Tailored Lattice Compressive Strain of Pt-Skins by the L12 -Pt3 M Intermetallic Core for Highly Efficient Oxygen Reduction

Inhibiting Demetalation of Fe─N─C via Mn Sites for Efficient Oxygen Reduction Reaction in Zinc-Air Batteries

Demetalation caused by the electrochemical dissolution of metallic Fe atoms is a major challenge for the practical application of Fe─N─C catalysts. Herein, an efficient single metallic Mn active site is constructed to improve the strength of the Fe─N bond, inhibiting the demetalation effect of Fe─N─C. Mn acts as an electron donor inducing more delocalized electrons to reduce the oxidation state of Fe by increasing the electron density, thereby enhancing the Fe─N bond and inhibiting the electrochemical dissolution of Fe. The oxygen reduction reaction pathway for the dissociation of Fe─Mn dual sites can overcome the high energy barriers to direct O─O bond dissociation and modulate the electronic states of Fe─N4 sites. The resulting FeMn─N─C exhibits excellent ORR activity with a high half-wave potential of 0.92 V in alkaline electrolytes. FeMn─N─C as a cathode catalyst for Zn-air batteries has a cycle stability of 700 h at 25 °C and a long cycle stability of more than 210 h under extremely cold conditions at -40 °C. These findings contribute to the development of efficient and stable metal-nitrogen-carbon catalysts for various energy devices.

Integration Construction of Hybrid Electrocatalysts for Oxygen Reduction

There is notable progress in the development of efficient oxygen reduction electrocatalysts, which are crucial components of fuel cells. However, these superior activities are limited by imbalanced mass transport and cannot be fully reflected in actual fuel cell applications. Herein, the design concepts and development tracks of platinum (Pt)-nanocarbon hybrid catalysts, aiming to enhance the performance of both cathodic electrocatalysts and fuel cells, are presented. This review commences with an introduction to Pt/C catalysts, highlighting the diverse architectures developed to date, with particular emphasis on heteroatom modification and microstructure construction of functionalized nanocarbons based on integrated design concepts. This discussion encompasses the structural evolution, property enhancement, and catalytic mechanisms of Pt/C-based catalysts, including rational preparation recipes, superior activity, strong stability, robust metal-support interactions, adsorption regulation, synergistic pathways, confinement strategies, ionomer optimization, mass transport permission, multidimensional construction, and reactor upgrading. Furthermore, this review explores the low-barrier or barrier-free mass exchange interfaces and channels achieved through the impressive multidimensional construction of Pt-nanocarbon integrated catalysts, with the goal of optimizing fuel cell efficiency. In conclusion, this review outlines the challenges associated with Pt-nanocarbon integrated catalysts and provides perspectives on the future development trends of fuel cells and beyond.

Immobilizing Ordered Oxophilic Indium Sites on Platinum Enabling Efficient Hydrogen Oxidation in Alkaline Electrolyte

Addressing the sluggish kinetics in the alkaline hydrogen oxidation reaction (HOR) is a pivotal yet challenging step toward the commercialization of anion-exchange membrane fuel cells (AEMFCs). Here, we have successfully immobilized indium (In) atoms in an orderly fashion into platinum (Pt) nanoparticles supported by reduced graphene oxide (denoted as O-Pt3In/rGO), significantly enhancing alkaline HOR kinetics. We have revealed that the ordered atomic matrix enables uniform and optimized hydrogen binding energy (HBE), hydroxyl binding energy (OHBE), and carbon monoxide binding energy (COBE) across the catalyst. With a mass activity of 2.3066 A mg-1 at an overpotential of 50 mV, over 10 times greater than that of Pt/C, the catalyst also demonstrates admirable CO resistance and stability. Importantly, the AEMFC implementing this catalyst as the anode catalyst has achieved an impressive power output compared to Pt/C. This work not only highlights the significance of constructing ordered oxophilic sites for alkaline HOR but also sheds light on the design of well-structured catalysts for energy conversion.

