Compared to the traditional energy-intensive anthraquinone oxidation process and the direct conversion from H2 and O2 with potential hazard of explosion, the electrochemical synthesis of H2O2 from two-electron oxygen reduction reaction (2e-ORR) represents an ideal alternative solution. However, the practical application of 2e-ORR is subjected to the development of highly efficient electrocatalysts. Carbon-based materials exhibit appreciable 2e-ORR activity and selectivity in alkaline solution. However, 2e-ORR in alkaline solution is limited by the low stability of H2O2 and its weak oxidation ability. 2e-ORR in acid is much more scientifically important and practically relevant. At present, the state-of-the-art catalysts in acid are PtHg or PdHg alloys. But they are precious and sometimes high toxicity (due to the use of Hg). Among non-precious metal based candidates, molecular catalysts (porphyrins and phthalocyanines) with specific active site and tunable metal-ligand structure hold great promise, but have been relatively underexplored for 2e-ORR. This is because they readily agglomerate via intermolecular π-π stacking to form particles with few accessible surface sites. The possible solution is to construct porous frameworks to increase the surface exposure of active sites. Hydrogen-bonded organic frameworks (HOFs) are a large family of porous two-dimensional (2D) or three-dimensional (3D) frameworks materials with high crystallinity, great surface areas, and abundant porosity.
Recently, Professor Yanguang Li and Lu Wang of our institute, together with other researchers developed highly efficient HOFs for 2e-ORR. In their work, they first carried out high-throughput DFT computational screening for metalloporphyrins with various metal centers, and identified cobalt porphyrin to have the best 2e-ORR activity and selectivity. As guided by the theoretical predictions, they accordingly prepared hydrogen-bonded cobaltoporphyrin frameworks (PFC-72-Co) with high structural crystallinity, large surface areas, and abundant catalytic sites from the self-assemble of 5,10,15,20-(tetra-4-carboxyphenyl) porphyrin (TCPP-Co) in solutions. PFC-72-Co enabled efficient and stable H2O2 production in acid with an onset potential of ~0.68 V (20 mV overpotential), >90% H2O2 selectivity at 0-0.6 V and high TOF value of 10.9 s-1 at 0.55 V, far superior to most of electrocatalysts in acid. This study represented the first demonstration of hydrogen-bonded metalloporphyrin frameworks for electrocatalysis that might expand the potential applications of these interesting materials.
Title: Theory-guided design of hydrogen-bonded cobaltoporphyrin frameworks for highly selective electrochemical H2O2 production in acid
Authors: Xuan Zhao#, Qi Yin#, Xinnan Mao#, Chen Cheng, Liang Zhang, Lu Wang*, Tian-Fu Liu*, Youyong Li & Yanguang Li*
Link to Paper: https://www.nature.com/articles/s41467-022-30523-0
Link to Prof. Li’s group: http://www.ligroup.com.cn/
Acknowledgement: The authors acknowledge the support from the Ministry of Science and Technology of China (2017YFA0204800 and 2018YFA0208600), the National Natural Science Foundation of China (U2002213, 52161160331, 22071246, and 22005305), the Science and Technology Development Fund Macau SAR (0077/2021/A2), the Collaborative Innovation Center of Suzhou Nano Science and Technology, the 111 Project and Joint International Research Laboratory of Carbon-Based Functional Materials and Devices. The authors thank SSRF (beamline 11B) and BSRF (beamline 1W1B) for the allocation of synchrotron beamtime.
Editor: Guo Jia