Figure 2. a) Contact angle measurements of CP and ACP. b) Contact angle
measurements of CP/Ru and ACP/Ru. Snapshots of AIMD simulations for
anchoring process of RuCl3 on c) pristine CP and d) ACP.
Color codes: cyan (Ru), light green (Cl), red (O), white (H), and grey
(C).
The crystal structures were analyzed by X-ray diffraction (XRD)
(Figure 3 a). The XRD pattern exhibits two prominent peaks at
approximately 26 and 54° which corresponds to the (002) and (211) planes
of graphitic carbon, respectively. Due to the predominance of graphitic
carbon peaks, the specific region of interest was magnified as presented
in Figure 3b. Within this magnified region, both samples displayed a
distinct peak at approximately 43°, indicating the presence of Ru (002)
plane. Hydrogen temperature-programmed desorption
(H2-TPD) was performed to investigate the kinetics of
hydrogen adsorption and desorption on the electrode to understand the
interaction between Ru atoms and hydrogen.[27] The
lack of any peaks in the H2-TPD profile across the
temperature range of 25 to 550 ℃ for the bare CP indicates its
inherently inferior electrochemical characteristics, which will be
further discussed in the following sections. Meanwhile,
ACP/RuSAC+C shows H2 desorption starting
at 300 ℃, with a prominent peak observed at around 500 ℃. This result
aligns with previous research, where Ru-based catalysts typically
exhibited desorption peaks within the temperature range of approximately
300 to 500 ℃ (Figure 3c).[28-31] To gain further
insight into the existing form of Ru atoms in
ACP/RuSAC+C, transmission electron microscopy (TEM) and
aberration-corrected (AC) high-angle annular dark-field scanning
transmission electron microscopy (HAADF-STEM) measurements were
conducted. Notably, these analyses revealed the presence of both Ru
nanoclusters and a significant number of atomically distributed Ru atoms
surrounding the nanoclusters (Figure 3d,e). Hence, we confirmed that the
Ru atoms in ACP/RuSAC+C exist as both single atoms and
nanoclusters. The lattice spacing of the Ru nanoclusters in
ACP/RuSAC+C is ~0.216 nm, corresponding
to the (002) plane of the Ru nanoclusters, which is in agreement with
the XRD results. Moreover, statistical analysis, as presented in Figure
3f,g, demonstrates that the average distance between Ru single atoms and
the closest nanoclusters is typically 4.24 ± 0.13 Å. Energy-dispersive
X-ray spectroscopy (EDS) analysis revealed uniform distributions of Ru,
N, O, and C elements in the carbon matrix (Figure 3h).