Strong Electron Coupling from the Sub-Nanometer Pd Clusters Confined in Porous Ceria Nanorods for Highly Efficient Electrochemical Hydrogen Evolution Reaction

Abstract

With the advantage of the high catalytic activity of metal clusters from the abundant uncoordinated metal atoms and the interfacial electron interaction between metal/ metal oxides, metal cluster/metal oxide hybrids have great potential in catalysis and have been attracting more and more attention in recent years. In this work, sub-nanometer sized palladium clusters accommodated into porous ceria were successfully synthesized. The characterizations from highresolution transmission electron microscopy (HRTEM) and extended X-ray absorption fine structure (EXAFS) showed that the synthesized Pd sub-nanoclusters have a size of about 0.5 nm. The Pd clusters confined in CeO 2 pores (donated as Pd NCs@CeO 2 ) showed highly efficient electrocatalytic activity and stability for the hydrogen evolution reaction (HER). The electrochemical results indicated that HER on the Pd clusters presents an onset potential of −0.036 V vs RHE and approximately 100 times higher current density than that from the commercial Pt/ C at the low-potential region. Further insights from density functional theory suggest that the active centers are the subunit of Pd clusters rather than CeO 2 support based on the free energy of absorption for hydrogen atoms (ΔG H* ). Meanwhile, compared to the free Pd nanoclusters, the electron transfer between Pd and O atoms in Pd NC@CeO 2 can effectively modulate the adsorption state of H* on the subunit of the Pd cluster, and this cojoint effect can effectively promote the HER catalytic activity of the composite system. We hope this work can lay the foundation for the application of precious metal nanocluster− transition metal oxide composites in hydrogen energy and other catalysis fields.

Recent Advances of CeO2‐Based Electrocatalysts for Oxygen and Hydrogen Evolution as well as Nitrogen Reduction

“…Chen and coworkers reported that sub-nanometer Pd clusters with the size of 0.55-0.61 nm was confined within porous ceria by hydrothermal and reduction methods to obtain efficient HER catalyst, denoted as Pd NCs@CeO 2 (Figure 12a and 12b). [117] In addition, this metal/metal oxide structure produces electron interactions at the interface, which lays the foundation for its high catalytic activity. In 0.5 M H 2 SO 4 , the polarization curve of Pd NCs@CeO 2 showed that the onset potential of HER was À 0.036 V vs RHE, outperforming commercial Pt/C and Pd/C (Figure 12c).…”

“…Moreover, the metal clusters with unambiguous atom‐packing structures as model catalysts can give deep insights into the structure‐property relationship and catalytic mechanism. Chen and coworkers reported that sub‐nanometer Pd clusters with the size of 0.55–0.61 nm was confined within porous ceria by hydrothermal and reduction methods to obtain efficient HER catalyst, denoted as Pd NCs@CeO 2 (Figure 12a and 12b) [117] . In addition, this metal/metal oxide structure produces electron interactions at the interface, which lays the foundation for its high catalytic activity.…”

“…f) The charge density difference Δ1 of the Pd 4 @CeO 2 model, where the red and blue areas denote the decreased and increased electron densities, respectively. Reproduced with permission from Ref [117]…”

Multiatom Catalysts for Energy‐Related Electrocatalysis

“…In another study, Pd clusters (≈0.5 nm) were uniformly dispersed in the nanopores of CeO 2 nanorods (Pd NCs@CeO 2 , Figure 12f). [ 107 ] Benefiting from the clusters’ tiny size, high dispersion, and strong interaction with CeO 2 support, the Pd NCs@CeO 2 shows excellent HER activity with an onset potential of 36 mV and a current density of 100 times higher than that of commercial Pt/C in 0.5 m H 2 SO 4 (Figure 12g).…”

A Review on Ceo2‐Based Electrocatalyst and Photocatalyst in Energy Conversion

“…Gao et al fabricated sub‐nanometer Pd clusters confined in porous CeO 2 and the electrochemical results of the obtained catalysts show nearly 100 times higher activity HER than Pt/C catalyst at low‐potential region. [ 20 ] The adsorption state of H* on the Pd cluster is effectively modulated by the electron transfer between Pd and O atoms, and then, the conjoint effect promotes the HER catalytic activity.…”