Key Factors for Simultaneous Improvements of Performance and Durability of Core‐Shell Pt₃Ni/Carbon Electrocatalysts Toward Superior Polymer Electrolyte Fuel Cell

Abstract

It remains a big challenge to remarkably improve both oxygen reduction reaction (ORR) activity and long‐term durability of Pt−M bimetal electrocatalysts simultaneously in the harsh cathode environment toward widespread commercialization of polymer electrolyte fuel cells (PEFC). In this account we found double‐promotional effects of carbon micro coil (CMC) support on ORR performance and durability of octahedral Pt3Ni nanoparticles (Oh Pt3Ni/CMC). The Oh Pt3Ni/CMC displayed remarkable improvements of mass activity (MA; 13.6 and 34.1 times) and surface specific activity (SA; 31.3 and 37.0 times) compared to those of benchmark Pt/C (TEC10E20E) and Pt/C (TEC10E50E‐HT), respectively. Notably, the Oh Pt3Ni/CMC revealed a negligible MA loss after 50,000 triangular‐wave 1.0–1.5 VRHE (startup/shutdown) load cycles, contrasted to MA losses of 40 % (TEC10E20E) and 21.5 % (TEC10E50E‐HT) by only 10,000 load cycles. It was also found that the SA increased exponentially with the decrease in the CO stripping peak potential in a series of Pt−M/carbon (M: Ni and Co), which predicts a maximum SA at the curve asymptote. Key factors for simultaneous improvements of performance and durability of core‐shell Pt3Ni/carbon electrocatalysts toward superior PEFC is also discussed.

Plasma-Devised Pt/C Model Electrodes for Understanding the Doubly Beneficial Roles of a Nanoneedle-Carbon Morphology and Strong Pt-Carbon Interface in the Oxygen Reduction Reaction

“…At 0.4 V, a potential in the double layer, the APD-Pt/nanoneedles-GC showed a higher Pt 5d vacancy than a benchmark Pt/C. Interestingly, a suppressed increment in the white line intensity was observed with raising potentials from 0.4 to 1.0 V RHE , similar to the case of Pt alloys. − The results demonstrate that the Pt 5d vacancy was tuned by the strong contact between APD-Pt and nanoneedles-GC. The subsequently decreasing potential (cathodic scan) works for the desorption of oxygenated species and recovery of the metallic Pt state.…”

“…Little hysteresis (even negligible hysteresis within the experimental error bars) was observed in the loop of the potential cycling (Figure c), which indicates a lesser amount of strongly adsorbed surface oxides at 1.0 V RHE for the APD-Pt/nanoneedles-GC. The size of the hysteresis loops approximately scales with the durability (MA loss). ,, The suppression of the strong adsorption of oxygenated species in the anodic direction and the relieved cathodic dissolution due to few hysteresis loops contribute to the robust durability for the APD-Pt/nanoneedles-GC. The oxygen species adsorbed on the APD-Pt/nanoneedles-GC surface at 1.0 V RHE are readily reduced below 1.0 V RHE , also resulting in the higher ORR performance. ,− Fourier transformed EXAFS data for the APD-Pt/nanoneedles-GC at both 0.4 and 1.0 V RHE showed no Pt–O bonds except Pt–Pt bonds (Figure d and Table S1).…”

“…The size of the hysteresis loops approximately scales with the durability (MA loss). ,, The suppression of the strong adsorption of oxygenated species in the anodic direction and the relieved cathodic dissolution due to few hysteresis loops contribute to the robust durability for the APD-Pt/nanoneedles-GC. The oxygen species adsorbed on the APD-Pt/nanoneedles-GC surface at 1.0 V RHE are readily reduced below 1.0 V RHE , also resulting in the higher ORR performance. ,− Fourier transformed EXAFS data for the APD-Pt/nanoneedles-GC at both 0.4 and 1.0 V RHE showed no Pt–O bonds except Pt–Pt bonds (Figure d and Table S1). The results on the active and durable APD-Pt/nanoneedles-GC are entirely different from those for the Pt/C, which showed a increase in the white line intensity above 0.8 V RHE and the existence of Pt–O bonds in addition to Pt–Pt bonds at 1.0 V RHE . ,− It is, in general, hard to detect Pt–C interface bonding due to a mismatch of the lattice parameters and disordered carbon surfaces diminishing Pt–C contribution .…”

“…The oxygen species adsorbed on the APD-Pt/nanoneedles-GC surface at 1.0 V RHE are readily reduced below 1.0 V RHE , also resulting in the higher ORR performance. ,− Fourier transformed EXAFS data for the APD-Pt/nanoneedles-GC at both 0.4 and 1.0 V RHE showed no Pt–O bonds except Pt–Pt bonds (Figure d and Table S1). The results on the active and durable APD-Pt/nanoneedles-GC are entirely different from those for the Pt/C, which showed a increase in the white line intensity above 0.8 V RHE and the existence of Pt–O bonds in addition to Pt–Pt bonds at 1.0 V RHE . ,− It is, in general, hard to detect Pt–C interface bonding due to a mismatch of the lattice parameters and disordered carbon surfaces diminishing Pt–C contribution . We further measured contact angles (Figure e,f) and the surfaces of nanoneedles-GC and flat-GC were found to be hydrophobic and hydrophilic, respectively, which confirms that the nanoneedle structure modified the hydrophobicity/hydrophilicity of the GC surface.…”

“…The size of the hysteresis loops approximately scales with the durability (MA loss). 18,44,45 The suppression of the strong adsorption of oxygenated species in the anodic direction and the relieved cathodic dissolution due to few hysteresis loops contribute to the robust durability for the APD-Pt/nanoneedles-GC. The oxygen species adsorbed on the APD-Pt/nanoneedles-GC surface at 1.0 V RHE are readily reduced below 1.0 V RHE , also resulting in the higher ORR performance.…”