Abstract
Efficient and durable electrocatalysts are essential for hydrogen related energy technologies, including water electrolysis and fuel cells. However, catalyst performance is determined not only by composition, but also by local coordination, interfacial structure, and dynamic evolution under operating conditions. This dissertation investigates how atomic and nanoscale structural design can regulate catalyst working states and improve electrocatalytic activity for alkaline hydrogen evolution reaction and acidic oxygen reduction reaction.
In Chapter 2, single atom Mo doped NiO nanoparticles are developed for alkaline HER. In situ X-ray absorption spectroscopy and Raman spectroscopy reveal that Mo single atoms remain structurally stable while promoting the transformation of NiO into a hydroxylated Ni(OH)2 containing working phase under HER bias. This demonstrates that isolated Mo atoms act as structural and electronic triggers for active-phase formation rather than simply serving as additional adsorption sites.
In Chapter 3, Co–Mo oxide nanoparticles with distinct Mo incorporation modes are investigated to clarify how dopant structure affects alkaline HER activity. The Mo free, low Mo, and high Mo samples are assigned to Co3O4, single atom Mo-Co3O4, and amorphous or poorly crystalline heterogeneous CoOx/CoMoO4, respectively. Among them, CoOx/CoMoO4 shows the best HER performance, requiring only 50 mV at 10 mA/cm2 and 171 mV at 100 mA/cm2 in 1 M KOH. In situ XANES, EXAFS, and Raman spectroscopy reveal that CoOx/CoMoO4 undergoes lower overpotential Co reduction, Co–Co coordination formation, and Co–O bond weakening, while Mo K-edge XAS indicates partial Mo reduction and possible formation of reduced Mo containing or Co–Mo alloy like active motifs. These results show that heterogeneous CoOx/CoMoO4 interface engineering is more effective than isolated Mo doping by promoting reconstruction into a Co-rich, Mo-involved active state.
In Chapter 4, ordered Cu3Pt nanocages are investigated as atom efficient Pt based ORR catalysts. Cu/Cu3Pt precursor particles are converted into hollow Cu3Pt nanocages with an ordered L12 intermetallic shell. Microscopy and XAS confirm that Pt remains incorporated within a Cu-rich ordered framework rather than segregating into Pt rich domains. This structure combines electronic modulation from Cu–Pt interactions with enhanced Pt utilization from the hollow nanocage morphology, leading to improved ORR activity relative to commercial Pt/C.
Overall, this dissertation establishes three complementary design strategies for electrocatalysts: single atom modulation, heterointerface enabled reconstruction, and ordered intermetallic atom efficient architecture. Across these systems, in situ and operando spectroscopy identify the true working states responsible for activity, highlighting the importance of designing catalysts according to how their structures evolve under realistic electrochemical conditions.
