Awardee: Ir Prof Feng Shien Ping

Low-grade heat is abundantly available in the form of waste heat or in the environment. For example, in the process of converting primary energy into useful energy, over 60% is discharged to the environment in the form of waste heat. This involves a vast amount of low-grade heat below 100^oC. This unavoidable by-product of doing work has been an overlooked renewable energy. Low-grade heat recovery can significantly reduce greenhouse gas emissions and bring tangible economic and environmental benefits. However, its efficient recovery still presents a great challenge.

An innovative electrochemical cell for low-grade heat recovery

Our team invented a new electrochemical system named Direct Thermal Charging Cell (DTCC) for efficient conversion of low-grade heat to electricity. This is at the forefront of performance compared with existing technologies in the low-grade heat regime. The system uses asymmetric electrodes of graphene oxide (GO)/Pt nanoparticles cathode and polyaniline anode (PANI) in aqueous Fe²⁺/Fe³⁺ redox electrolyte for efficient conversion of low-grade heat to electricity (Figure 1). Continuous energy conversion is achieved under isothermal heating throughout the charge and discharge process. The system can be self-regenerated when cooled down, thus allowing device cyclability. This system is the first demonstration of heat-to-electricity conversion under isothermal heating and chemical regeneration, which revolutionises the design of thermoelectrochemical systems. Such technology is fundamentally different from the state-of-the-art technologies with power generation coupled to temperature differential. DTCCs have unique advantages for practical application, including low cost, bendable nature, technical simplicity and ability to form stacks of cells. Additionally, it is a simple system with basic unit size of only 1.5 cm² and thickness of 1 mm to 1.5 mm.

Figure 1: (A) Schematic diagram of DTCC consisting of GO/PtNPs cathode and PANI anode (with carbon paper (CP) current collector) in Fe²⁺/Fe³⁺ redox electrolyte; (B) DTCC pouch cell; and (C) DTCC module

Startup company and commercialisation

Through this patented technology, a start-up called High Performance Solution Ltd. (HPS) was established and supported by the Technology Start-up Support Scheme for Universities (TSSSU) for three consecutive years. HPS was selected to enter the Incu-Tech three-year programme at the Hong Kong Science Park and has received its first revenue from the prototypes. Currently, the team is collaborating with industrial partners to produce integrated prototypes with DTCC modules for recycling low-grade heat in various applications such as air conditioners and smart windows, with the aim of demonstrating the feasibility of commercialisation (Figure 2).

Figure 2: Product development. (A) Integration of DTCCs with HVAC system for recycling low-grade heat from the compressor and condenser into electricity; and (B) Integration of DTCCs in the window frame to harvest solar heat for powering electrochromic windows

Our contribution

The invented DTCC is a green technology with advantages of flexibility, cost-effectiveness and scalability, making it promising for practical applications in direct energy conversion from low-grade heat sources. This new technology is expected to open new horizons for many applications and promises to become disruptive in the marketplace for the thermoelectric community.