Comparison between the Oxygen Reduction Reaction Activity of Pd5Ce and Pt5Ce: The Importance of Crystal Structure

Strain Engineering of Unconventional Crystal-Phase Noble Metal Nanocatalysts

The crystal phase, alongside the composition, morphology, architecture, facet, size, and dimensionality, has been recognized as a critical factor influencing the properties of noble metal nanomaterials in various applications. In particular, unconventional crystal phases can potentially enable fascinating properties in noble metal nanomaterials. Recent years have witnessed notable advances in the phase engineering of nanomaterials (PEN). Within the accessible strategies for phase engineering, the effect of strain cannot be ignored because strain can act not only as the driving force of phase transition but also as the origin of the diverse physicochemical properties of the unconventional crystal phase. In this review, we highlight the development of unconventional crystal-phase noble metal nanomaterials within strain engineering. We begin with a short introduction of the unconventional crystal phase and strain effect in noble metal nanomaterials. Next, the correlations of the structure and performance of strain-engineered unconventional crystal-phase noble metal nanomaterials in electrocatalysis are highlighted, as well as the phase transitions of noble metal nanomaterials induced by the strain effect. Lastly, the challenges and opportunities within this rapidly developing field (i.e., the strain engineering of unconventional crystal-phase noble metal nanocatalysts) are discussed.

Room-Temperature Synthesis of Sub-2 nm Ultrasmall Platinum-Rare-Earth Metal Nanoalloys for Hydrogen Evolution Reaction

To tune the activity of Pt alloy electrocatalysts and reduce the Pt loading, researchers have intensively studied alloys of Pt with late transition metals. However, Pt alloy formation with rare-earth (RE) elements through the traditional chemical route is still a challenge due to the vastly different standard reduction potentials. Here, we report a universal chemical method to prepare a series of Pt/RE (RE = La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Lu) nanoalloys with tunable compositions and ultrasmall particle sizes (sub-2 nm). These Pt-RE nanoalloys were synthesized by a strong liquid metal reduction with high-speed shearing assistance at room temperature. Among the nine Pt-RE alloy catalysts, the PtNd/C shows the best hydrogen evolution reaction (HER) activity, stability, and durability compared to commercial Pt/C. The PtNd/C shows an overpotential of 25.9 mV at the current density of 10 mA/cm² with a Tafel slope of 19.5 mV/dec and excellent stability in the acidic medium. This work not only provides a general and scalable strategy for synthesizing noble metal-RE alloys but also highlights noble metal-RE alloys as sufficiently advanced catalysts and accelerates the research of noble metal-RE alloy in energy-related applications.

Pt-Free Metal Nanocatalysts for the Oxygen Reduction Reaction Combining Experiment and Theory: An Overview

The design and manufacture of highly efficient nanocatalysts for the oxygen reduction reaction (ORR) is key to achieve the massive use of proton exchange membrane fuel cells. Up to date, Pt nanocatalysts are widely used for the ORR, but they have various disadvantages such as high cost, limited activity and partial stability. Therefore, different strategies have been implemented to eliminate or reduce the use of Pt in the nanocatalysts for the ORR. Among these, Pt-free metal nanocatalysts have received considerable relevance due to their good catalytic activity and slightly lower cost with respect to Pt. Consequently, nowadays, there are outstanding advances in the design of novel Pt-free metal nanocatalysts for the ORR. In this direction, combining experimental findings and theoretical insights is a low-cost methodology—in terms of both computational cost and laboratory resources—for the design of Pt-free metal nanocatalysts for the ORR in acid media. Therefore, coupled experimental and theoretical investigations are revised and discussed in detail in this review article.

Lattice-Strain Engineering of Homogeneous NiS0.5 Se0.5 Core-Shell Nanostructure as a Highly Efficient and Robust Electrocatalyst for Overall Water Splitting

Developing highly-efficient non-noble-metal electrocatalysts for water splitting is crucial for the development of clean and reversible hydrogen energy. Introducing lattice strain is an effective strategy to develop efficient electrocatalysts. However, lattice strain is typically co-created with heterostructure, vacancy, or substrate effects, which complicate the identification of the strain-activity correlation. Herein, a series of lattice-strained homogeneous NiS_x Se_{1- x} nanosheets@nanorods hybrids are designed and synthesized by a facile strategy. The NiS_0.5 Se_0.5 with ≈2.7% lattice strain exhibits outstanding activity for hydrogen and oxygen evolution reaction (HER/OER), affording low overpotentials of 70 and 257 mV at 10 mA cm^-2 , respectively, as well as excellent long-term durability even at a large current density of 100 mA cm^-2 (300 h), significantly superior to other benchmarks and the precious metal catalysts. Experimental and theoretical calculation results reveal that the generated lattice strain decreases the metal d-orbital overlap, leading to a narrower bandwidth and a closer d-band center toward the Fermi level. Thus, NiS_0.5 Se_0.5 possesses favorable H* adsorption kinetics for HER and lower energy barriers for OER. This work provides a new insight to regulate the lattice strain of advanced catalyst materials and further improve the performance of energy conversion technologies.