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The emergence of on-skin electronics with functions in human−machine interfaces and on-body sensing calls for the development of smart flexible batteries with high performance. Electrochromic energy-storage devices provide a visual indication of the capacity through a real-time change in color without any additional power supply. In this study, dual-function battery and supercapacitor devices for skininterfaced wearable electronics are developed by a simple and scalable transfer printing method, featuring a thickness of less than 50 μm. Supercapacitive and battery-type devices with areal capacities of 113.4 mF cm −2 and 6.1 μAh cm −2 , respectively, are achieved by assembling electrochromic cathodes, hydrogel film electrolyte, and zinc anode. The high flexibility of the ultrathin energy devices endows them with good conformity on arbitrarily shaped surfaces, including elastic human skin, further enhancing the capability of intrinsically non-stretchable thin-film electronics. Our results provide a pathway for the development of versatile electronic skins and next-generation wearable electronics.

Supercritical CO2 (S-CO2) power-cycle systems are a promising technology for waste-heat recovery from internal combustion engines (ICEs). However, the effective utilisation of the heat from both the exhaust gases and cooling circuit by a standalone S-CO2 cycle system remains a challenge due to the unmatched thermal load of these heat sources, while a large amount of unexploited heat is directly rejected in the system's pre-cooler. In this paper, a combined-cycle system for ICE waste-heat recovery is presented that couples an S-CO2 cycle to a bottoming organic Rankine cycle (ORC), which recovers heat rejected from the S-CO2 cycle system, as well as thermal energy available from the jacket-water and exhaust-gas streams that have not been utilised by the S-CO2 cycle system. Parametric optimisation is implemented to determine operating conditions for both cycles from thermodynamic and economic perspectives. With a baseline case using a standalone S-CO2 cycle system for an ICE with a rated power output of 1170 kW, our investigation reveals that the combined-cycle system can deliver a maximum net power output of 215 kW at a minimum specific investment cost (SIC) of 4670 $/kW, which are 58% and 4% higher than those of the standalone S-CO2 cycle system, respectively. A range of ICEs of different sizes are also considered, with significant performance improvements indicating a promising potential of exploiting such combined-cycle systems. This work motivates the pursuit of further performance improvements to waste-heat recovery systems from ICEs and other similar applications.