Hydrogen Evolution Reaction on the Single-Shell Carbon-Encapsulated Iron Nanoparticle: A Density Functional Theory Insight

Platinum (Pt)-free catalysts for the hydrogen evolution reaction (HER) is currently a blooming research topic in view of the high cost and scarcity of Pt. Experiments on single-shell carbon-encapsulated iron nanoparticles (SCEINs) have proven comparable HER catalytic efficiency with the best Pt catalyst. However, an understanding of the structure-to-efficiency is missing. We performed ab initio density functional theory calculations on a realistic model of SCEINs, namely Fe 55 @C 240, to shed light on the catalytic properties of SCEINs and studied C 60 and C 240 fullerenes for comparison. Both the thermodynamic free energy approach (Δ G H ) and kinetic (Volmer–Heyrovský/Tafel reaction barrier E a ) calculations were realized on these systems. Our calculations proved that Fe 55 has a key role in enhancing the hydrogen binding on C 240 . Volmer–Heyrovský is the preferred mechanism, Heyrovský being the limiting reaction with E a > 1 eV. Non-zero coverage of the carbon surface enhances Δ G H without significantly affecting E a . Because the Δ G H -to- E a relationship is nonlinear, we proposed a computationally efficient strategy based on the DDEC6 bond order (BO) method to preselect potential HER sites before any calculations. E a proved to be highly site- and (C–Fe) BO-dependent, leading to the highly heterogeneous catalytic ability of Fe 55 @C 240 . Δ G H / E a best pairs can then be optimized by playing with the surface coverage.