Rice University lab develops dual-surface graphene electrode to split water into hydrogen and oxygen
Researchers in the Rice University lab of chemist James Tour have produced dual-surface laser-induced graphene (LIG) electrodes on opposing faces of a plastic sheet that split water into hydrogen on one side and oxygen on the other side. The high porosity and electrical conductivity of LIG facilitates the efficient contact and charge transfer with the requisite electrolyte. A paper on the work is published in the journal ACS Applied Materials and Interfaces.
The LIG-based electrodes exhibit high performance for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with excellent long-term stability. The overpotential reaches 100 mA/cm2 for HER and OER is as low as 214 and 380 mV with relatively low Tafel slopes of 54 and 49 mV/dec, respectively. (One decade (symbol dec) is a factor of 10 difference between two numbers measured on a log scale.)
By serial connecting of the electrodes with a power source in an O-ring setup, H2 and O2 are simultaneously generated on either side of the plastic sheet at a current density of 10 mA/cm2 at 1.66 V and can thereby be selectively captured.
The team said that said their demonstration provides a promising route to simple, efficient and complete water splitting, and that the inexpensive material may be a practical component in generating the hydrogen for use in future fuel cells.
… the sluggish kinetics of hydrogen and oxygen evolution reactions (HER and OER, respectively) in water splitting requires catalysts to increase the efficiencies. Apart from the noble metal materials such as Pt, RuO2 and IrO2, numerous noble-metal-free catalysts have been developed. For example, transition-metal carbides, phosphides and sulfides have shown favorable performance in HER. The oxides/hydroxides of cobalt, nickel, manganese and iron also have proven to be efficient catalysts for OER. However, for the scalable production of H2 and O2, the catalytic electrodes should be easily fabricated to minimize their overall cost. It is therefore desirable to couple the HER and OER processes into a single simple package.
Laser-induced graphene (LIG) is a 3D porous graphene material fused to a flexible substrate that is prepared by a one-step laser scribing process on commercial polyimide … While LIG has been used for direct patterning applications in microsupercapacitors and related devices, in this study we exploit the LIG process to fabricate efficient catalytic electrodes for splitting water to H2 and O2 starting from a single sheet of plastic.—Zhang et al.
LIG is produced by treating the surface of a sheet of polyimide, an inexpensive plastic, with a laser. Rather than a flat sheet of hexagonal carbon atoms, LIG is a foam of graphene sheets with one edge attached to the underlying surface and chemically active edges exposed to the air.
LIG itself is inert, so turning it into a water splitter involves a few more steps. First, the lab impregnated the side of the plastic destined to pull hydrogen from water with platinum particles; then the lab used a laser to heat the surface and make LIG. The Rice material uses only a quarter of the platinum found in commercial catalysts, said Jibo Zhang, a Rice graduate student and lead author of the paper.
The other side, for oxygen evolution, was first turned into LIG and then enhanced with nickel and iron through electrochemical deposition. Both sides showed low onset potentials (the voltage needed to start a reaction) and strong performance over 1,000 cycles.
The lab came up with another variation: making the polyimide into an LIG catalyst with cobalt and phosphorus that could replace either the platinum or nickel-iron sides to produce hydrogen or oxygen. While the low-cost material benefits by eliminating expensive noble metals, it sacrifices some efficiency in hydrogen generation, Tour said.
When configured with cobalt-phosphorus for hydrogen evolution and nickel-iron for oxygen, the catalyst delivered a current density of 10 milliamps per square centimeter at 1.66 volts. It could be increased to 400 milliamps per square centimeter at 1.9 volts without degrading the material. The current density governs the rate of the chemical reaction.
Tour said enhanced LIG offers water-splitting performance that’s comparable and often better than many current systems, with an advantage in its inherent separator between oxygen and hydrogen products. He noted it may find great value as a way to chemically store energy from remote solar or wind power plants that would otherwise be lost in transmission.
The material might also serve as the basis for efficient electrocatalysis platforms for carbon dioxide or oxygen reduction, he said.
Co-authors are graduate students Chenhao Zhang, Huilong Fei, Yilun Li and Junwei Sha. Sha is also a student at Tianjin University and the Collaborative Innovation Center of Chemical Science and Engineering, Tianjin, China. Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of computer science and of materials science and nanoengineering at Rice.
The research was supported by the Air Force Office of Scientific Research, the National Science Foundation-funded and Rice-based Nanotechnology-Enabled Water Treatment Engineering Research Center and the Chinese Scholarship Council.
Jibo Zhang, Chenhao Zhang, Junwei Sha, Huilong Fei, Yilun Li, and James M. Tour (2017) “Efficient Water Splitting Electrodes Based on Laser-Induced Graphene” ACS Applied Materials & Interfaces doi: 10.1021/acsami.7b06727