Covalently functionalized layered MoS<sub>2</sub> supported Pd nanoparticles as highly active oxygen reduction electrocatalysts
Dimitrios K. Perivoliotis, Yuta Sato, Kazu Suenaga, Nikos Tagmatarchis
Abstract
Molybdenum disulfide nanosheets covalently modified with a 1,2-dithiolane derivative were used as a novel substrate for the immobilization of Pd nanoparticles (PdNPs) towards the development of a highly efficient hybrid electrocatalyst, namely PdNPs/f-MoS2, for the oxygen reduction in an alkaline medium. The newly prepared hybrid material was thoroughly characterized through complementary techniques such as Raman and IR spectroscopy, TGA, HRTEM, STEM/EELS, and EDS. The PdNPs/f-MoS2 nanohybrid exhibited excellent performance towards oxygen electroreduction with a positive onset potential of +0.066 V and a half-wave potential of -0.116 V vs. Hg/HgO, along with a high current response, which are superior to those of its graphene counterpart and comparable to those of the benchmark Pd/C product. Moreover, PdNPs/f-MoS2 was proved to be remarkably stable as chronoamperometric assays showed minimum activity loss among the tested materials, clearly outperforming the commercial catalyst. The excellent performance of PdNPs/f-MoS2 is attributable to (i) the high affinity of the catalytic PdNPs with the f-MoS2 substrate, (ii) the absence of any capping agent for the stabilization of PdNPs onto f-MoS2, and more importantly (iii) the preservation of the integrity of the MoS2 basal plane during the functionalization process. Lastly, the oxygen reduction on PdNPs/f-MoS2 proceeded through the energy efficient four-electron pathway, showing great potential for the use of layered transition metal dichalcogenides in energy conversion applications, comprising fuel cells.