Flexible hydrogen fuel cell fabricated on paper with embedded aluminium foil

Direct hydrogen fuel cells are generally heavy and rigid systems based on metal or plastic materials, which are not suitable for various miniwatt and flexible devices. In this study, we have developed a lightweight and flexible fuel cell based on paper substrate embedded with an Al foil inside, which is used as an in-situ hydrogen source by reaction with an electrolyte solution during operation. Benefited from the inhibited hydroxyl transportation by the porous cellulose network, the vigorous Al corrosion reaction is well controlled even though strong alkaline electrolyte is adopted, so that the fuel cell can be discharged for more than 5 hours at 1 mA cm-2 (0.83 V) with only 3.5 mg Al foil. The corresponding faradaic and energy efficiencies are as high as 72% and 18.3%, respectively. The fuel cell flexibility is also quite good when facing different bending angles. Considering its moderate power output, this flexible paper-based hydrogen fuel cell is especially suitable for powering various miniwatt and flexible devices, such as wearable electronics, biosensors, RFID tags, etc. However, higher power can be obtained by suitable stacking of the fuel cell

Aluminum-air battery with cotton substrate: Controlling the discharge capacity by electrolyte pre-deposition

Conventional Al-air battery has many disadvantages for miniwatt applications, such as the complex water management, bulky electrolyte storage and potential leakage hazard. Moreover, the self-corrosion of Al anode continues even when the electrolyte flow is stopped, leading to great Al waste. To tackle these issues, an innovative cotton-based aluminum-air battery is developed in this study. Instead of flowing alkaline solution, cotton substrate pre-deposited with solid alkaline is used, together with a small water reservoir to continuously wet the cotton and dissolve the alkaline in-situ. In this manner, the battery can be mechanically recharged by replacing the cotton substrate and refilling the water reservoir, while the thick aluminum anode can be reused for tens of times until complete consumption. The cotton substrate shows excellent ability for the storage and transportation of alkaline electrolyte, leading to a high peak power density of 73 mW cm−2 and a high specific energy of 930 mW h g−1. Moreover, the battery discharge capacity is found to be linear to the loading of pre-deposited alkaline, so that it can be precisely controlled according to the mission profile to avoid Al waste. Finally, a two-cell battery pack with common water reservoir is developed, which can provide a voltage of 2.7 V and a power output of 223.8 mW. With further scaling-up and stacking, this cotton-based Al-air battery system with low cost and high energy density is very promising for recharging miniwatt electronics in the outdoor environment

High-performance aqueous Na–Zn hybrid ion battery boosted by “water-in-gel” electrolyte

Aqueous hybrid Na–Zn ion batteries (ASZIBs) are promising for large-scale energy storage due to their low cost and potential for high output voltage. However, most ASZIBs show limited discharge voltage (–1) due to inefficient usage of the dual ions. In this study, a novel large-electrochemical-window “water-in-gel” electrolyte based CuHCF-CNT/Zn Na–Zn hybrid battery is proposed, which achieves a high extraction voltage of Na ion (2.1 V vs Zn/Zn2+), together with a large discharge specific capacity (260 mAh g–1) thanks to the Zn-ion insertion, delivering a superior energy density of 440 Wh kg–1. The hybrid battery also shows a high capacity retention of 96.8% after 450 cycles. Moreover, an ultrahigh discharge capacity of 1250 mAh g–1 is achieved when further coupled with the Zn-O2 reaction, delivering the promising application of ion intercalation and metal–air hybrid battery

High-energy SWCNT cathode for aqueous Al-ion battery boosted by multi-ion intercalation chemistry

The aqueous Al-ion battery has achieved great progress in recent years. It now shows comparable performance to that of even non-aqueous Al-ion batteries. However, it also shows relatively low energy output and there is limited general understanding of the mechanism behind this restriction to its practical application. Thus, the development of a high-performance cathode material is in great demand. Herein, a high-capacity single-walled carbon nanotube (SWCNT) is developed as a cathode for the water-in-salt electrolyte-based aqueous Al-ion battery, which provides an ultra-high specific capacity of 790 mAh g–1 (based on the mass of SWCNT) at a high current density of 5 A g–1 even after 1000 cycles. Moreover, the SWCNT/Al battery shows a complicated multi-ion intercalation mechanism, where AlCl4–, Cl–, Al3+, and H+ can function at the same time, improving the battery output. Beyond recently revealed H+ and metal ion co-intercalation, the Cl-assisted intercalation of Al3+ ions mechanism is also studied by experimental characterization and modeling for the first time, which significantly boosts the Al3+ storage capacity. This multi-ion intercalation mechanism combines the high-voltage anion deintercalation and the high-capacity cation intercalation, and thus, benefits the development and application of high-energy Al-ion batteries in the future