waste electrical and electronic equipment (WEEE) generated after their disposal. The large quantities of WEEE and the wide variety of materials they often contain (ferrous metals, nonferrous metals, noblemetal, chemicals, glass, and plastics) have raised a serious alarm on their potential adverse health and environmental consequences when incorrectly disposed of. Moreover, this waste can be regarded as a resource of valuable materials (e.g., Au, Pt, Li) that if not recovered, has to be extracted again, resulting in natural resource depletion and environmental degradation. Recovering these metals and satisfying the demand for cheap secondhand equipment has become profitable business in emerging economies, which has turned Asia (in particular, China and India) and Africa into recipients of 90% of globally exported WEEE. [1] However, dismantling procedures are often carried out in inappropriate infrastructures with discarded components being openly incinerated and disposed of in unlined landfills that lack monitoring of leachate recovery systems of any kind. Due to their content of heavy metals, batteries are one of the most hazardous components of e-waste. For this reason, many Organization of Economic Cooperation and Development (OECD) countries have established regulations on the maximum permitted content of certain metals such as mercury or cadmium and the mandatory recycling of spent batteries. [2] Lithium-ion batteries are today the most predominant energy sources in portable applications because of their high energy density, low sensitivity to temperature variations, and no memory effect when recharging. [3] However, they are starting to raise important concerns related to the relatively low abundance of lithium metal-which is likely to increase the environmental impact of its extraction methods-and the large amount of CO 2 generated during battery manufacturing. In fact, its life cycle assessment determines that the use of lithium is only justified in rechargeable applications beyond hundreds of cycles, which clearly prohibits its use as primary batteries. [3,4] Despite all these worrying facts, battery recycling is far from meeting the goals set in developed regions (less than 30% of sold batteries are collected for proper recycling) and it is practically inexistent in low resource settings. [5] The most alarming issue is that consumption of batteries is expected to rise significantly in the following years due to the growth of small-sized portable appliances in the Information and Communications Technology This article presents a new approach for environmentally benign, low-cost batteries intended for single-use applications. The proposed battery is designed and fabricated using exclusively organic materials such as cellulose, carbon, and wax and features an integrated quinone-based redox chemistry to generate electricity within a compact form factor. This primary capillary flow battery is activated by the addition of a liquid sample and has shown continuous operation up to 100 min with an output voltage ...

Electrochemical energy conversion is an important supplement for storage and on-demand use of renewable energy. In this regard, microfluidics offers prospects to raise the efficiency and rate of electrochemical energy conversion through enhanced mass transport, flexible cell design, and ability to eliminate the physical ion-exchange membrane, an essential yet costly element in conventional electrochemical cells. Since the 2002 invention of the microfluidic fuel cell, the research field of microfluidics for electrochemical energy conversion has expanded into a great variety of cell designs, fabrication techniques, and device functions with a wide range of utility and applications. The present review aims to comprehensively synthesize the best practices in this field over the past 20 years. The underlying fundamentals and research methods are first summarized, followed by a complete assessment of all research contributions wherein microfluidics was proactively utilized to facilitate energy conversion in conjunction with electrochemical cells, such as fuel cells, flow batteries, electrolysis cells, hybrid cells, and photoelectrochemical cells. Moreover, emerging technologies and analytical tools enabled by microfluidics are also discussed. Lastly, opportunities for future research directions and technology advances are proposed.

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Glycerol/bleach flow-through microfluidic fuel cells are presented. Carbon paper-modified Pt/C nanoparticles were used as the anode and cathode. Glycerol oxidation in alkaline medium was tested against hypochlorite reduction in alkaline and acidic media. The mixed media system displayed a power density of 315 mW cm and an open circuit voltage of 1.9-2.0 V.

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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...