(617dx) Design and Synthesis of Porous Carbon-Based Catalysts for the Electrochemical Reduction of O2 Via Either 2 e- or 4 e- Route

Authors: 
Chen, S., Stanford University
Siahrostami, S., Stanford University
To, J., Stanford University
Nordlund, D., SLAC National Accelerator Laboratory
Sinclair, R., Stanford University
Norskov, J. K., SUNCAT Center for Interface Science and Catalysis, Stanford University and SLAC National Accelerator Laboratory
Bao, Z., Stanford University
Jaramillo, T. F., Stanford University
Kim, T. R., Stanford University
Sokaras, D., SLAC National Accelerator Laboratory
Studt, F., Stanford University
To improve the cost-effectiveness, efficiency and scalability, high performance catalysts made from low cost, earth-abundant materials need to be developed. Carbon is a unique element in its ability to provide a vast range of bonding environments for heteroatoms. Carbon-based catalysts also show wide tunability, such as degree of graphitization, ultra-high surface area, adjustable pore volume and pore size distribution. [1] This leads to a tremendous flexibility for synthesizing materials with catalytic active sites of many possible structural and electronic configurations that are necessary for different electrochemical reactions. The ability to precisely control carbon structure and composition is crucial in achieving high performance carbon catalysts for any desirable application.

In this work, we explored new synthetic methods that provide high versatility in tuning carbon structure and chemical composition. In this approach, a rigid conjugated polymer network is used as the carbon precursor, which prevents pore collapsing during carbonization while allowing incorporation of various heteroatoms, such as N, B and metal ions. This facile synthetic approach allows us to synthesize the target promising structures with optimized surface motifs to catalyze reactions with targeted efficiency, stability, and selectivity, predicted by theory. In particular, the use of these porous carbon materials as electrocatalysts for oxygen reduction reaction (ORR) is explored. O2 can be either reduced to H2O via a 4 e- route with potential application in fuel cells or to H2O2, which is one of the most important industrial chemicals in the world, via a 2 e- route. [2-3] Density functional theory (DFT) modeling shows that that defective carbons with various heteroatom doping show different catalytic activity towards ORR. With the guidance of theory, we are able to use our approach to control carbon structure and composition to synthesize promising carbon catalysts. With various techniques, such as X-ray absorption spectroscopy, gas sorption, high resolution TEM, SEM and XPS, we are able to systematically characterize our carbon materials and this allows us to achieve clear understanding of the structure property relationship and design carbon materials with high electrocatalytic performance.

[1] L. Dai, Y. Xue, L. Qu, H.-J. Choi and J.-B. Baek, Chemical reviews, 2015, 115, 4823-4892.

[2] K. N. Wood, R. O'Hayre and S. Pylypenko, Energy & Environmental Science, 2014, 7, 1212-1249.

[3] J. M. Campos�Martin, G. Blanco�Brieva and J. L. Fierro, Angewandte Chemie International Edition, 2006, 45, 6962-6984.

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