The crux of global energy and carbon-emission issues is the replacement of traditional fossil fuels by burgeoning fuel cells (FCs) as well as hydrogen energy technologies. However, the inherently sluggish oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) at the cathode and the massive utilization of costly metal platinum restrict the large-scale commercialization of FCs and the hydrogen energy industry.

In this thesis, a series of catalyst designs of stacked multimetal/metaloxide core-shell-type structure with local modification of surface decoration or interface intercalation is proposed, aiming at improving the ORR/HER activity, increasing the durability and reducing the Pt usage based on the density functional theory (DFT) calculations, where some ideas are sparked from our previous experimental observation and thus having high feasibility of experimental preparation.

First, we proposed a Cocore@Pdshell configuration decorated with Pt-dimer cluster (i.e., Co@Pd-Pt₂ model surface) to thoroughly explore the effect of embedded Pt dimer on the ORR performance for the metallic nanocatalyst. Our results exhibit that the Pt dimer tunes the local physical and chemical properties of the catalyst surface to generate a unique gradient distribution of adsorption energy (E_ads) corresponding to O₂, O*, H₂O and OH, thus driving the ORR along a specific efficient pathway. The calculated reaction barriers of the two ORR sub-stages and the deep-going charge analysis for the Co@Pd-Pt₂ and other reference catalysts confirm a local catalytic collaboration between the Pt dimer and neighboring Pd/Co on the prominent ORR activity. The decorated Pt dimer in the Co@Pd-Pt₂ system is believed to serve as a charge transfer hub to build a hyper channel for charge exchange between Pd/Co and external ORR-intermediates.
Based on the above result on the Pt dimer-decorated Co@Pd catalyst, we then comprehensively study the effect of the decorated Pt-cluster size (from single-atom to full coverage) on the ORR efficiency of the Co_core-Pd_shell structure. Our results reveal that there is a gradually enhancing synergetic effect on the Pt-Pd interface domains of the surface with the Pt cluster size reduced from nanometers to sub-nanometers, which induces an oriented and tunable charge transfer mechanism from deep-Co to outermost-Pt, thereby optimizing the bonding strength of oxygen and achieving the progressively improved ORR performance with minimum Pt usage and ultrahigh Pt atom utilization (i.e., Pt₁ to Pt₃). Such a dependency between the surface decoration size and ORR activity of the proposed Co@Pd-Pt_n system can be a precise guideline for the ordered heterogeneous nanocatalysts synthesis toward low Pt, high efficiency and green economy.

Thirdly, a novel Pt-free catalyst consisting of interfacial atomic Ni ensemble intercalation in a NiO₂-to-Pd heterostructure, i.e., the NiO₂‒Ni_d‒Pd systems, is modeled for the HER investigation according to our previous experimental observations. Our results indicate that the adsorption energy and Gibbs free energy of atomic hydrogen, i.e., E_ads-H* and ΔG_H*, of the proposed seven NiO₂‒Ni_d‒Pd systems forecast the superior HER activity to Pd(111) and benchmark Pt(111). The transition-state calculations prove the 4-Ni tetragon internally intercalated NiO₂‒Ni₄‒Pd catalyst is the Ni doping threshold in Pd-layers of the NiO₂‒Ni_d‒Pd series in terms of the HER kinetic improvement. Deep insight into the charge distribution reveals that the optimal HER performance observed on the representative NiO₂‒Ni₄‒Pd is attributed to the synergistic effect triggered by ligand and strain effect from the internally doped Ni tetragon and its surrounding Pd atoms, leading to the electron disequilibrium on the local domain of the surface with invariable the atomic arrangement of the surface.

Finally, the Ir oxide cluster-decorated Co₃O₄@Pd core-shell catalyst (namely, the CPI-1, CPI-3 and CPI-7 models) are developed based on our experimental observation. The results provide concrete evidence that the anchored IrO₃ monomer is observed to regulate the Eads of the key adsorbates (O₂, O*, H₂O and OH) of the entire surface, thereby, the differentiated Eads-distribution for different absorbates on catalyst surface were generated, which make the near-IrO₃-zone more suitable for O₂ dissociation and the far-off Pd-zone more preferable for subsequent O* reduction. In-depth electron localization function (ELF) reveal a confinement effect developing a strong negative field around the atomic IrO₃ to repel the negatively charged O* and OH*, facilitate O* relocation and regenerate the active sites in the near-IrO₃-zone for ORR. Such a scenario endows the optimal CPI-1 catalyst a unique ORR mechanism with the simultaneous collaboration of the various intermediate steps in ORR across the various segmented surface zones, therefore, rationalizing the IrO₃ monomer as a single nanoparticle reactor with ultra-high performance in ORR.