ic8b00543_si_001.pdf (3.68 MB)
Energy-Efficient Hydrogen Evolution by Fe–S Electrocatalysts: Mechanistic Investigations
journal contribution
posted on 2018-06-12, 13:34 authored by Kai-Ti Chu, Yu-Chiao Liu, Min-Wen Chung, Agus Riyanto Poerwoprajitno, Gene-Hsiang Lee, Ming-Hsi ChiangThe intrinsic catalytic
property of a Fe–S complex toward H2 evolution was
investigated in a wide range of acids. The title complex exhibited
catalytic events at −1.16 and −1.57 V (vs Fc+/Fc) in the presence of trifluoromethanesulfonic acid (HOTf) and
trifluoroacetic acid (TFA), respectively. The processes corresponded
to the single reduction of the Fe-hydride-S-proton and Fe-hydride
species, respectively. When anilinium acid was used, the catalysis
occurred at −1.16 V, identical with the working potential of
the HOTf catalysis, although the employment of anilinium acid was
only capable of achieving the Fe-hydride state on the basis of the
spectral and calculated results. The thermodynamics and kinetics of
individual steps of the catalysis were analyzed by density functional
theory (DFT) calculations and electroanalytical simulations. The stepwise
CCE or CE (C, chemical; E, electrochemical) mechanism was operative
from the HOTf or TFA source, respectively. In contrast, the involvement
of anilinium acid most likely initiated a proton-coupled electron
transfer (PCET) pathway that avoided the disfavored intermediate after
the initial protonation. Via the PCET pathway, the heterogeneous electron
transfer rate was increased and the overpotential was decreased by
0.4 V in comparison with the stepwise pathways. The results showed
that the PCET-involved catalysis exhibited substantial kinetic and
thermodynamic advantages in comparison to the stepwise pathway; thus,
an efficient catalytic system for proton reduction was established.