Palladium Nanoparticle–Graphitic Carbon Nitride Porous Synergistic Catalyst for Hydrogen Evolution/Oxidation Reactions over a Broad Range of pH and Correlation of Its Catalytic Activity with Measured Hydrogen Binding Energy

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• 作者：Tanmay Bhowmik ; Manas Kumar Kundu ; Sudip Barman
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：March 4, 2016
• 年：2016
• 卷：6
• 期：3
• 页码：1929-1941
• 全文大小：809K
• ISSN：2155-5435

文摘

The hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) in aqueous medium are two fundamental reactions for the development of non-fossil energy storage and conversion devices. In the polymer electrolyte membrane fuel cell (PEMFC) carbon supported platinum (Pt/C) based catalysts are universally used in cathodes and anodes; however, the poor durability of Pt/C due to degradation of the catalyst in the strongly oxidizing environment prevents its widespread applications. It remains a great challenge to develop new electrocatalysts with superior activity and very high durability for the HER/HOR. Here, we report the synthesis of a porous palladium nanoparticle–carbon nitride composite (Pd-CN_x) for its superior activity and high durability toward the HER/HOR in acidic and alkaline media. The Pd-CN_x composites exhibited high catalytic activity for hydrogen evolution in acidic media with a small onset potential of −12 mV and a Tafel slope of 35 mV dec^–1. At a small Pd loading of 0.043 mg cm^–2, this catalyst also exhibits a current density of 10 mA cm^–2 at a low overpotential of −55 mV with an excellent stability. The HER activity on Pd-CN_x composite is comparable to that of commercial Pt/C in acid media. The stability tests of this catalyst were done through a large number of repeated potential cycles and long-term electrolysis. These confirm the exceptional durability of this catalyst, which is much better than that of Pt/C catalysts. Furthermore, this catalyst has also displayed superior HOR activity, measured by a rotating-disk experiment with a broad range of pH (0–14) in different buffer solutions. The HER/HOR activities of porous Pd-CN_x composite in different buffer solutions were correlated with the hydrogen binding energy (HBE) of the catalyst surface. The HER/HOR activity gradually decreases with an increase in the HBE as the solution pH increases. The superior HER/HOR activities and very high durability at porous Pd-CN_x composite are due to strong bonding between Pd and carbon (Pd–C bond), the porous morphology, and synergistic interactions between Pd-NPs and the carbon nitride (CN_x) support.