Hierarchically structured catalyst layer for the oxygen reduction reaction fabricated by electrodeposition of platinum on carbon nanotube coated carbon fiber

Abstract

Cost-efficient fabrication of cathode catalyst layer having low Pt-loading and high oxygen reduction reaction (ORR) performance is of prime importance towards commercialization of low temperature fuel cells. Here, an attempt has been made to fabricate hierarchically structured and cathode catalyst layer consisting of Pt-nanoparticle clusters supported on defective carbon nanotube (CNT) coated carbon fiber (CNTCF). CNTs are grown on carbon fiber (CF) by chemical vapor deposition (CVD), while electrodeposition is employed to deposit Pt-nanoparticle clusters on the CNTCF. Effect of Pt-loading on oxygen reduction reaction (ORR) performance of the Ptcoated CNTCF (Pt-CNTCF) electrocatalysts is studied by varying the electrodeposition time (ted) between 5 and 30 min, which results a variation of Pt weight fraction in Pt-CNTCF from almost zero to ~0.3. Linear sweep voltammetry using the Pt-CNTCF modified glassy carbon (GC) rotating disc electrode (RDE) is employed to study the ORR performance of the samples. The CNTCF support, owing to the defective structure of CNT, itself exhibits significant ORR activity with an electron transfer number (n) of ~2.6, which leads to a synergistic enhancement of the overall electrocatalytic performance of Pt-CNTCF. For lower Pt-loading on GC (~5 μg cm -2 ), the contribution of CNTCF support dominates, while the Pt-nanoclusters govern the ORR 2 performance at higher Pt-loading ((>10 μg cm -2 ), with n>3.5. Hence, a very low Pt-loading (~5 μg cm -2 ) may not be suitable for polymer electrolyte membrane fuel cells as production of substantial amounts of H2O2 on the catalyst supports may accelerate the membrane degradation.

Platinum Particles Electrochemically Deposited on Multiwalled Carbon Nanotubes for Oxygen Reduction Reaction in Acid Media

“…The four-electron pathway for Pt-based catalysts prepared by electrodeposition method has been reported earlier. 37,43,46 Figure 6 displays a comparison of the ORR polarization curves of Pt/MWCNT-A (Figure 6a) and Pt/MWCNT-B (Figure 6b) with commercial Pt/C measured at 1900 rpm. The values of half-wave potential (E 1/2 ) calculated from the RDE data are given in Table I.…”

“…The formation of similar clusters at certain active sites on the surface of CNTs has been reported earlier. 43,44,49 Sharma and Kar suggested that the corroded rough surface of the CNTs after acid-treatment may provide active sites for nucleation. 43 Huang et al suggested that the number of Pt nuclei formed on the carbon surface depends on the hydrophilicity and uniformity of the support material.…”

“…43,44,49 Sharma and Kar suggested that the corroded rough surface of the CNTs after acid-treatment may provide active sites for nucleation. 43 Huang et al suggested that the number of Pt nuclei formed on the carbon surface depends on the hydrophilicity and uniformity of the support material. 44 Earlier reports confirmed that formation of various functional groups in acid-treated CNTs act as nucleation sites.…”

“…Recently, many groups have contributed their efforts to figure out the optimum conditions for the electrochemical deposition of PtNPs onto the support material surface. [37][38][39][40][41][42][43][44][45][46]67,68 Porous Pt aggregates of different shape and surface morphology have been electrochemically deposited on carbon nanotube layer. 41 Basically, two different deposition techniques were applied namely, pulse electrodeposition in which the working electrode was kept switching between two constant potentials and CV at a constant scan rate.…”

“…Kar and Sharma electrochemically deposited PtNPs on CNT-coated carbon fiber (CF) for ORR. 43 Different deposition potentials and deposition time were applied to observe change in the Pt particle size. They observed the formation of discrete Pt clusters, which may be attributed to the nucleation of particles at specific active sites on the surface of CNTs.…”