CityUHK JC STEM Lab Of Circular Bio-Economy Showcases Research Milestones: Developing Smart Building Skins And Eco-Friendly Hydrogen Production Technology

The JC STEM Lab of Circular Bio-economy (the Lab) at City University of Hong Kong (CityUHK) has recently achieved a breakthrough in the field of sustainable development technologies. A research team led by Professor Lee Duu-Jong, Director of the Lab and Professor in the Department of Mechanical Engineering, has successfully developed a bio-inspired "all-weather building skin" that cools in sunlight and harvests energy from rain, alongside a "turbocharged" solar hydrogen system powered by low-cost copper ions. These innovations provide a transformative pathway for urban energy conservation and clean energy production, reinforcing the Lab's commitment to translating cutting-edge research into tangible social benefits.

Under Professor Lee’s leadership, the Lab is dedicated to shifting the traditional linear "take–make–dispose" model into a circular bioeconomy framework. "The core of a circular bio-economy lies in creating 'closed-loop' systems that enable continuous recycling of resources throughout the production and consumption cycle," said Professor Lee.

Inspired by the layered leaf structure of the Tillandsia air plant, Zeng Yijun, a PhD student of the Department of Mechanical Engineering (MNE), developed "BRIDGE skin", a paintable, all-weather building coating. This technology enables building envelopes—including roofs and walls — to harness free natural resources to achieve both energy savings and electricity generation under changing weather conditions.

In sunny conditions, the coating reflects over 95% of solar energy and emits stored heat as infrared radiation into space. This reduces surface temperatures by up to 9.5°C below ambient levels, significantly reducing air-conditioning electricity demand.

During rainfall, the impact of water droplets triggers electrical pulses. This energy is sufficient to power small liquid-crystal displays (LCDs) or wireless sensors directly.

Traditionally, integrating electrodes and energy-harvesting layers often compromises a material’s ability to reflect sunlight and radiate heat. Inspired by the stratified structure of Tillandsia air plants, the team overcame this limitation. By adopting a stratified design, the outer layer manages droplet contact, accelerating water movement and self-cleaning, while the buried layers are responsible for sunlight reflection, heat dissipation, and charge storage, ensuring maximum efficiency without trade-offs.

Additionally, the paintable nature of the coating makes it significantly easier to apply to existing building retrofits than traditional rigid power-generating devices, demonstrating immense practical value.

Another breakthrough is the closed-loop, round-the-clock, eco-friendly hydrogen production system, developed by postdoctoral fellow Dr Mak Chun Hong from MNE. Conventional hydrogen production processes currently rely heavily on costly and rare metals such as platinum, making large-scale production difficult. The research team successfully replaced platinum with abundant, price-stable, low-cost copper ions. This has unlocked a highly efficient dynamic chemical reaction that can generate hydrogen even under a smartphone's flashlight.

The system introduces copper ions to create a self-regenerating cycle, enabling continuous hydrogen production while recycling its own chemical waste. The key lies in capturing a temporary "copper hydride" state, allowing it to store energy under light and continue releasing hydrogen in the dark, achieving round-the-clock green fuel production.

Professor Lee likened this system to a "chemical turbocharger" that uses copper as a kinetic booster. This breakthrough paves the way for the mass production of affordable, scalable, round-the-clock zero-emission fuel.

These cost-effective, self-sustaining technologies will provide a critical clean energy buffer for Hong Kong and the Greater Bay Area, enhancing resilience against global energy market volatility. Professor Lee emphasised that the Lab is dedicated to developing key technologies that promote resource circularity within high-density urban environments, maximising the utility of architectural spaces.

“The JC STEM Lab of Circular Bio-economy will continue to drive the translation of research findings into practical applications," Professor Lee stated. "Through research-academic-industrial collaboration, we aim to establish industrial alliances that leverage CityUHK’s research strengths to develop low-carbon, circular smart cities, directly supporting the nation’s 15th Five-Year Plan and the carbon neutrality goals of Hong Kong’s Climate Action Plan 2050."