We will fulfil the promise of a decarbonised future

Abstract

Elestor’s hydrogen–iron flow battery architecture is put to the test and evaluated under continuous, commercially relevant operating conditions to assess durability, performance stability, and lifetime potential. The system combines a hydrogen gas circuit with an aqueous iron-based electrolyte, enabling independent scaling of power and energy while relying on abundant, low-cost active materials (±2.8€/kWh, enable reaching 15€/kWh CAPEX and 0.02€/kWh Levelized Cost of Storage at system level).

An extended continuous cycling campaign demonstrates stable operation at practical current density, temperature, and voltage windows representative of real-world deployment. Measured performance remains stable and fully recoverable through standard conditioning procedures. The absence of structural or electrochemical failure under sustained operation provides a robust empirical basis for extrapolating operational lifetimes of 20–25 years under standard use profiles.

This work positions hydrogen–iron flow battery technology as a durable, scalable, and economically viable solution for long-duration energy storage.

Abstract

Due to recent declines in the cost of photovoltaic solar generators (PV) and battery energy storage systems (BESS), baseload renewable energy systems (BRES) can now outcompete a grey generation mode (diesel electricity generation) on a 24/7 basis. BRES now promise a 30% reduction in electricity generation costs compared to diesel generators for a wide set of geographies, often reducing generation costs by 100 EUR/MWh. This gap is expected to grow with the introduction of cheaper long duration energy storage (LDES) systems in the future, potentially reducing cost of electricity supply by 50% compared to diesel generation.

With economic arguments in favour of BRES, a movement towards deployment of such systems can be expected and is also encouraged and supported by the writers of this white paper.

Numerous islands will have to overcome various hurdles though trying to implement BRES. Examples of such hurdles are shortage of development & financing capabilities as well as the shortage of land and a lock-in of diesel generation assets.

Abstract

Sulfonated poly (ether ketone) (SPEEK), perfluorosulfonic acid (PFSA), and polyvinylidene fluoride (PVDF) were wire-electrospun. Subsequently, multiple electrospun layers in different arrangements were hot-pressed into sustainable membranes for use in hydrogen-bromine flow batteries (HBFBs). The relationship between the electrospun layer composition and arrangement, membrane properties, and battery performance was explored. Wire-electrospinning and hot-pressing improved SPEEK and PFSA/PVDF compatibility, yielding dense membranes. Higher SPEEK contents lead to rougher morphologies, while the insulating nature of PVDF decreases the ion exchange capacity (IEC) and HBr uptake compared to commercial PFSA. The multi-layer assembly negatively impacted the membrane transport properties compared to the single-layer arrangement. Although wire-electrospinning improves the polymer dispersion and fixed charge density, SPEEK-rich regions of the blend membranes lack the high selectivity of PFSA, thus reducing the ionic conductivity. This is especially clear in the multi-layer membranes with accumulated SPEEK in the intermediate layer in the through-plane direction. Following initial property comparisons, thinner wire-electrospun SPEEK membranes were prepared with area resistance in the PFSA-comparable range. Among the wire-electrospun SPEEK/PFSA/PVDF membranes, the single-layered membrane with 8 wt% SPEEK (SPF1-8; 62 μm) displayed stable HBFB performance at 200 mA cm⁻² over 100 cycles (64 cm² active area). Based on the ex-situ measurements and cell performance results, a total of ∼10.5 wt% SPEEK is suggested as the limit for both single and multi-layered wire-electrospun membranes, combined with a maximum membrane thickness of ∼50 μm. This ensures robust HBFB performance, positioning wire-electrospun SPEEK/PFSA/PVDF membranes as a PFSA alternative in energy storage.

Abstract

A main component of a hydrogen-bromine flow battery (HBFB) is the ion exchange membrane. Available membranes have a trade-off between the major requirements: high proton conductivity, low bromine species crossover, and high mechanical and chemical stability. To overcome this, electrospinning of a highly proton conductive polymer (short side chain perfluorosulfonic acid (SSC PFSA)) and a hydrophobic inert polymer (polyvinylidene fluoride (PVDF)) was used to electrospin composite polymer fiber mats. Piles of multiple mats were hot pressed resulting in dense ion exchange membranes. Membranes with three different SSC PFSA/PVDF ratios were prepared, characterized, and subjected to short and long term (1500 h) HBFB testing. The electrospun membranes have performances very comparable to those of commercial membranes. For the SSC PFSA/PVDF electrospun membrane, a higher SSC PFSA loading gives a higher membrane proton conductivity compared to a lower loading, but at the expense of a higher bromine species crossover. The SSC PFSA/PVDF (50/50 wt%) membrane shows a coulombic efficiency of 98%, a voltaic efficiency of 80% and an initial available capacity of 105 Ah L− 1 at a current density of 150 mA cm− 2, which equals that of the current benchmark long side chain PFSA membrane. This performance is constant over 200 cycles during 2 months of continuous HBFB operation.

