First time investigation of Pt nanocatalysts deposited inside carbon mesopores of controlled length and diameter

This work represents the first-reported synthesis and evaluation of Pt-loaded colloid-imprinted carbon (CIC) supports consisting of a porous shell surrounding a solid core, for use as catalysts for cathodes in proton exchange membrane fuel cells (PEMFCs). Increasing the temperature of imprinting during the synthesis of CIC supports, from 250 to 400 degrees C, gave a five times increase in porous shell thickness (average pore depth), as confirmed by gas sorption and transmission electron microscopy studies. The CIC supports, all with a 26 nm pore diameter, were loaded with 20 wt% Pt and characterized with 3D transmission electron microscopy and electron tomography, showing that the Pt nanoparticles are uniformly deposited throughout the CIC pores. Using 3-electrode electrochemistry in 0.5 M H2SO4, it was found that the rate (per active Pt surface area) of the oxygen reduction reaction is independent of the pore length, with no transport limitations encountered. This demonstrates that full utilization of both the Pt and the CIC internal surface area was achieved under these experimental conditions, which promises benefits in terms of enhanced Pt utilization, thus lowering the cost and improving the durability of PEMFCs. Furthermore, this work has opened up an entirely new direction for fuel cell catalyst layer design by allowing the controlled modification of both carbon support pore diameter and pore length, also of relevance for battery and capacitor applications.