Preparation of Cu-Pd bimetallic nanoporous carbon composite and its application as electrocatalyst for hydrogen evolution reaction

Nowadays, fuel cell become promising power sources due to owing to its low pollutant emission, renewable energy, and high-energy conversion efficiency [1]. Hydrogen, H2, is being consideredas an energy carrier and one of the most important fuel in the fuel cell technology. Therefore, there are many attempts to use different electrodes (with the minimum of Pt content) for the hydrogen evolution reaction (HER). For this purpose, variety of porous materials are used as electrocatalyst towards HER. The metal-organic framework-derived nanoporous carbon (MDNPC) due to high surface area, good conductivity and easy synthesis method are applied asa support for preparation of electrocatalyst. The MDNPC is synthesized by indirect and direct carbonization of different metal organic frameworks (MOFs). In this article, MOF-199 are used as template to synthesis of Cu/nanoporous carbon composite (Cu/NPCC) by direct carbonization under N2 atmosphere at 900 °C. There are different methods to preparation of MOFs, such as:hydrothermal, microwave-assisted, mechanochemical, sonochemical and recently, electrochemical techniques [2-4]. Among these methods, electrochemical techniques haveseveral advantages, such as: mild synthesis conditions, shorter synthesis times, and thepossibility to control the reaction conditions directly during the synthesis process and higher conductivity by the addition of an electrolyte and thus, a lower ohmic drop, results in a higheryield and production rate of MOFs. In this method, an electrode is used as the source of metal ions. The electrode is placed in a solution of the linker, often also containing an electrolyte. Upon applying an appropriate voltage or current, the metal dissolves and the metal ions requiredfor the MOF formation are released near the electrode surface. Also, Anodic dissolution eliminates the use of metal salts, preventing their entrapment in the MOF pores. However, the use of conducting salts can result in entrapment and care must be taken to remove them. In this article, the MOF-199 are synthesized by hydrothermal and electrochemical synthesis methods and the effect of synthesis producers are investigated on its catalytic performance for HERelectrocatalysis. The Cu-Pd/nanoporous carbon composite-electrochemical (Cu-Pd/NPCCelectro)and Pd/nanoporous carbon composite-hydrothermal (Cu-Pd/NPCC-hydro) were synthesized by utilization of Cu/NPCC-electro and Cu/NPCC-hydro as a precursor for galvanicreplacement reaction (GRR) of its Cu atoms by Pd (IV) ions, upon immersion in a palladium chloride solution. The synthesized materials was characterized by XRD, SEM, FT-IR, and BET technique. Electrochemical characterization was performed in a conventional three-electrodecell. An AgǀAgClǀKCl (3M) and a platinum wire served as reference and counter electrodes, respectively. To prepare of working electrode, 7 μL of suspended Cu-Pd/NPCC-electro and Cu- Pd/NPCC-hydro in ethanol (without adding any binder and conductive agents) were deposited onto glassy carbon electrode. The electrocatalytic activity of the as-fabricated electrodes for HER was investigated by LSV technique over the potential range from 0 to -1.0 V vs. AgǀAgClǀKCl (3M), and results were shown in Figure 1. The results showed that the Cu- Pd/NPCC-electro has a more positive effect on the reduction of hydrogen ions in H2SO4 solution. This behavior can be related to high conductivity of Cu-Pd/NPCC-electro due to high electron transfer site in electrochemical synthesized MOF-199 and lower charge transfer resistance that demonstrated in electrochemical impedance spectroscopy (EIS) studies.

کلیدواژه ها:

MOF- 199 ، Electrosynthesis ، MOF-derived nanoporous carbon ، Cu-Pd bimetallic nanocomposite ، Galvanic replacement ، Hydrogen evolution reaction