UC San Diego

Graphene oxide is a promising nanomaterial due to its surface versatility by substitution of functional groups and controllable d-spacing. However, most common methods to prepare graphene oxide are based on chemical exfoliation by strong oxidation agents forming small flake dispersions that are used to form thin films of aggregatedflakes. These methods are problematic due to the high amount of crack formation during the oxidation process. Due to their discontinuous and amorphous morphology, graphene oxide films have poor thermal, electronic and mechanical properties. To improve their poor performance, increasing the mean area (>10 µm) of the flakes is the best strategy. Common large area graphene oxide synthesis methods focus on chemical or mechanical exfoliation techniques for production. These techniques are outdated and still need to be assembled into a film for device fabrication. However, we developed and studied a novel and quick method to obtain large and continuous graphene oxide multilayers by directly converting a chemical vapor deposited multilayer graphene into graphene oxide. Our direct conversion of graphene to graphene oxide shows great promise for further improved transport properties and enhanced performance for filtering, molecule separation, binderless batteries, and metal detection. The size of the novel graphene oxide has been grown up to 225 mm2, which is 4 orders of magnitude larger than flake processes can produce. When reduced, the film shows a conductivity increase of 40% compared to other large sheet graphene oxide. To test this novel large area graphene oxide for applications we developed a sensor low level detection of Pb2+ in water and an ultrathin, binderless, silicon intercalated anode for lithium ion batteries. The sensor has a limit of detection of 0.21 nM and 0.101 nM for electrochemical and electric analysis, respectively. This is lower than the recommended limit provided by the Wolrd Health Organization and two magnitudes lower than epitaxial graphene can achieve. The binderless silicon intercalated anode shows a specific capacity of 2247 mAh/g, an efficiency of 98% over 90 cycles, a diameter of 15 mm, and a thickness of 5 µm. This is 60% thinner than the thinnest reported binderless anode and has the unique ability to grow silicon nanowires on its surface via oxide assisted growth mechanism.