Sublayer Stable Fe Dopant in Porous Pd Metallene Boosts Oxygen Reduction Reaction

Abstract

Engineering the morphology and electronic properties simultaneously of emerging metallene materials is an effective strategy for enhancing their performance as oxygen reduction reaction (ORR) electrocatalysts. Herein, a highly efficient and stable ORR electrocatalyst, Fe-doped ultrathin porous Pd metallene (Fe–Pd UPM) composed of a few layers of 2D atomic metallene layers, was synthesized using a simple one pot wet-chemical method and characterized. Fe–Pd UPM was measured to have enhanced ORR activity compared to undoped Pd metallene. Fe–Pd UPM exhibits a mass activity of 0.736 A mgPd –1 with a loss of mass activity of only 5.1% after 10 000 cycles at 0.9 V versus the reversible hydrogen electrode (vs RHE) in 0.1 M KOH solution. Density functional theory (DFT) calculations reveal that the stable Fe dopant in the inner atomic layers of Fe–Pd UPM delivers a much smaller overpotential during O* hydrogenation into OH*. The morphology, porous structure, and Fe doping were verified to have enhanced ORR activity. We believe that the rational design of metallene materials with porous structures and interlayer doping is promising for the development of efficient and stable electrocatalysts.

Atomically Reconstructed Palladium Metallene by Intercalation-Induced Lattice Expansion and Amorphization for Highly Efficient Electrocatalysis

“…The cyclic voltammetry (CV) curves of these catalysts were recorded in 1.0 M KOH solution at a scan rate of 50 mV s –1 . As shown in Figure S10, the N-Pdene/C showed the most positive Pd oxide reduction peak among the catalysts, revealing the strong oxygen affinity of N-Pdene/C. ,, The electrochemical active surface areas (ECSAs) of Pt/C and Pd-based catalysts were determined by underpotentially deposited hydrogen (H upd ) and Pd oxide reduction in 0.1 M HClO 4 electrolyte, respectively (Figure S10b). The ECSA values were calculated to be 69.4, 58.9, 61.0, 54.0, 47.2, 52.5, and 58.8 m 2 g –1 for Pdene/C, H-Pdene/C, N-Pdene/C, C-Pdene/C, S-Pdene/C, Pd/C, and Pt/C, respectively.…”

“…Benefiting from a distinctive electronic structure, platinum (Pt) and its alloys are among the most effective catalysts for diverse energy-related electrocatalytic reactions. − However, the limited supply and high cost of Pt severely impede commercialization of the Pt-based electrocatalysts and widespread implementation of the relevant technologies. Palladium (Pd), a noble metal with an electron difference of only 0.77%, also demonstrates comparable chemical properties. − In contrast to Pt, Pd-based catalysts have more supplies and lower costs, making them promising alternatives to the predominant Pt catalysts for many electrocatalytic reactions, including formic acid oxidation (FAO), ethanol oxidation reaction (EOR), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER). − However, according to the d-band theory, the higher d-band center of Pd (−1.8 eV) relative to that of Pt (−2.3 eV) with respect to the Fermi energy level ( E F ) leads to stronger adsorption behavior of reactants on the surface, resulting in lower activity of Pd in the electrocatalytic processes. , This nonoptimal binding ability and thus catalytic activity call for the development of strategies capable of enhancing the performance of Pd.…”

“…Among them, two-dimensional (2D) morphology demonstrates distinctive electronic, photonic, and surface properties, which substantially enhances its catalytic performance. − As a class of 2D nanomaterials, metallenes are characterized by metallic compositions with atomic thickness and a curved surface, which deliver a distinctive surface–interface effect and ultrahigh atomic utilization originating from the graphene-like 2D structure, exhibiting great potential in electrocatalytic reactions for energy conversion . Most recently, Pd-based metallenes with various metallic dopants have been reported and achieved ORR activity comparable to that of Pt-based catalysts. ,− In addition to altering the morphology, tuning the lattice strain of Pd can further improve its catalytic activity by optimizing the activation energy barrier of the reactants and the adsorption behavior of intermediates during the catalytic process . Recently, nonmetallic atom intercalation, as the effective and straightfoward approach, has been used to tune the lattice strain as well as electronic structure of Pd, which in turn regulates its bonding with reaction intermediates and thus significantly enhances its catalytic activity. − As a typical example, Huang and co-workers reported that PdH 0.43 nanocrystals could deliver higher activity than Pd counterparts when evaluated as electrocatalysts toward MOR .…”

Pd Metallene Aerogels with Single-Atom W Doping for Selective Ethanol Oxidation

“…Two-dimensional (2D) materials have received great interest thanks to the large lateral size, high electronic conductivity, and highly exposed surface active sites. 24,25 Among them, an emerging class of ultrathin 2D nanomaterials, known as metallene, possess atomic-level dimensions and curved microstructures, which increase the accessible active sites and broad applications in sustainable energy conversion. 26−30 In addition, single-atom doping is also an attractive approach to improve the electrocatalytic activity of the catalysts due to high atomic utilization and a tunable electronic structure.…”

“…Recently, self-assembled porous architectures from individual building blocks have triggered tremendous attention. − Particularly, noble metal aerogels (NMAs) involving macroscopic assembly systems represent the most important class of functional nanomaterials with the collective characteristics of noble metal (e.g., high electrical conductivity, excellent catalytic activities, and special plasmonic behavior) and aerogels (e.g., self-supported feature, continuous porous structure, and superior specific surface area), making them of great interest for a wide range of applications such as electrocatalysis and sensing. − Thus, rationally tuning the morphology and electronic properties of building blocks of NMAs offers a promising method to design highly efficient NMAs. Two-dimensional (2D) materials have received great interest thanks to the large lateral size, high electronic conductivity, and highly exposed surface active sites. , Among them, an emerging class of ultrathin 2D nanomaterials, known as metallene, possess atomic-level dimensions and curved microstructures, which increase the accessible active sites and broad applications in sustainable energy conversion. − In addition, single-atom doping is also an attractive approach to improve the electrocatalytic activity of the catalysts due to high atomic utilization and a tunable electronic structure. − Hence, it is appealing to combine metallene with single-atom doping to create single-atom doping metallene building blocks. Assembling them into three-dimensional (3D) nanostructures enables the synthesis of advanced NMAs, which are expected to retain the functions of single-atom doping metallene and inherit the properties of aerogels, thus greatly promoting electrocatalytic performance.…”