Gas diffusion layers (GDLs) in the proton exchange membrane fuel cells (PEMFCs) enable the distribution of reactant gases to the reaction zone in the catalyst layers by controlling the water in the pore channels apart from providing electrical and mechanical support to the membrane electrode assembly (MEA). In the present work, we report the in situ growth of carbon nanotubes nanoforest (CNN) directly onto macro‐porous carbon paper substrates. The surface property as analysed by a Goniometer showed that the CNN/carbon paper surface is highly hydrophobic. CNN/carbon paper was employed as a GDL in an MEA using Nafion‐212 membrane as an electrolyte and evaluated in single cell PEMFCs. While the GDLs prepared by wire‐rod coating process have major performance losses at lower humidities, the in situ CNN/carbon paper, developed in this work, shows very stable performance at all humidity conditions demonstrating a significant improvement for fuel cell performance. The CNN/carbon‐based MEAs showed very stable performance with power density values of ∼1,100 and 550 mW cm–2, respectively, both using O2 and air as oxidants at ambient pressure.

An experimental method is introduced to measure platinum oxide coverage in situ on proton exchange membrane fuel cell electrodes using pulse voltammetry. The in situ nature of this technique allows us to investigate temperature and relative humidity effects at 120 C and 80 C with 50% and 25% relative humidity with the use of real fuel cell electrodes. Higher relative humidity conditions appeared to increase the platinum oxide coverage as evidenced by the oxide stripping current in the chronoamperometric response. This observation confirms that water is involved in the platinum oxide formation mechanism. For oxide conditioning times longer than 1 second, a linear logarithmic rate for oxide formation on platinum is observed. These findings suggest that higher water content in the PEMFC cathode at open circuit or low current density demand will lead to higher rates of electrode degradation.

Normal pulse voltammetry (NPV) is applied to operating proton exchange membrane fuel cells (PEMFCs) using a high current potentiostat. Kinetic information including the Tafel slope and exchange current density for the oxygen reduction reaction (ORR) is directly extracted from the steady state voltammetric response obtained from the NPV experiment.Temperature, relative humidity, and conditioning potential are varied independently to observe their effect on the PEMFC through the Tafel slope calculation. This NPV technique provides kinetic information previously collected through ex situ techniques such as rotating disc electrodes. The ability to probe in situ the kinetic effects of catalysts within operational PEMFCs has never been proposed in this detail. NPV measurements take less than 30 seconds to conduct thus making the process simple and efficient. The observed Tafel slope is about 60mV/decade for oxide covered platinum and 120mV/decade for oxide free platinum.