Flexible Paper Based N-, P- Doped 3-D Graphene Framework Hosting Metal Oxides for Efficient Oxygen Evolution Reactions
Authors: Xin Le , Aliahmad Nojan , Xie Jian , Agarwal Mangilal 
Published: February 2020

The electrocatalytic oxygen evolution reaction (OER) is a critical anode reaction that is often coupled with an electronic/photoelectronic water splitting reaction or used in rechargeable metal-air batteries for renewable energy conversion and storage. [1] However, the sluggish OER reaction kinetics require the use of efficient electro-catalysts, such as metal oxides (e.g. IrO2, RuO2, MnO2, Co3O4, NiFeOx, etc.) or metal-free materials (e.g. N- and P- doped graphene, MWCNT, graphitic carbon nitrite, etc.). To enhance the electro-catalytic activity of OER, great efforts have been devoted to the design of hybrid materials with functionalities tuned by tailoring their micro/nano structure. In addition, pore structure and surface chemistry of supporting materials also play an important role in determining the efficiency of OER catalysis. Traditionally OER catalysts are deposited on a plenary glassy carbon electrode or indium titanium oxide (ITO) glasses, of which the low surface area greatly limits the catalyst loading. Additionally, owning to the lack of surface functionality, these substrates interact weakly with the OER catalyst, adversely affecting OER electro-catalytic activities. More importantly, the bulky and rigid electrodes make them incompatible for broad applications in energy conversion and storage systems.
Herein, we present a flexible, free standing oxygen electrode featuring 3-D architectures of high activity and durability for OERs. Conductive microfibers and paper sheets were fabricated using layer-by-layer (LbL) nano-assembly techniques, in which the cationic poly(ethyleneimine) (PEI) has been used in alternate deposition with anionic conductive PEDOT–PSS and solubilized CNT–PSS on lignocellulose wood microfibers [2]. By creating alternating layers of oppositely charged components on the surface of wood microfibers, we have produced a nanocoating of 20–150 nm thickness that enables the microfibers to exhibit electrical conductivity. Moreover, the surface charge of resultant paper can be well tuned by the LbL polyelectrolyte coating. P-, N- dual doped 3-D graphenes were then prepared with an imposing opposite charge to the composite paper. When casting functional porous graphenes onto the composite paper, it is observed that they interconnected, driven by the strong electro-static interaction. The resulting graphene coated paper, which shows high porosity and functionality, was then employed as the host framework, in which a various types of metal oxide particles of high OER activity were decorated in-situ. The obtained oxygen electrode of this hierarchy structure has exhibited improved mass and ion transport and OER efficiency was significantly enhanced. In summary, the developed smart paper consisting of orderly assembled P-, N- doped graphene layers incorporated with active OER catalyst particles performs as a flexible oxygen electrode that shows great promise in being directly applied in flexible electronic devices for efficient energy storage and conversion.

References:

[1] Y. Jiao, Y. Zheng, M. Jaroniec, S.Z. Qiao, Design of electrocatalysts for oxygen- and hydrogen-involving energy conversion reactions, Chemical Society Reviews, 44 (2015) 2060-2086.
[2] M. Agarwal, Q. Xing, B.S. Shim, N. Kotov, K. Varahramyan, Y. Lvov, Conductive paper from lignocellulose wood microfibers coated with a nanocomposite of carbon nanotubes and conductive polymers, Nanotechnology, 20 (2009).