2 Atomically Precise Nanoclusters as Electrocatalysts
43
2.3 Hydrogen Evolution Reaction with Metal NC Catalysts
The hydrogen evolution reaction (HER) occurs at the cathode when an external
voltage is applied. The reaction can be described in three steps:
Volmer reaction:
H
+
+ M + e
−
→ MH ads (acidic)
(2.1)
H 2 O + M + e
−
→ MH ads + OH
−
(alkaline)
(2.2)
In the Volmer reaction, hydrogen absorbs on the catalytic material to form a MH ads
intermediate, followed by a Heyrovsky reaction or Tafel reaction. In the Heyrovsky
reaction, the dihydrogen is formed through an electrochemical desorption:
MH ads + H
+
+ e
−
→ M + H 2 (acidic)
(2.3)
MH ads + H 2 O + e
−
→ M + OH
−
+ H 2 (alkaline)
(2.4)
The hydrogen can also undergo a chemical desorption process through the Tafel
reaction:
2 MH ads → 2 M + H 2
(2.5)
The binding energy of hydrogen to the catalyst is the key factor of HER activity.
Among the HER catalysts, noble metals such as Pt and Pd have moderate binding
energy with hydrogen, thus showing excellent HER activities [25]. However, the
high cost and stability issue of Pt catalysts motivate the scientists to find alternative
materials for HER.
Here, we summarize the doping effects and synergetic effects of Au NCs in HER.
We also introduce how the computational technique is used in these cases to explain
differences in catalytic activity and verify proposed mechanisms. These works offer
some insights into the catalytic reactions, which is expected to further pave the way
for future design of catalyst materials.
2.3.1 Pt or Pd Doped Au 25 NCs in HER
The study of Au NCs as HER catalysts was reported by Kyuju et al. in 2017 [26].
A molecular-like Pt 1 Au 24 nanocluster was prepared and used as catalysts in homogeneous HER. Following this work, the same group further studied the Pd 1 Au 24 ,
Pd 2 Au 36 and Pt 2 Au 36 nanoclusters [27]. In the case of Au 25 nanocluster, the doping
atom (Pd or Pt) exclusively replaces the central gold atom in the nanocluster. The
43
2.3 Hydrogen Evolution Reaction with Metal NC Catalysts
The hydrogen evolution reaction (HER) occurs at the cathode when an external
voltage is applied. The reaction can be described in three steps:
Volmer reaction:
H
+
+ M + e
−
→ MH ads (acidic)
(2.1)
H 2 O + M + e
−
→ MH ads + OH
−
(alkaline)
(2.2)
In the Volmer reaction, hydrogen absorbs on the catalytic material to form a MH ads
intermediate, followed by a Heyrovsky reaction or Tafel reaction. In the Heyrovsky
reaction, the dihydrogen is formed through an electrochemical desorption:
MH ads + H
+
+ e
−
→ M + H 2 (acidic)
(2.3)
MH ads + H 2 O + e
−
→ M + OH
−
+ H 2 (alkaline)
(2.4)
The hydrogen can also undergo a chemical desorption process through the Tafel
reaction:
2 MH ads → 2 M + H 2
(2.5)
The binding energy of hydrogen to the catalyst is the key factor of HER activity.
Among the HER catalysts, noble metals such as Pt and Pd have moderate binding
energy with hydrogen, thus showing excellent HER activities [25]. However, the
high cost and stability issue of Pt catalysts motivate the scientists to find alternative
materials for HER.
Here, we summarize the doping effects and synergetic effects of Au NCs in HER.
We also introduce how the computational technique is used in these cases to explain
differences in catalytic activity and verify proposed mechanisms. These works offer
some insights into the catalytic reactions, which is expected to further pave the way
for future design of catalyst materials.
2.3.1 Pt or Pd Doped Au 25 NCs in HER
The study of Au NCs as HER catalysts was reported by Kyuju et al. in 2017 [26].
A molecular-like Pt 1 Au 24 nanocluster was prepared and used as catalysts in homogeneous HER. Following this work, the same group further studied the Pd 1 Au 24 ,
Pd 2 Au 36 and Pt 2 Au 36 nanoclusters [27]. In the case of Au 25 nanocluster, the doping
atom (Pd or Pt) exclusively replaces the central gold atom in the nanocluster. The