Korean researchers have developed a long-lasting organic semiconductor photoelectrode with world-leading solar hydrogen production performance.
A joint research team led by Professor Kim Jin-young of the Graduate School of Carbon Neutrality at Ulsan National Institute of Science and Technology (UNIST) and Professor Woo Han-young of Korea University announced on the 26th that they developed a material enabling uniform and firm attachment of platinum catalysts to organic photoelectrodes, creating a long-lasting organic photoelectrode with hydrogen production performance comparable to inorganic photoelectrodes.
Solar hydrogen production is a technology that generates hydrogen by exposing photoelectrodes submerged in water to sunlight. When sunlight hits the semiconductor photoactive layer of the photoelectrode, electrons are generated, triggering a chemical reaction that produces hydrogen from water. Platinum catalysts coated on the surface lower the energy required for this chemical reaction.
Organic photoelectrodes using organic semiconductor photoactive layers have faced problems with platinum catalysts not being evenly applied or easily detaching during hydrogen production reactions. This has been one of the main reasons why commercialization has been difficult despite the advantages of low production costs and lightweight, flexible properties.
The joint research team created a high-efficiency, durable organic photoelectrode by coating the photoactive layer with a self-developed multifunctional special polymer (PNDI-NI). Unlike typical hydrophobic polymers used in organic photoelectrodes, this special polymer possesses both hydrophobic and hydrophilic characteristics, allowing platinum catalysts to form evenly on the surface. Platinum catalysts are applied as platinum ions dissolved in aqueous solution transform into solid form on the photoelectrode surface. However, because the photoactive layer is hydrophobic and repels aqueous solutions, achieving uniform platinum coating has been difficult. The hydrophilic portion of the developed special polymer compensates for this drawback.
In particular, iodine ions in the hydrophilic portion help platinum ions rapidly grow into solid platinum while also adsorbing platinum. This enables denser formation of platinum particles on the photoelectrode surface, with the resulting platinum catalysts firmly fixed to the surface, addressing durability issues.
Experimental results showed that organic photoelectrodes using this technology recorded a high photocurrent density of 17.69 mA cm⁻² under neutral electrolyte conditions, with applied bias photon-to-current efficiency (ABPE) reaching 8.88%. This represents world-leading performance among organic-based photoelectrodes and is comparable to inorganic photoelectrodes, which are generally considered more efficient than organic photoelectrodes.
Ha Jung-min and Shuran Xu of Korea University, along with Kim Jae-hyung, an integrated master's-doctoral program researcher at UNIST, participated as first authors in this research.
The joint research team stated, "From special polymer coating to platinum catalyst formation, all processes can be conducted in solution state, which is advantageous for large-area fabrication and can be extended to various catalyst materials beyond platinum and other organic photoelectrodes," adding, "We have established the technological foundation needed for application in industrial settings for solar hydrogen production that directly produces hydrogen from sunlight."
The research results were published in the international academic journal "Advanced Energy Materials" on January 6, with research funding provided by the National Research Foundation of Korea (NRF) under the Ministry of Science and ICT.