (VFB), also known as the vanadium redox flow battery (VRFB), is comm...

Electrochemical etching of semiconductors under anodic conditions can lead to the growth of nanoporous structures. There has been extensive research in this area for silicon and III-V electrodes ¹⁻⁷ . Porous structures are obtained ³⁻⁷ when n-InP is anodized in aqueous KOH at concentrations of 2 mol dm ⁻³ or greater; planar etching occurs below 1 m...

The electrochemical kinetics of the V II -V III reaction on carbon electrodes is enhanced by anodic treatment and inhibited by cathodic treatment. In contrast, the kinetics of V IV -V V is inhibited by anodic treatment and enhanced by cathodic treatment. Rate constants are greater for V IV -V V than for V II -V III under comparable conditions. The...

In the early stages of anodization of n-InP in KOH, isolated nanoporous domains form and eventually merge into a continuous layer. SEM and TEM cross-sections show clear evidence that these have the shape of truncated tetrahedrons and result from preferential pore progagation along the <111>A directions. We propose a three-step model of electrochemi...

Using our standard methodology, we have examined the stability of electrolytes with compositions close to those used in actual flow batteries over a range of temperature from 70 to 30°C. Measurements at higher temperatures (45–70°C) showed excellent reproducibility but measurements at lower temperatures (30–45°C) showed some scatter. Furthermore, t...

There is great interest in redox flow batteriesfor large-scale energy storage ¹⁻⁸ . The energy storage capability and power output of a flow battery, unlike conventional batteries, can be scaled independently to suit the desired application. 4,8 Other advantages ⁹ include a high degree of safety, long lifetime, potentially low capital costs, high r...

Etching of III-V semiconductors is often observed to be anisotropic. For example both chemical and electrochemical etching of III-V semiconductors show preferential etching of {111}B planes ( i.e. group-V-terminated planes). 1,2 The slowest-etching plane is usually {111}A and so these facets are revealed during etching of InP, GaAs and GaP. Due to...

Vanadium flow batteries (VFBs) are an attractive technology for a variety of energy storage applications ¹⁻⁴ . An important advantage of a flow battery is that its energy storage capacity and its power capability can be scaled independently. VFBs have the additional advantage that cross-contamination due to transport through the membrane is effecti...

The redox flow battery (RFB) has seen an explosion in research activity in recent years due to its attractiveness for large scale energy storage applications ( e.g. grid level storage). ¹⁻⁵ RFBs offer many advantages over conventional batteries including their relatively high reliability and long cycle life, as well as the ability to scale their en...

There is a significant need for a technique to determine the concentration of V V in vanadium flow battery (VFB) catholytes (concentrated mixtures of V IV (vanadyl; typically in the form of VO ⁺⁺ ions) and V V (pervanadyl; typically in the form of VO 2 ⁺ ions) in H 2 SO 4 ). A large number of studies on VFB catholytes are concerned with either the...

Developing sustainable and efficient thermoelectric materials is a challenge because the most common thermoelectric materials are based on rare elements such as bismuth and telluride. In this context, we have produced bio-based carbon nanofibres (CNFs) derived from mixtures of polyacrylonitrile and lignin using electrospinning. The addition of lign...

Recent decades have seen huge growth in the renewable energy sector, spurred on by concerns about climate change and dwindling supplies of fossil fuels. One of the major difficulties raised by an increasing reliance on renewable resources is the inflexibility when it comes to controlling supply in response to demand. For example, solar energy can o...

Anodization of n-InP electrodes was carried out over a range of temperatures and KOH concentrations. Scanning electron microscopy showed <111A>aligned pore growth with pore width decreasing as the temperature was increased. This variation is explained in terms of the relative rates of electrochemical reaction and hole diffusion and supports the thr...

Nanotechnology is an area of growing industrial importance and there is considerable interest in the fabrication and characterisation of nano-scale structures for various applications. Although considerable progress has been made in developing technology for such applications, the underlying fundamentals are not always well understood and many impo...

The stability of VFB catholytes was investigated using both light-scattering measurements and visual observation. V 2 O 5 precipitates after an induction time τ which shows an Arrhenius variation with temperature. The value of τ increases with increasing [S] and with decreasing [V V ] but the activation energy remains constant with a value of (1.79...

Electrodeposited metal films are often in a state of stress and this has been the subject of extensive experimental investigation and theoretical analysis ¹⁻⁴ . We have been measuring stress development in situ during electrodeposition and correlating the results with in-situ AFM imaging during electrodeposition under similar conditions. In this pa...

