posted on 2024-03-08, 20:06authored byDipankar Saha, Hsin-Jung Yu, Jiacheng Wang, Prateek, Xiaobo Chen, Chaoyun Tang, Claire Senger, James Nicolas Pagaduan, Reika Katsumata, Kenneth R. Carter, Guangwen Zhou, Peng Bai, Nianqiang Wu, James J. Watkins
Current electrocatalysts for oxygen evolution reaction
(OER) are
either expensive (such as IrO2, RuO2) or/and
exhibit high overpotential as well as sluggish kinetics. This article
reports mesoporous earth-abundant iron (Fe)–nitrogen (N) doped
carbon electrocatalysts with iron clusters and closely surrounding
Fe–N4 active sites. Unique to this work is that
the mechanically stable mesoporous carbon-matrix structure (79 nm
in pore size) with well-dispersed nitrogen-coordinated Fe single atom-cluster
is synthesized via rapid thermal annealing (RTA) within only minutes
using a self-assembled bottlebrush block copolymer (BBCP) melamine–formaldehyde
resin composite template. The resulting porous structure and domain
size can be tuned with the degree of polymerization of the BBCP backbone,
which increases the electrochemically active surface area and improves
electron transfer and mass transport for an effective OER process.
The optimized electrocatalyst shows a required potential of 1.48 V
(versus RHE) to obtain the current density of 10 mA/cm2 in 1 M KOH aqueous electrolyte and a small Tafel slope of 55 mV/decade
at a given overpotential of 250 mV, which is significantly lower than
recently reported earth-abundant electrocatalysts. Importantly, the
Fe single-atom nitrogen coordination environment facilitates the surface
reconstruction into a highly active oxyhydroxide under OER conditions,
as revealed by X-ray photoelectron spectroscopy and in situ Raman spectroscopy, while the atomic clusters boost the single atoms
reactive sites to prevent demetalation during the OER process. Density
functional theory (DFT) calculations support that the iron nitrogen
environment and reconstructed oxyhydroxides are electrocatalytically
active sites as the kinetics barrier is largely reduced. This work
has opened a new avenue for simple, rapid synthesis of inexpensive,
earth-abundant, tailorable, mechanically stable, mesoporous carbon-coordinated
single-atom electrocatalysts that can be used for renewable energy
production.