Programming ORR Activity of Ni/NiO_x@Pd Electrocatalysts via Controlling Depth of Surface-Decorated Atomic Pt Clusters

Abstract

Carbon nanotube supported ternary metallic nanocatalysts (NCs) comprising Ni core –Pd shell structure and Pt atomic scale clusters in shell (namely, Ni@Pd/Pt) are synthesized by using wet chemical reduction method with reaction time control. Effects of Pt 4+ adsorption time and Pt/Pd composition ratios on atomic structure with respect to electrochemical performances of experimental NCs are systematically investigated. By cross-referencing results of high-resolution transmission electron microscopy, X-ray diffraction, X-ray absorption, density functional theoretical calculations, and electrochemical analysis, we demonstrate that oxygen reduction reaction (ORR) activity is dominated by depth and distribution of Pt clusters in a Ni@Pd/Pt NC. For the optimum case (Pt 4+ adsorption time = 2 h), specific activity of Ni@Pd/Pt is 0.732 mA cm –2 in ORR. Such a value is 2.8-fold higher as compared to that of commercial J.M.-Pt/C at 0.85 V (vs reversible hydrogen electrode). Such improvement is attributed to the protection of defect sites from oxide reaction in the presence of Pt clusters in NC surface. When adsorption time is 10 s, Pt clusters tends to adsorb in the Ni@Pd surface. A substantially increased galvanic replacement between Pt 4+ ion and Pd/Ni metal is found to result in the formation of Ni@Pd shell with Pt cluster in the interface when adsorption time is 24 h. Both structures increase the surface defect density and delocalize charge density around Pt clusters, thereby suppressing the ORR activity of Ni@Pd/Pt NCs.

Metal Nanoclusters: New Paradigm in Catalysis for Water Splitting, Solar and Chemical Energy Conversion

“…Bhalothia et al. designed Ni@Pd‐CNT core–shell NPs covered with Pt NCs . In addition to the adsorption of Pt +4 inside the structure of Ni@Pd‐CNTs, the Pt content on the surface and the role of Pt NCs in catalysis were also monitored.…”

“…signed Ni@Pd-CNT core-shell NPs covered with Pt NCs. [217] In addition to the adsorption of Pt + 4 inside the structure of Ni@Pd-CNTs, the Pt contento nt he surface and the role of Pt NCs in catalysis were also monitored.A st he adsorption time is changed, the charged ensity distribution aroundt he Pt NCs and its intercalation also changes.H owever,t he highest specific surfacea ctivity (0.732 Acm À2 )f or 12 %P tc ontent was observed when the adsorption time was increased to 2h.B oth theoretical and experimental studies revealed that the charge distribution around the Pt NCs inside and over the core-shell structure was helpful to optimize the oxophilic nature of the overall architecture for improved catalytic performance.…”

Atomic Pt-Clusters Decoration Triggers a High-Rate Performance on Ni@Pd Bimetallic Nanocatalyst for Hydrogen Evolution Reaction in Both Alkaline and Acidic Medium

“…Based on the aforementioned arguments and in line with recent developments, in the present study, we synthesized a ternary NC comprising hierarchical Ni@Pd NC with Pt-clusters decoration on the surface via a "self-aligned" heterogeneous nucleation-crystal growth mechanism on carbon black support (namely Ni@Pd-Pt). Our previous studies demonstrated that Pt-clusters decoration effectively shelters the catalyst surface from oxidation and creates intense active sites for HER facilitation [26][27][28][29][30][31]. In such a unique structure, Pt-clusters are decorated on the Ni@Pd surface and at the heteroatomic interfaces of Ni-to-Pd; where the ligand effect (due to difference in electronegativity of adjacent atoms) and lattice strain (due to lattice mismatch) plays a key role at the heterogenous interfaces and relocate electrons to the NC surface, hence, the formation of catalytic active sites takes place, which boosts the HER kinetics.…”

Conformational Effects of Pt-Shells on Nanostructures and Corresponding Oxygen Reduction Reaction Activity of Au-Cluster-Decorated NiOx@Pt Nanocatalysts

“…Meanwhile, Pt forms an unconformable shell, which protects the core crystal from corrosion and shares ORR pathways, including O 2 splitting and relocation kinetics of O-atoms, and thus avoids highly energetic intermediates and their associated kinetic penalties. Our previous work demonstrated a facile approach to trigger ORR activity via Pt-decorated core-shell structures [31,32,33,34,35]. Those ternary metallic NCs consisting of lower dosages of Pt showed distinct activity towards ORR facilitation but with reduced fabrication costs.…”