This study benchmarks cycle performance of electrolyte solutions containing novel bromine sequestration agents (BSA) in a zinc bromine flow battery.

Six ionic liquids were assessed for their suitability as alternative bromine-sequestering agents (BSAs) in zinc/bromine redox flow batteries (Zn/Br RFBs) via comparison against conventional BSA, 1-ethyl-1-methylpyrrolidinium bromide ([C2MPyrr]Br).

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Five supporting electrolytes were studied for their viability as alternatives in the zinc half-cell of a zinc/bromine (Zn/Br) flow battery. The secondary electrolytes studied included sodium salts of the following anions: Br -, SO 4 2-, H 2 PO 4 -and NO 3 -, which were compared against the conventionally employed Cl -. Cyclic voltammetry and Tafel analysis showed improved electrochemical performance from electrolytes containing NaBr, Na 2 SO 4 and NaH 2 PO 4 . Consequently, these chemicals are proposed as potential alternatives in future Zn/Br design work. Electrochemical impedance spectroscopy revealed that the lowering of charge-transfer resistance and diffusion limitation was the contributing reason toward improved performance from those electrolytes. Scanning electron microscopy and X-ray diffraction of zinc electrodeposits obtained during charging showed the type of supporting electrolyte present alters zinc crystallinity. Generation of smaller crystals was related to observations of good half-cell performance during voltammetry. Mossy deposits were linked with higher nucleation overpotentials between zinc plating/de-plating. The well-performing Na 2 SO 4 supporting electrolyte produced mossy deposits, suggesting that contrary to common assumption, such deposition behavior is possibly unrelated to poor zinc-side performance. While the proposed compounds are intended for Zn/Br flow battery applications, they are possibly adaptable to other types of flow batteries utilizing the Zn 2+ /Zn redox couple. Flow batteries are an attractive option for storing electricity at the utility-scale, offering benefits such as the increased uptake of intermittent renewable power sources such as solar and wind.1-8 Zinc/bromine redox flow batteries (Zn/Br RFBs) are a viable candidate for such applications due to factors such as a high theoretical specific energy (440 Wh kg -1 ) 9,10 and relatively low cost of the materials of construction. Consequently, it is of commercial, environmental and social interest to pursue materials research leading to improved performance of such systems.During the charging phase of the Zn/Br battery, the following reactions occur within the zinc and bromine half-cells, respectively (Eqs. 1-2):The reverse occurs during the discharge phase, whereby the primary electrolyte (i.e. ZnBr 2 ) is regenerated. The Zn/Br electrolyte also contains a bromine sequestration agent which complexes with Br 2 evolved at the positive electrode to form a separate phase which is immiscible with the aqueous electrolyte. Organic quaternary ammonium bromides such as 1-ethyl-1-methylpyrrolidinium bromide are commonly employed as sequestration agents. 11,12Dendrite formation during the charging phase has long been a major observation and source of concern during the design of RFBs which employ zinc electrodeposition, with various strategies employed to minimize this issue. [13][14][15][16] Dendrites increase operational risks by causing problems such as short circuiting of cells. It is also beneficial to promote efficient e...

This study presents a life cycle analysis (LCA) of end-of-life (EoL) photovoltaic (PV) systems in Australia. Three different EoL scenarios are considered for 1 kWh of electricity generation across a 30-year PV system lifespan: (i) disposal to landfill, (ii) recycling by laminated glass recycling facility (LGRF), and (iii) recycling by full recovery of EoL photovoltaics (FRELP). It is found that recycling technologies reduce the overall impact score of the cradle-to-grave PV systems from 0.00706 to 0.00657 (for LGRF) and 0.00523 (for FRELP), as measured using the LCA ReCiPe endpoint single score. The CO2 emissions to air decrease slightly from 0.059 kg CO2 per kWh (landfill) to 0.054 kg CO2 per kWh (for LGRF) and 0.046 kg CO2 per kWh (for FRELP). Increasing the PV system lifespan from 30 years to 50 and 100 years (a hypothetical scenario) improves the ReCiPe endpoint single-score impact from 0.00706 to 0.00424 and 0.00212, respectively, with corresponding CO2 emissions reductions from 0.059 kg CO2 per kWh to 0.035 and 0.018 kg CO2 per kWh, respectively. These results show that employing recycling slightly reduces the environmental impact of the EoL PV systems. It is, however, noted that recycling scenarios do not consider the recycling plant construction step due to a lack of data on these emerging PV panel recycling plants. Accounting for the latter will increase the environmental impact of the recycling scenarios, possibly defeating the purpose of recycling. Increasing the lifespan of the PV systems increases the longevity of the use of panel materials and is therefore favorable towards reducing environmental impacts. Our findings strongly suggest that PV recycling steps and technologies be carefully considered before implementation. More significantly, it is imperative to consider the circular design step up front, where PV systems are designed via circular economy principles such as utility and longevity and are rolled out through circular business models.

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Zinc/bromine flow batteries are a promising solution for utility-scale electrical energy storage. The behavior of complex Zn–halogen species in the electrolyte during charge and discharge is currently not well-understood, and is an important aspect to be addressed in order to facilitate future electrolyte formulations. The speciation of the primary zinc bromide electrolyte with and without a secondary zinc chloride electrolyte is studied in the present work. Raman spectroscopy was carried out on aqueous solutions of zinc bromide at 5 concentrations (2–4 M) to account for the initial and later stages of charging, with 3 concentrations (1–2 M) of zinc chloride. Mixed solutions containing various combinations of each primary and secondary electrolyte concentrations were also studied. Semi-quantitative analysis of peaks after Gaussian and Lorentzian peak deconvolution showed that the proportion of four-ligand coordinated Zn–halides (i.e. [ZnBr4]2− and [ZnCl4]2−) increases with higher salt concentration, as compared to complexes with lower halide coordination numbers. The presence of a previously unassigned peak was observed at the 220 cm−1 band in the Raman spectra of mixed electrolytes. Results from ab-initio molecular modeling using the GAUSSIAN 16 software package suggests this peak is due to the presence of the hybrid-halide anionic complex [ZnBr2Cl(H2O)]–. Increasing the Cl:Br ratio in electrolytes promotes hybridization and subsequently decreasing the proportion of single-halide Zn–Br complexes. While this speciation study is focused on Zn/Br batteries, the findings are also potentially applicable to other energy storage and electrochemical systems containing zinc halide electrolytes.