Does Turnover Number Represent a Single Value or a Distribution?

Area of Science:

• Electrochemistry
• Materials Science
• Nanotechnology

Background:

• Traditional catalyst turnover number measurements are macroscopic and assume uniform catalyst longevity.
• This bulk-averaged approach masks intrinsic heterogeneity within catalyst samples.
• Meaningful comparisons across different catalytic systems are limited by this macroscopic view.

Purpose of the Study:

• To develop a novel method for simultaneously quantifying active sites and catalytic charge of individual platinum nanoparticles.
• To enable direct calculation of single-particle turnover numbers for electrochemical hydrogen evolution.
• To investigate the origins of turnover number heterogeneity at the single-particle level.

Main Methods:

• Simultaneous quantification of active sites and total catalytic charge of individual platinum nanoparticles.
• Electrochemical hydrogen evolution measurements at high current densities (>0.4 A/cm²).
• Direct calculation of single-particle turnover numbers.

Main Results:

• Revealed orders of magnitude variation in turnover numbers among monodisperse platinum nanoparticles.
• Demonstrated that heterogeneity is governed by applied potential and active-site connectivity, not primarily particle-size variation.
• Established a framework for assessing catalyst longevity distribution at the single-particle level.

Conclusions:

• Catalyst turnover number heterogeneity exists at the single-particle level.
• Applied potential and active-site connectivity are key factors influencing turnover number heterogeneity.
• This work redefines understanding of catalytic turnover number and informs strategies for enhancing catalyst durability and performance.