The increasing use of non-dispatchable sources of renewable energy such as wind, wave and solar is driving a growing demand for large- and medium-scale energy storage technologies. ¹ All-vanadium flow batteries (VFBs), are a promising technology for such applications. ²⁻⁸ VFBs have a major advantage over other flow batteries in that issues arising...

In semiconductor materials, electrochemical processes during anodization can cause localized etching to occur. 1,2 This localized etching leads to dissolution of material in a way that creates complex porous structures. Such structures are of considerable interest. With silicon, crystals can be engineered that behave as though they have a direct ba...

This focus issue addresses some of the cutting edge research themes in many processes that occur at the interface between a semiconductor and a solution. This interface, a pH and redox potential-controlled liquid analog to the metal-semiconductor interface, is where semiconductor electrochemistry occurs. With the advent of alternative approaches to...

The anodic formation of porosity in semiconductors has received considerable attention, due to the fundamental insight it offers into semiconductor etching properties and its wide range of possible applications [1]. Although a number of models have been proposed to explain the formation of porosity in semiconductors [2-5], none as yet has been show...

Thin metal films deposited on a substrate are usually in a state of stress and this has been the subject of extensive experimental investigation and theoretical analysis. [1-4] Various studies of the stress generated during the electrodeposition and aging of copper films have been reported. In this paper we report results of in situ stress monitori...

Accurate knowledge of the physical properties of electrolytes is of great importance when designing, running or modelling flow battery systems. Typically, the vanadium concentration in vanadium flow battery (VFB) electrolytes is limited to about 1.6 mol dm ⁻³ . This is primarily due to the gradual precipitation of V V from VFB catholytes at high va...

The stability of typical vanadium flow battery (VFB) catholytes was investigated at temperatures in the range 30-60°C for VV concentrations of 1.4-2.2 mol dm⁻³ and sulfate concentrations of 3.6-5.4 mol dm⁻³. In all cases, V2O5 precipitates after an induction time, which decreases with increasing temperature. Plots of the logarithm of induction time...

This paper describes variations in current density observed in linear sweep voltammetry curves during the anodization of n-InP in aqueous KOH electrolyte and how these variations arise. The analysis is performed by stopping the anodization after different durations of etching and observing via scanning electron microscopy and other techniques the p...

Vanadium flow batteries (VFBs) are a promising technology because, in addition to having long cycle life, they are essentially immune to cross contamination problems due to mass transfer across the membrane [1]. The energy efficiency of batteries depends on the voltage and coulombic efficiency. Voltage inefficiency can arise due to sluggish electro...

Vanadium flow batteries (VFBs), also known as vanadium redox flow batteries (VRFBs), are an attractive technology for a variety of energy storage applications ¹⁻⁴ . An important advantage of a flow battery is that its energy storage capacity and its power capability can be scaled independently. VFBs have the additional advantage that cross-contamin...

The anodic formation of porosity in semiconductors has received considerable attention, due to the fundamental insight it offers into semiconductor etching properties and its wide range of possible applications [1]. Although a number of models have been proposed to explain the formation of porosity in semiconductors [2-5], none as yet can explain t...

Using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), it was shown for four different types of carbon that electrode treatments at negative potentials enhance the kinetics of V IV -V V and inhibit the kinetics of V II -V III while electrode treatments at positive potentials inhibit the kinetics of V IV -V V and enhance the...

The stability of vanadium flow battery (VFB) catholytes was investigated using both lightscattering measurements and visual observation. V 2 O 5 precipitates after an induction time τ which shows an Arrhenius variation with temperature. The value of τ increases with increasing concentration of sulfate and with decreasing concentration of V V but th...

Both visual observation and light-scattering measurements were used to investigate the stability of typical vanadium flow battery (VFB) catholytes. V2O5 precipitates after an induction time that decreases with increasing temperature and concentration of VV and increases with concentration of sulphate. This was observed at 30-60°C for VV and sulphat...

Pores formed anodically in InP at different temperatures, electrolyte (KOH) concentrations, carrier concentrations and current densities exhibit significant pore width variations. The pore width decreases as the temperature, carrier concentration or current density are increased. The pore width also decreases when the KOH concentration is increased...

Using a substrate curvature method, stress was monitored in-situ in acidic CuSO4 electrolytes with and without chloride as an additive. Chloride in the electrolyte considerably reduced the tensile stress. Chloride-free and chloride-containing electrolytes also showed very different behaviors after interruption of electrodeposition. In chloride-free...

The stability of typical vanadium flow battery (VFB) catholytes with respect to precipitation of V2O5 was investigated at temperatures in the range 30–60°C. In all cases a precipitate formed after an induction time, which decreased with increasing temperature and concentration of VV and increased with concentration of sulfate. Arrhenius-type plots...

