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Al-air batteries are generally fabricated by rigid and heavyweight materials such as metal or plastic, meanwhile a bulky electrolyte solution either in static or circulation is requisite to ensure their steady operation. Therefore, they are less suitable for powering flexible and portable devices with lower power demand, such as wearable electronics, point-of-care test assays, RFID tags, etc. This work develops a flexible and lightweight Al-air battery with much less electrolyte storage, which is totally fabricated on a cellulose paper. The Al foil anode is embedded inside the paper substrate during paper-making process, while the air-breathing cathode is deposited onto the paper surface using an oxygen reduction ink. Despite its simple structure and low cost, this flexible Al-air battery can deliver a satisfactory power density of 19 mW cm−2 with alkaline electrolyte, and its operation lifespan is as long as 58 h with only 25 mg Al when saline electrolyte is employed. The corresponding Al specific capacity is as high as 2338 mA h g−1. In addition, this battery exhibits an excellent flexibility when facing different bending angles from 60 to 180° and multiple bending times greater than 1000. Furthermore, a flexible current or voltage output can be easily obtained by scaling up or stacking the present flexible Al-air battery, respectively, and the corresponding stacking efficiency is as high as 94%. In the future, non-metal oxygen catalyst will be employed to improve its environmental friendliness, and hot-pressing will be adopted to further increase its robustness to external deformation. • A flexible Al-air battery is developed for powering flexible and portable devices. • Al anode is embedded inside the paper, while ink cathode is deposited on the paper. • Peak power density of 19 mW cm−2 and specific capacity of 2338 mA h g−1 is obtained. • Battery performance is very stable even it is bended to 180° and by 1000 times. • Battery scaling-up and stacking is very convenient and highly-efficient (94%). [ABSTRACT FROM AUTHOR]

Paper microfluidics is used to produce single layer galvanic and hybrid cells to produce energy that could power paper-based analytical sensors. When two aqueous streams are absorbed onto paper to establish co-laminar flow, the streams stay in contact with each other with limited mixing. The interface at which mixing occurs acts as a charge-transfer region, eliminating the need for a salt bridge. We designed a Cu Zn galvanic cell that powers an LED when two are placed in series. We also used more powerful redox couples (formate and silver, formate and permanganate) to produce higher power density (18 and 3.1 mW mg −1 Pd). These power densities are greater than previously reported paper microfluidic fuel cells using formate or methanol. The single layer design is much more simplified than previous reports of multi-layer galvanic cells on paper. [ABSTRACT FROM AUTHOR]

With a view to ascertaining the optimum number of stand-by systems, this paper derives the expected cost function for operating n independent systems for a time period of length t, with s spare systems available. [ABSTRACT FROM AUTHOR]

We characterize an affordable method of producing stencils for submillimeter physical vapor deposition (PVD) by using paper and a benchtop laser cutter. Patterning electrodes or similar features on top of organic or biological substrates is generally not possible using standard photolithography. Shadow masks, traditionally made of silicon-based membranes, circumvent the need for aggressive solvents but suffer from high costs. Here, we evaluate shadow masks fabricated by CO2 laser processing from quantitative filter papers. Such papers are stiff and dimensionally stable, resilient in handling, and cut without melting or redeposition. Using two exemplary interdigitated electrode designs, we quantify the line resolution achievable with both high-quality and standard lenses, as well as the positional accuracy across multiple length scales. Additionally, we assess the gap between such laser-cut paper masks and a substrate, and quantify feature reproduction onto polycarbonate membranes. We find that ~100 µm line widths are achievable independent of lens type and that average positional accuracy is better than ±100 µm at 4"-wafer scale. Although this falls well short of the micron-size features achievable with typical shadow masks, resolution in the tenths to tens of millimeters is entirely sufficient for applications from contact pads to electrochemical cells, allowing new functionalities on fragile materials. [ABSTRACT FROM AUTHOR]

We investigated the electrochemical performance of reduced graphene oxide (rGO)/carbon nanotube (CNT) hybrid papers as binder-free anodes for potassium-ion batteries. RGO/CNT hybrid papers were fabricated by vacuum filtration and thermal reduction. The potassium-ion storage ability of rGO paper was significantly enhanced by CNT incorporation and the electrochemical performance of the hybrid papers was related to the weight ratio of CNTs. The optimal rGO/CNT-30% paper can deliver an initial reversible discharge capacity of 351 and 223 mA h g−1 at a current density of 10 and 50 mA g−1, respectively. A capacity of 148 mA h g−1 was achieved after 200 cycles at a current density of 50 mA g−1. The enhanced performance of rGO/CNT hybrid papers is attributed to the formation of a 3D conductive carbon network, in which the graphene layers are bridged by CNTs. Such a structure could effectively facilitate the transport of electrons and potassium ions and provide more storage sites for potassium ions. Image 1 • RGO/CNT hybrid papers were fabricated by vacuum filtration and thermal reduction. • The potassium-ion storage ability of rGO paper was significantly enhanced by CNT incorporation. • RGO/CNT-30% paper delivered a reversible capacity of 232 mA h g−1 at a current density of 50 mA g−1, respectively. • The enhanced performance of rGO/CNT hybrid papers was attributed to the formation of a 3D conductive carbon network. [ABSTRACT FROM AUTHOR]