In a study published March 9 in Nature Chemistry, University of Wisconsin-Madison chemistry Professor Kyoung-Shin Choi presents a new approach to combine solar energy conversion and biomass conversion, two important research areas for renewable energy.

 

For decades, scientists have been working to harness the energy from sunlight to drive chemical reactions to form fuels such as hydrogen, which provide a way to store solar energy for future use. Toward this end, many researchers have been working to develop functional, efficient and economical methods to split water into hydrogen, a clean fuel, and oxygen using photoelectrochemical solar cells (PECs). Although splitting water using an electrochemical cell requires an electrical energy input, a PEC can harness solar energy to drive the water-splitting reaction. A PEC requires a significantly reduced electrical energy input or no electrical energy at all.

 

In a typical hydrogen-producing PEC, water reduction at the cathode (producing hydrogen) is accompanied by water oxidation at the anode (producing oxygen). Although the purpose of the cell is not the production of oxygen, the anode reaction is necessary to complete the circuit.

 

Unfortunately, the rate of the water oxidation reaction is very slow, which limits the rate of the overall reaction and the efficiency of the solar-to-hydrogen conversion. Therefore, researchers are currently working to develop more efficient catalysts to facilitate the anode reaction.

 

Choi, along with postdoctoral researcher Hyun Gil Cha, chose to take a completely new approach to solve this problem. They developed a novel PEC setup with a new anode reaction. This anode reaction requires less energy and is faster than water oxidation while producing an industrially important chemical product. The anode reaction they employed in their study is the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). HMF is a key intermediate in biomass conversion that can be derived from cellulose - a type of cheap and abundant plant matter. FDCA is an important molecule for the production of polymers.