Abstract

Reinforced proton exchange membrane (PEM) were developed to increase the mechanical strength of thin membranes (≤30 µm) for PEM fuel cell applications. In hydrogen-bromine flow batteries (HBFBs), Br₂ and Br^– crossover through the membrane may affect the lifetime of HBFBs as a result of dissolution or passivation of the platinum catalyst. One study suggested that the reinforcement reduces the bulk Br₂ and Br^– transport and x-y (in-plane) swelling [1].

Abstract

Elestor is a company with a clear purpose. We are developing and delivering solutions to one of the most important challenges of this century: storing renewable energy on a very large scale. The transition to renewable power is no longer a distant ambition. It is the chosen path for governments, industries, and communities worldwide.

The ability to rely on solar and wind as primary sources of energy depends on technologies that can balance their intermittent nature. We must capture the electricity generated during moments of abundance and make it available at any time of demand. Elestor exists to make this possible.

Founded in 2014, Elestor has steadily grown into one of Europe’s leading innovators in flow battery technology. Our solution, the hydrogen-iron flow battery, is designed with the principle of abundance at its heart.

We utilise materials that are readily available, safe to handle, and cost-effective to deploy. In doing so, we bring to market an energy storage system that is technically sound, scalable and able to meet the needs of future societies.

This eBook offers a journey into our purpose, our technology, and the impact we aim to achieve.

Abstract

The addition of bromine complexing agent (BCA) to bromine electrolyte is an accepted method to reduce bromine vapor pressure making bromine-based flow batteries inherently safer. It is well-known that the amine functional group of the BCAs interact with Nafionmembranes.The novelty of the current work is that it investigates how this interaction of BCA with the four different membrane chemistries impacts the membrane characteristics and performance of hydrogen bromine flowbatteries(HBFBs). The impact of BCA 13 on the system performance is determined by the membrane chemistry. Exposure of Nafion membranes to BCA leads to 60% higher cell resistance, and 55% lower cell power density at 0.5V at 50% state-of-charge(SOC). This decrease is caused by the strong interaction between the negatively charged sulfonic acid groups in the membrane and the positively charged BCA. Lower SOC, lower bromine concentration and a higher free BCA concentration is detrimental in the cell operation. The use of LC PFSA membranes in the presence of BCA ions should be avoided. while BCA in combination with grafted sulfonated polyvinylidene fluoride (SPVDF) or grafted sulfonated polyethylene (SPE) membranes promising HBFB results are obtained.

Abstract

In search for cheap, high capacity energy storage, hydrogen-bromine flow batteries (HBFBs) are emerging as strong contenders [1], however, the volatility of the electrolyte and the associated risks must be managed. Bromine complexing agents (BCAs) are used as additives to the electrolyte, which have the ability to capture Br-ions and Br₂ thus decreasing the bromine vapour pressure [1]. The BCA-HBr-Br₂ complex separates as a high density oily layer.

Abstract

Electricity storage is essential for the transition to sustainable energy sources. Hydrogen-bromine flow batteries (HBFBs) are promising cost-effective energy storage systems. In HBFBs, proton exchange membranes are required to separate the two reactive materials, enabling proton transport for charge balancing. In this paper, we present a comprehensive overview of the key properties and an experimental performance map of cation exchange membranes for HBFBs. Our study shows that membrane water uptake is an important property due to its strong correlation with membrane resistance and bromide species crossover. Long chain perfluorosulfonic acid (LC PFSA) membranes are shown to have a better power density–crossover tradeoff and a higher stability than other types of functionalized membranes. The good power density-crossover tradeoff of LC PFSA membranes is the result of the high level of separation of hydrophobic and hydrophilic domains in the membrane, leading to well-connected ionic pathways for proton transport. Reinforcement of long chain LC PFSA membranes further improves their tradeoff because it mechanically constrains the swelling (lower water uptake), resulting in a lower crossover but a similar peak power density. Consequently, reinforced LC PFSA membranes are the most promising option for HBFBs.

Abstract

In a hydrogen-bromine flow battery (FB), the membrane characteristics determine the intrinsic resistance and crossover rate of bromide species and water. The crossover issue (from the bromine side to the hydrogen side) affects the performance and lifetime of hydrogen-bromine FBs because the bromide species deactivate the platinum catalyst and the liquid floods the electrode, which makes it inaccessible for the hydrogen [1].