Sunlight and sugarcane waste power hydrogen production at rate four times higher than commercialization benchmark

A technology for hydrogen (H₂) production has been developed by a team of researchers led by Professors Seungho Cho and Kwanyong Seo from the School of Energy and Chemical Engineering at UNIST, in collaboration with Professor Ji-Wook Jang’s team from the Department of Materials Science and Engineering at UNIST.

Their research is published in the journal Nature Communications.

This innovative method utilizes biomass derived from sugarcane waste and silicon photoelectrodes to generate H₂ exclusively using sunlight, achieving a production rate four times higher than the commercialization benchmark set by the U.S. Department of Energy (DOE).

H₂ is recognized as a next-generation fuel since it emits no greenhouse gases when burned and stores energy at a density 2.7 times greater than gasoline. Despite this, the majority of H₂ produced today is derived from natural gas, a process that generates substantial carbon dioxide emissions.

The research team has developed a photoelectrochemical (PEC) H₂ production system that facilitates H₂ production without carbon dioxide (CO₂) emissions by utilizing furfural extracted from sugarcane waste.

In this system, furfural is oxidized at the copper electrode to produce H₂, with the residual material converting into furoic acid, a high-value product.

H₂ is produced at both electrodes in this system. At the opposing silicon photoelectrode, water is also split to yield H₂. This dual production mechanism theoretically doubles the production rate compared to conventional PEC systems, with the actual performance reaching 1.4 mmol/cm²·h, nearly four times the U.S. Department of Energy’s target of 0.36 mmol/cm²·h.

The H₂ production process begins when the photoelectrode absorbs sunlight and generates electrons. Crystalline silicon photoelectrodes are advantageous for H₂ production due to their capacity to generate a significant number of electrons. However, the low voltage generated (0.6 V) makes it challenging to initiate H₂ production reactions without external power.

The research team addressed this issue by introducing the oxidation reaction of furfural on the opposing electrode to balance the system’s voltage.

This approach preserves the high photocurrent density characteristic of crystalline silicon photoelectrodes while alleviating the voltage burden on the entire system, enabling H₂ production without the need for external power. Photocurrent density refers to the flow of electrons per unit area and is directly linked to H₂ production rates.

Additionally, this system employs an interdigitated back contact (IBC) structure to minimize voltage losses within the photoelectrode and wraps the electrode in nickel foil and glass layers to protect it from the electrolyte, ensuring long-term stability.

The submerged structure of the silicon photoelectrode provides a self-cooling effect, demonstrating superior efficiency and stability compared to external coupling structures, where the battery generating electricity through water decomposition and the electrolyzer producing H₂ are separate entities.

Professor Jang stated, “This technology achieves an H₂ production rate from solar energy that is four times higher than the commercialization standard set by the U.S. Department of Energy, playing a crucial role in enhancing the economic viability of solar H₂ and ensuring competitive pricing against fossil fuel-based H₂.”