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Hong Wang2 Tom Wu2 Weiyi Zhang1 Yongneng Wu1 Jiayin Yuan1

2, King Abdullah University of Science and Technology (KAUST), Thuwal, , Saudi Arabia
1, Clarkson University, Potsdam, New York, United States

Carbon materials have been widely used as one of the candidates to address global energy and environmental issues due to their extraordinary, tuneable physicochemical properties, rich abundance and low cost. Freestanding porous carbon membranes particularly hold great promise in the fields of catalysis, water treatment, biofiltration, gas separation and optoelectronics, just to name a few, due to their structural integrity, continuity and purity. Typical synthetic methods involve mechanical rolling of thermally expanded graphite flakes, chemical vapour deposition and vacuum filtration of dispersions of graphene sheets or carbon nanotubes. In addition pyrolysis of thermosetting polymer precursors could lead to carbon membrane sieves with micropores, which exhibited high-performance for gas separation. Precise control over the atomic order, local chemical composition, nanoscale morphology and complex pore architecture, as well as easy access to porous membranes of large size and large surface area, is highly relevant but can hardly be fully met by the state-of-the-art synthetic protocols. Particularly, a high degree of graphitization and hierarchical pore architecture with interconnected pores over a broad length scale are eagerly being pursued because they could offer fast electron conduction, and rapid mass transport through large pores along with a simultaneously high-reaction capacity via the large accessible surface area provided by the micro/mesopores.

Through a bottom–up approach, we are able to fabricate hierarchically structured, nitrogen-doped, graphitic nanoporous carbon membranes from their porous polymer counterpart. In particular, the pores along the membrane cross-section assume a gradient distribution in their sizes, which is seldom observed in such membranes. The pristine nanoporous carbon membranes exhibit unusual single-crystal-like characteristics across their entire body. As a prototypical application, when loaded with cobalt nanoparticles, these highly conductive porous carbon membranes due to the binder-free nature serve as an active carbon-based bifunctional electrocatalyst for overall water splitting. In addition, by loading Co/CoP Janus-type nanocrystals, such hybrid membranes serves as excellent hydrogen evolution electrode in both acid and alkaline environment.

References
[1] Wang, H.; Yuan, J.; Wu, T., et al., Nat. Commun. 2017, 8, 13592.
[2] Wang, H.; Yuan, J.; Wu, T., et al., ACS Nano, 2017, 11 (4), 4358–4364.

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