Graphene is a unique material that has been widely investigated and found to have broad applications in fields such as energy storage, electronics, and electrocatalysis. Exploiting the advanced properties of graphene, such as high electrical conductivity, excellent chemical and mechanical stability, and large specific surface area, hybrid materials made by combining graphene with nanoparticles have led to products with much improved physical and chemical characteristics. These hybrid materials may possess superior performance when compared to either graphene or nanoparticles by themselves. This implies that there is a synergistic interaction between the graphene and nanoparticles.

The production of the graphene-nanoparticle hybrids using industrial processes such as roll-to-roll manufacturing continues to be a technical challenge. One of the challenges is the lengthy process, including graphene oxide synthesis, nanoparticle deposition, and graphene oxide reduction. Such an approach may require high reaction temperatures, a large consumption of unrecoverable solvents and acids, and/or considerable time periods, in addition to the step-wise electrode preparation.

We demonstrate here an improved method for direct preparation of metal oxide nanoparticle/graphene hybrid materials by laser induction.

—Ye et al.

Laser-induced graphene, created by James Tour and his colleagues last year, is a flexible film with a surface of porous graphene made by exposing polyimide to a commercial laser-scribing beam. Initially, the researchers made laser-induced graphene with commercially available polyimide sheets. Then, they infused liquid polyimide with boron to produce laser-induced graphene with a greatly increased capacity to store an electrical charge, which made it an effective supercapacitor.

For the latest iteration, they mixed the liquid and one of three concentrations containing cobalt, iron or molybdenum metal salts. After condensing each mixture into a film, they treated it with an infrared laser and then heated it in argon gas for half an hour at 750 ˚Celsius.

Schematic illustration of formation of MO-LIG from MC-PI film. (a) Preparation of MC-PI film from metal-complex-containing PAA solution. A MC-PAA film forms from evaporation of solvent in the metal-complex-containing PAA solution in an aluminum dish. After dehydration of PAA by heating at 200 °C under pressure, a MC-PI forms. (b) Formation of MO-LIG by laser induction on MC-PI film. The MC-PI film was subjected to a 10.6 μm CO2 laser. The area induced by the laser turns into porous structure (black region), and the area without laser-induction remains unchanged. Credit: ACS, Ye et al. Click to enlarge.

That process produced robust MO-LIGs with metallic, 10-nanometer particles spread evenly through the graphene. Tests showed their ability to catalyze the oxygen reduction reaction, an essential chemical reaction in fuel cells. Further doping of the material with sulfur allowed for hydrogen evolution, another catalytic process that converts water into hydrogen.

The wonderful thing about this process is that we can use commercial polymers, with simple inexpensive metal salts added. We then subject them to the commercial laser scriber, which generates metal nanoparticles embedded in graphene. So much of the chemistry is done by the laser, which generates graphene in the open air at room temperature.

These composites, which have less than 1 percent metal, respond as ‘super catalysts’ for fuel-cell applications. Other methods to do this take far more steps and require expensive metals and expensive carbon precursors. Remarkably, simple treatment of the graphene-molybdenum oxides with sulfur, which converted the metal oxides to metal sulfides, afforded a hydrogen evolution reaction catalyst, underscoring the broad utility of this approach.

—James Tour

Rice graduate student Ruquan Ye and Rice alumnus Zhiwei Peng, now a postdoctoral researcher at the University of Maryland, are lead authors of the paper. Co-authors are Rice graduate students Tuo Wang, Jibo Zhang and Lizanne Nilewski; Rice undergraduate Yunong Xu; and Rice alumnus Jian Lin, an assistant professor of mechanical and aerospace engineering at the University of Missouri. Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of materials science and nanoengineering and of computer science and a member of Rice’s Smalley-Curl Institute.

The Air Force Office of Scientific Research and its Multidisciplinary University Research Initiative supported the research.

Resources

• Ruquan Ye, Zhiwei Peng, Tuo Wang, Yunong Xu, Jibo Zhang, Yilun Li, Lizanne G. Nilewski, Jian Lin, and James M. Tour (2015) “In situ Formation of Metal Oxide Nanocrystals Embedded in Laser-Induced Graphene” ACS Nano doi: 10.1021/acsnano.5b04138