Research on semiconductor nanostructures is motivated by two key considerations. The first is the continuing call for smaller and more efficient versions of existing semiconductor devices. The second is the characterisation and exploitation of the unique characteristics that are often exhibited by structures at the nano-scale. While a wide variety...

There is considerable interest in vanadium flow batteries (VFBs) for storage of electrical energy, particularly in conjunction with renewable energy sources such as wind and solar ¹ . Like other flow battery systems the VFB is an electrochemical device that converts electrical energy to chemical energy which is stored in the electrolyte ² . Typical...

Thin metal films deposited on a substrate are usually in a state of stress and this has been the subject of extensive experimental investigation and theoretical analysis ¹⁻⁴ . Various studies of the stress generated during the electrodeposition and aging of copper films have been reported. In this paper we report results of in situ stress monitorin...

There is considerable interest in flow batteries for storing energy from non-dispatchable power sources such as solar and wind energy. ¹⁻³ Vanadium flow batteries (VFB), ³⁻¹² also known as vanadium redox flow batteries (VRFB or VRB), are particularly attractive because, in addition to having long cycle life, they are essentially immune to cross-con...

The energy efficiency of batteries is dependent on their voltage efficiency and coulombic efficiency. Voltage inefficiencies arise due to sluggish electrode kinetics and, as a result, large overpotentials at the electrode. Furthermore, the higher the overpotential the greater the number of side reactions such as hydrogen formation ¹⁻⁷ at the negati...

There is considerable interest in flow batteries for storing energy from non-dispatchable power sources such as solar, wind and ocean energy and for other large and medium scale energy storage applications. Vanadium flow batteries (VFB), also known as vanadium redox flow batteries (VRFB or VRB), are particularly attractive because, in addition to h...

Novel carbon fiber microelectrode (CFME) and flow cell experiments were used to investigate electrode treatments for vanadium flow batteries (VFBs). Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) on CFMEs showed that electrode treatments at positive potentials enhance the kinetics of V²⁺ /V³⁺ and inhibit the kinetic...

Electrochemical impedance spectroscopy and cyclic voltammetry were used to investigate the electrode kinetics of V II-V III and V IV-V V in H 2 SO 4 on glassy carbon, carbon paper, carbon xerogel, and carbon fibers. It was shown that, for all carbon materials investigated, the kinetics of V II-V III is enhanced by anodic, and inhibited by cathodic,...

Electrochemical impedance spectroscopy and cyclic voltammetry were used to investigate the electrode kinetics of VII-VIII and VIV-VV in H2SO4 on glassy carbon, carbon paper, carbon xerogel, and carbon fibers. It was shown that, for all carbon materials investigated, the kinetics of VII-VIII is enhanced by anodic, and inhibited by cathodic, treatmen...

The formation of sub-surface truncated tetrahedral voids beneath suspended ~40 nm thick dense InP shelves is achievable via a two-step etching method. The first step involves the electrochemical anodisation of n-type InP in aqueous KOH electrolyte resulting in the formation of truncated tetrahedral domains of pores beneath an ~40 nm thick dense sur...

Anodization of highly doped (10¹⁸ cm⁻³) n-InP in 2 – 5 mol dm⁻³ KOH under potentiostatic or potentiodynamic conditions results in the formation of a nanoporous sub-surface region. Pores originate from surface pits and an individual, isolated porous domain is formed beneath each pit in the early stages of anodization. Each such domain is separated f...

This is a working paper discussing the use of spectroscopic measurement to determine the state of charge of vanadium flow batteries.

The ultraviolet-visible spectra of catholytes for vanadium flow batteries (VFBs) were measured and analyzed for a range of VIV:VV ratios and vanadium concentrations. Using a model of V2O33+ in equilibrium with VO2+ and VO2+, the spectra were characterized in terms of an excess absorbance parameter p and the molar extinction coefficients ε4 and ε5 o...

Electrochemical reactions in all-vanadium flow batteries (VFBs) were investigated by examining the effects of electrochemical treatments of carbon on the electrode kinetics of the oxidationreduction reactions of both VIV/VV and VII/VIII. A range of carbon materials were investigated including carbon fibers, glassy carbon, reticulated vitreous carbo...

As has been previously described, ¹⁻⁵ anodic etching of n-type InP, under certain conditions, leads to the formation of domains of pores beneath an ~40-nm-thick, near-surface layer of dense InP. These domains have a characteristic truncated tetrahedral domain shape – as illustrated in the schematic of Fig. 1a – displaying triangular (01-1) and trap...