UCSC team develops high-performance nanostructured composite catalyst for water-splitting to produce hydrogen
A low-cost, nanostructured composite material developed by researchers at UC Santa Cruz has shown performance comparable to Pt/C as a catalyst for the electrochemical splitting of water to produce hydrogen. An efficient, low-cost catalyst is essential for realizing the promise of hydrogen as a clean, environmentally friendly fuel.
Researchers led by Shaowei Chen, professor of chemistry and biochemistry at UC Santa Cruz, incorporated ruthenium ions into graphitic carbon nitride/reduced graphene oxide (rGO) hybrids to form Ru−C3N4/rGO composites. They found that the incorporation of Ru ions, at a loading of 1.93 at. %, leads to electron redistribution within the materials and significantly enhanced the hydrogen evolution reaction (HER) performance over those of other carbon-based electrocatalysts (C3N4, C3N4/rGO, and Ru−C3N4, with an overpotential of only −80 mV to reach a current density of 10 mA cm−2, a Tafel slope of 55 mV dec−1, and an exchange current density of 0.462 mA cm−2. This performance is comparable to that of Pt/C.
Mechanistically, effective electrocatalysts are required to achieve a high hydrogen generation rate as hydrogen evolution reaction (HER) involves multiple electron-transfer steps. Thus far, platinum-based materials supported on carbon exhibit the best electrocatalytic performance for HER; yet wide-spread commercial applications are hindered by the low natural abundance and high costs of platinum. In recent years, a variety of transition metal-based materials have been found to show apparent electrocatalytic activities towards HER. However, durability remains an issue because of corrosion of the catalysts in acid electrolytes, a common medium for HER. Carbon-based materials (such as graphene, carbon nanotubes, and amorphous carbon) have also been explored as viable catalysts for HER. Yet, thus far the activity has remained markedly lower than that of state-of-the art Pt/C.—Peng et al.
In the new composite material developed by Chen’s lab, the ruthenium ions embedded in the carbon nitride nanosheets change the distribution of electrons in the matrix, creating more active sites for the binding of protons to generate hydrogen. Adding graphene to the structure further enhances the redistribution of electrons.
The remarkable performance was accounted for by electron redistribution upon the incorporation of ruthenium ions into the C3N4-rGO composites, which led to efficient narrowing of the material bandgap, enhanced electric conductivity and charge carrier density, increasing number of active sites and reduced charge-transfer resistance. Such synergistic interactions among the structural components (C3N4, rGO, and Ru ions) highlight an effective strategy in the rational design and engineering of functional composites in the development of high-performance HER electrocatalysts.—Peng et al.
Despite electrocatalytic performance comparable to that of commercial platinum catalysts, researchers still have a long way to go to achieve cheap and efficient hydrogen production, Chen noted.
Y. Peng, W. Pan, N. Wang, J.-E. Lu, S. Chen (2018) “Ruthenium Ion‐Complexed Graphitic Carbon Nitride Nanosheets Supported on Reduced Graphene Oxide as High‐Performance Catalysts for Electrochemical Hydrogen Evolution” ChemSusChem 11, 130 doi: 10.1002/cssc.201701880