Determination of optimum Pd:Ni ratio for PdxNi100-x/CNTs formic acid electrooxidation catalysts synthesized via sodium borohydride reduction method

The main purpose of this study is to investigate the optimum Pd:Ni molar ratio for carbon nanotube-supported PdNi (PdxNi100-x/CNT) alloy catalysts toward formic acid electrooxidation (FAE). NaBH4 reduction method was employed for the synthesis of Pd90Ni10/CNT, Pd70Ni30/CNT, Pd50Ni50/CNT, and Pd40Ni60/CNT. Synthesized catalysts were characterized by employing advanced surface analytical techniques, namely, X-ray diffraction (XRD), transmission electron microscopy (TEM), N-2 adsorption-desorption, and inductively coupled plasma-mass spectrometry (ICP-MS). The characterization results showed that all catalysts were successfully synthesized at desired molar composition. Pd90Ni10/CNT displayed the highest specific and mass activities with 2.32 mA/cm(2) and 613.9 mA/mg Pd, respectively. Specific activity of the Pd90Ni10/CNT was found approximately 3.6, 2.3, 11.1, and 3.4 times higher than those of Pd70Ni30/CNT, Pd50Ni50/CNT, Pd40Ni60/CNT, and Pd/CNT, respectively. The synergistic effect between Pd and Ni at optimized metal ratio was utilized to obtain an improvement in specific activity. Furthermore, Pd90Ni10/CNT showed the lowest charge transfer resistance (R-ct) and a long-term stability. To our knowledge, this is the first study reporting the optimization of atomic molar composition for PdxNi100-x/CNT catalysts toward FAE.