Evaluation of Redox Chemistries for Single-Use Biodegradable Capillary Flow Batteries

Abstract

The rate of battery waste generation is rising dramatically worldwide due to increased use and consumption of electronic devices. A new class of portable and biodegradable capillary flow batteries was recently introduced as a solution for single-use disposable applications. The concept utilizes stored organic redox species and supporting electrolytes inside a dormant capillary flow cell which is activated by the dropwise addition of aqueous liquid. Herein, various organic redox species are systematically evaluated for prospective use in disposable capillary flow cells with regards to their electrochemical characteristics, solubility, storability and biodegradability. Qualitative ex-situ techniques are first applied to assess half-cell solubility, redox potential and kinetics, followed by quantitative in-situ measurements of discharge performance of selected redox chemistries in a microfluidic cell with flow-through porous electrodes. Para-benzoquinone in oxalic acid and either hydroquinone sulfonic acid or ascorbic acid in potassium hydroxide are identified for the positive and negative half-cells, respectively, yielding a maximum discharge power density of 50 mW/cm 2 . A prototype capillary flow battery using the same redox chemistries demonstrates robust cell voltages above 1.0 V and maximum discharge power of 1.9 mW. These results show that practical primary battery performance can be achieved with biodegradable chemistries in a disposable device. The market demand for small-size single-use electronic devices such as portable sensors and diagnostic devices has been rising drastically in recent years. The power needs of such devices have so far been met by Li-ion batteries and other primary battery technologies, resulting in a consequent rise in their consumption. These batteries often contain heavy metals and strong electrolytes which make them one of the most hazardous components of electronic waste.1 In addition, the majority of the primary Li batteries used globally are not recycled nor properly disposed of, thus ending up in landfills without regulations.2 In applications that do not require long discharge times and have modest capacity requirements such as medical devices, these batteries are not even fully discharged before being disposed of. This requires further resources for re-extracting the materials if not recovered, which is not sustainable and raises concerns about the abundance of these resources. The end-of-life fate of these batteries and their life cycle assessment therefore only justifies the use in rechargeable applications beyond hundreds of cycles.3,4 These issues trigger a worrying concern about associated future environmental hazards from the battery waste generation and urgently call for novel alternatives, tightened environmental policies and switching the linear consumption habit of "take-make-dispose" for these primary batteries into a circular economy model. This approach utilizes novel concepts such as green electronics and cradle-to-cradle design to eliminate waste from the conc...

An Organic Redox Flow Cell‐Inspired Paper‐Based Primary Battery

“…As in membrane‐less microfluidic co‐laminar flow cells, this capillary flow cell facilitates operation under mixed‐media conditions, in which an alkaline negative electrode and an acidic positive electrode are employed. This feature enables higher electrochemical cell voltages during discharge operation and the utilization of a wider range of available species and electrolytes . Additionally, mixed‐media operation provides the advantage of a neutral or near neutral pH as the acidic and alkaline neutralize at the absorbent pad, which allows a safe disposal after operation.…”

“…in 2014 and Ibrahim et al. in 2017, both of which used water‐based solutions of an anthraquinone as the negative electrode and benzoquinone as the positive one, yielding power densities of around 4 mW cm −2 with 0.6 V open circuit potential . Despite good performance, the vast majority of flow cells require external pumps to maintain the flow of reactants.…”

Biopolymer Electrolyte Membranes (BioPEMs) for Sustainable Primary Redox Batteries

“…[28,38] Thus, a dedicated setup was designed and four electroactive species were selected for the crossover test.…”

“…These species have been previously identified as benign and eco-friendly redox chemistries for biodegradable batteries. [28,38]…”

“…Polarization curves were performed in complete cell configuration with the two best performing BioPEMs and using the redox chemistries previously characterized (all-quinone and AA/Fe 3+ ). [28,38] These measurements were performed every 20 min for a 2 h period using the working electrodes of the SPEs as current collectors. The open circuit voltage of the cell was measured once the liquid species were added to both cell compartments and a steady values of 0.75 ± 0.05 V in all-quinone and 0.90 ± 0.05 V in AA/Fe 3+ were achieved.…”