Ultrahigh Electrocatalytic Activity with Trace Amount Platinum Loadings on Free-standing Mesoporous Titanium Nitride Nanotube Arrays for Hydrogen Evolution Reaction
Minimizing Pt loadings on electrocatalysts for hydrogen evolution reaction (HER) is essential for its commercial applications. Herein, free-standing mesoporous titanium nitride nanotube arrays (TiN NTAs) were fabricated to serve as the substrate for trace Pt loading. The uniform TiN NTAs show inner diameter of ~80 nm and length of ~7 μm, with many mesoporous holes in diameters ranging from 5 to 10 nm on the nanotube walls. Pt species dissolved from the Pt counter electrode in electrochemical cycling were redeposited on the mesoporous TiN NTAs to produce the Pt-TiN NTAs with an ultra-low Pt loading of 8.3 μg cm-2. The Pt-TiN NTAs exhibit 15-fold higher mass activity towards HER than the benchmark 20 wt% Pt/C in acidic media, with an overpotential of 71 mV vs. RHE at a current density of 10 mA cm-2, a Tafel slope value of 46.4 mV dec−1 and excellent stability. The performance of Pt-TiN NTAs is also much better than that of Pt species deposited on the independent nanotube arrays, due to the shortcuts originated from the mesoporous holes on the nanotube walls for electron and mass transfer.