We are not talking about cracking open eggs and put them into hydrogen fuel cells (not even during Easter). Chemical researchers from the Osaka City University (OCU) have reported their innovative idea of producing carbon-free hydrogen using a photocatalytic matrix made of an egg white ingredient, lysozymes.
Even though hydrogen fuel cell is considered an ideal way to power vehicles due to zero carbon emission at the tailpipe, the current landscape of hydrogen production easily destroyed the "green" image of the technology. The majority of hydrogen is made from natural gas, only a small quantity by other routes such as biomass gasification or electrolysis of water. With millions of tonnes of CO2 generated from hydrogen production, fuel cell technology is nowhere to be close carbon-free.
Scientists have been working on boosting the efficiency and usability of water electrolysis. The hydrogen evolution reaction (HER, 2 H+ + 2 e−→ H2) is at the center of electrochemical water splitting. It is a classic example of a two-electron transfer reaction with one catalytic intermediate and offers the potential to free up H2.
Take a highly commercialized technique proton exchange membrane (PEM) electrolysis for example, it is comprised of a solid polymer membrane sandwiched by an anode (contains iridium catalyst) and a cathode (contains platinum catalyst). It uses water as a reactant and generates hydrogen and oxygen gas as products.
The OCU team’s focus is to develop a hydrogen generation platform that is powered by solar energy. To harness photonic energy to speed up the electrolysis of water, researchers looked into building a biological scaffold that can house photocatalytic component like platinum nanoparticles. The catalysts need to be distributed in a highly organized manner otherwise the catalytic reactions would not happen. Previous research has identified proteins from bacteria culture as a potential matrix, but the Japanese scientists turned to the lysozyme crystals from chicken eggs as a cheap and highly available alternative.
Lysozyme is an antimicrobial enzyme produced by animals to break down gram-positive bacterial cell wall. A large amount of lysozyme can be found in egg white. “Lysozyme crystals have a highly ordered nanostructure and, thus, we can manipulate the molecular components when they accumulate in the crystals,” said Hiroyasum Tabe a Research Associate with the OCU team.
To ensure there is no defect in the lysozyme’s structure, X-ray crystallography was used to examine this biological scaffold for the catalysts. This analysis is crucial for verifying the precise accumulation and immobilization (so no components shift position amid reactions). Rose bengal, a dye commonly used in eye drops, was applied to the crystals to identify potential damages. Results from X-ray analysis suggest that porous protein crystals are promising platforms to periodically and rationally accumulate catalytic components by using molecular interactions, according to Tabe.
This study is published in Applied Catalysis B this February.
Recent Development in Hydrogen Evolution Reaction Catalysts and Their Practical Implementation. Credit: ACS
Source: Osaka City University