Improving Pd-N-C fuel cell electrocatalysts through fluorination-driven rearrangements of local coordination environment

The local coordination environment around catalytically active sites plays a vital role in tuning the activity of electrocatalysts made of carbon-supported metal nanoparticles. However, the rational design of electrocatalysts with improved performance by controlling this environment is hampered by synthetic limitations and insufficient mechanistic understanding of how the catalytic phase forms. Here we show that introducing F atoms into Pd/N-C catalysts modifies the environment around the Pd and improves both activity and durability for the ethanol oxidation reaction and the oxygen reduction reaction. Our data suggest that F atom introduction creates a more N-rich Pd surface, which is favourable for catalysis. Durability is enhanced by inhibition of Pd migration and decreased carbon corrosion. A direct ethanol fuel cell that uses the Pd/N-C catalyst with F atoms introduced for both the ethanol oxidation reaction and oxygen reduction reaction achieves a maximum power density of 0.57 W cm(-2) and more than 5,900 hours of operation. Pd/C catalysts containing other heteroatoms (P, S, B) can also be improved through the addition of F atoms. Metal- and N-coordinated carbon materials are promising electrocatalysts, but improved activity and stability are desirable for fuel cell applications. Chang et al. address this by introducing F atoms into Pd/N-C catalysts, modifying the environment around the Pd and enhancing performance for ethanol oxidation and oxygen reduction.