Developing a New Water-splitting Catalyst
Journal: ACS Nano
This work actually started from 2014 when I was a 2nd year Ph.D. student in Prof. Mauricio Terrones’ group. My initial research project was to synthesize 3-dimensional carbon using graphene oxide. This research project gave me an opportunity to learn and work with graphene oxide. From that project, I learned that graphene oxide is a 2-dimensional, water soluble material with adjustable viscosity by heavily oxidizing graphene with a strong oxidant (potassium permanganate, concentrated sulfuric acid, etc.). Thus, various and abundant oxygen functional groups, such as hydroxyl groups, carbonyl groups, and carboxylic groups, are attached on the 2D sheets. I treated graphene oxide as a starting reactive material to build 3D graphene networks.
But working in a “2D group” gives me a lot of different ways to understand graphene oxide. To build a 3D carbon frame, graphene oxide can be used as the building block. To give more functionality to graphene, graphene oxide can be used as the starting material to be reactive with metal, semiconductor, and insulator. Besides, graphene oxide can also be considered as “2D surfactant sheets” to assemble other 2D layered materials on top of it. At that time, a lot of researchers were trying to find different approaches to synthesize atomically thin Van der Waals heterostructures. One of the challenges is to find a proper template/substrate to build the heterostructures. The experience working with graphene oxide gave me a hint that graphene oxide itself can solve this problem by working as both the large 2D template and surfactant to assemble other 2D materials on it. After thermal reduction, graphene oxide can be turned into conducting 2D graphene.
So, I started working on assembling WS42- and MoS42- anions onto graphene oxide. The results turned out to be exciting, since we can obtain few layer WS2 and MoS2/reduced graphene oxide heterostructures, and we can also synthesize WMoS2/reduced graphene oxide with different W to Mo ratios. However, the work was stuck, since we couldn`t find an application to utilize these unique structures. In the summer of 2016, Dr. Ruitao Lv from Tsinghua University China, visited Prof. Mauricio Terrones group as a visiting scholar. During his 3-month stay at Penn State, he advised me that these heterostructures are not useless. He mentioned that defective WS2 and MoS2 are efficient catalyst to split water into H2, and the reduced graphene oxide under-layers can work as the conducting substrates to improve the transport properties. After the discussion, he encouraged me to set up the work station for hydrogen evolution reaction measurement. After a lot of trials to get used to the data collection and interpretation, we got exciting results that the alloy/reduced graphene oxide heterostructure works more efficiently than that of pure WS2 and MoS2.
Then, the next question was to understand the superior performance of the alloy. Collaboration is the fastest way to discover and understand new science. Prof. Jose L. Mendoza-Cortes and Dr. Srimanta Pakhira from Florida State University specialize in computational science to solve engineering and pure science problems. The collaboration between two groups at PSU and FSU eventually experimentally and theoretically proved that the alloy can be used as an efficient catalyst for H2 production from water.
As a Ph.D. student at Penn State, this journey has taught me the importance of collaboration regardless of nationality. Open collaboration and communication are the keys to solving engineering and science problems. Penn State is very supportive on collaborations. As an advisor, Prof. Mauricio Terrones is always approachable no matter how busy he is, and he is always supportive to new ideas and establishing collaborations with other research groups.