Electrochemical imaging shows that phosphorus and nitrogen atoms are vital for improving the potential of holey graphene to boost the liberation of hydrogen during electrolysis.
An international team of researchers has enhanced the potential of graphene to promote the “hydrogen evolution reaction,” which liberates hydrogen when an electronic current is passed through water. They developed a mathematically predicted graphene electrocatalyst and validated its performance using high-resolution electrochemical microscopy and computational modeling. The findings were reported in the Advanced Science journal.
Akichika Kumatani of Tohoku University’s Advanced Institute for Materials Research (AIMR), Tatsuhiko Ohto of Osaka University, Yoshikazu Ito of Tsukuba University, Yasufumi Takahashi of Kanazawa University, and associates in Germany and Japan discovered that addition of phosphorus and nitrogen “dopants” around the well-defined edges of graphene holes improved its potential to electrocatalyze the hydrogen evolution reaction.
Graphene-based catalysts are advantageous over metal-based counterparts because they are controllable and stable, rendering them ideal for use in energy storage and conversion devices, fuel cells, and in water electrolysis. Their properties can be enhanced by introducing multiple simultaneous modifications to their structures. However, in order to understand how they work together to support catalysis, researchers should be able to “see” these modifications at the nanoscale.
Kumatani and his teammates used the newly developed scanning electrochemical cell microscopy (SECCM) for direct, sub-microscale analysis of the electrochemical reactions that take place on passing current through water during electrolysis. In addition, it enabled them to look at how structural modifications in graphene electrocatalysts influence their electrochemical activities. Such an analysis is not possible via traditional methods.
The group produced an electrocatalyst developed from a graphene sheet alive with mathematically predicted holes with well-defined edges. The number of active sites available for chemical reactions to take place is increased by the edges around the holes. They doped the graphene sheet by introducing phosphorus and nitrogen atoms around the edges of the hole. The graphene-based electrocatalyst was subsequently employed to improve the liberation of hydrogen during electrolysis.
The research group used SECCM to find that their graphene electrocatalyst considerably enhanced the formation of current in response to energy liberation during electrolysis. Their computational estimations propose that incorporating phosphorus and nitrogen dopants improves the contrast of negative and positive charges on the atoms around hole edges, promoting their potential to carry electric current.
Phosphorus- and nitrogen-doped holey graphene electrocatalysts exhibited improved performance when compared to those doped with only one of the two chemical elements.
“These findings pave a path for atomic-level engineering of the edge structure of graphene in graphene-based electrocatalysts through the local visualization of electrochemical activities,” concluded the scientists.
Using chemical vapor deposition technique, carbon atoms were applied on a substrate. The creation of holes was made sure by silicon oxide nanoparticles on the substrate. Phosphorus and nitrogen atoms were doped. Finally, a single-layered, doped, holey graphene catalyst was produced.
JST-PRESTO “Creation of Innovative Core Technology for Manufacture and Use of Energy Carriers from Renewable Energy”; Grant-in-Aid for Scientific Research on Innovative Areas “Discrete Geometric Analysis for Materials Design”; JSPS KAKENHI; World Premier International Research Center Initiative (WPI), MEXT, Japan; NIMS microstructural characterization platform and Molecule & Material Synthesis Platform as a program of “Nanotechnology Platform Project,” MEXT, Japan; University of Tsukuba Basic Research Support Program Type S; the Iwatani Naoji Foundation; Intelligent Cosmos Academic Foundation.