Controllable Electronic Transfer Tailoring d-band Center via Cobalt-Oxygen-Bridged Ru/Fe Dual-sites for Boosted Oxygen Evolution

Rational tailoring of the electronic structure at the defined active center of reconstructed metal (oxy)hydroxides (MOOH) during oxygen evolution reaction (OER) remains a challenge. With the guidance of density functional theory (DFT), herein a dual-site regulatory strategy is reported to tailor the d-band center of the Co site in CoOOH via the controlled electronic transfer at the Ru─O─Co─O─Fe bonding structure. Through the bridged O2- site, electrons are vastly flowed from the t2g-orbital of the Ru site to the low-spin orbital of the Co site in the Ru-O-Co coordination and further transfer from the strong electron-electron repulsion of the Co site to the Fe site by the Co-O-Fe coordination, which balancing the electronic configuration of Co sites to weaken the over-strong adsorption energy barrier of OH* and O*, respectively. Benefiting from the highly active of the Co site, the constructed (Ru2Fe2Co6)OOH provide an extremely low overpotential of 248 mV and a Tafel slope of 32.5 mV dec-1 at 10 mA cm-2 accompanied by long durability in alkaline OER, far superior over the pristine and Co-O-Fe bridged CoOOH catalysts. This work provides guidance for the rational design and in-depth analysis of the optimized role of metal dual-sites.

Platinum Nanoparticles Bonded with Carbon Nanotubes for High-Performance Ampere-Level All-Water Splitting

Platinum nanoparticles loaded on a nitrogen-doped carbon nanotubes exhibit a brilliant hydrogen evolution reaction (HER) in an alkaline solution, but their bifunctional hydrogen and oxygen evolution reaction (OER) has not been reported due to the lack of a strong Pt-C bond. In this work, platinum nanoparticles bonded in carbon nanotubes (Pt-NPs-bonded@CNT) with strong Pt-C bonds are designed toward ultralow overpotential water splitting ability in alkaline solution. Benefit from the strong interaction between platinum and high conductivity carbon nanotube substrates through the Pt-C bond also the platinum nanoparticles bonded in carbon nanotube can provide more stable active sites, as a result, the Pt-NPs-bonded@CNT exhibits excellent hydrogen evolution in acid and alkaline solution with ultralow overpotential of 0.19 and 0.23 V to reach 1000 mA cm-2, respectively. Besides, it shows superior oxygen evolution electrocatalysis in alkaline solution with a low overpotential of 1.69 V at 1000 mA cm-2. Furthermore, it also exhibits high stability over 110 h against the evolution of oxygen and hydrogen at 1000 mA cm-2. This strategy paves the way to the high performance of bifunctional electrocatalytic reaction with extraordinary stability originating from optimized electron density of metal active sites due to strong metal-substrate interaction.

Multiscale Regulation of Ordered PtCu Intermetallic Electrocatalyst for Highly Durable Oxygen Reduction Reaction

Transforming the Pt-M alloy into an ordered intermetallic is an effective strategy to improve the electrocatalytic activity and stability toward the oxygen reduction reaction (ORR). However, the synthesis of nanosized intermetallics remains challenging. Herein, we report an efficient ORR electrocatalyst, consisting of a monodisperse nanosized PtCu intermetallic on hollow mesoporous carbon spheres (HMCS). As predicted by theoretical calculations, PtCu intermetallics exhibit beneficial electronic structure, with a low theoretical overpotential of 0.33 V and enhanced Cu stability. Resulting from the multiscale modulation of catalyst structure, the O-PtCu/HMCS catalyst delivers a high mass activity of 2.73 A cm-2Pt at 0.9 V and remarkable stability. Identical location transmission electron microscopy (IL-TEM) investigations demonstrate that the rate of carbon corrosion is alleviated on HMCS, which contributes to the long-term durability. This work provides a promising design strategy for an ORR electrocatalyst, and the IL-TEM investigations offer new perspectives for the performance enhancement mechanism.

Optimizing Intermediate Adsorption on Pt Sites via Triple-Phase Interface Electronic Exchange for Methanol Oxidation

For the most commonly applied platinum-based catalysts of direct methanol fuel cells, the adsorption ability toward reaction intermediates, including CO and OH, plays a vital role in their catalytic activity and antipoisoning in anodic methanol oxidation reaction (MOR). Herein, guided by a theoretical mechanism study, a favorable modulation of the electronic structure and intermediate adsorption energetics for Pt active sites is achieved by constructing the triple-phase interfacial structure between tin oxide (SnO2), platinum (Pt), and nitrogen-doped graphene (NG). From the strong electronic exchange at the triple-phase interface, the adsorption ability toward MOR reaction intermediates on Pt sites could be efficiently optimized, which not only inhibits the adsorption of CO* on active sites but also facilitates the adsorption of OH* to strip the poisoning species from the catalyst surface. Accordingly, the resulting catalyst delivers excellent catalytic activity and antipoisoning ability for MOR catalysis. The mass activity reaches 1098 mA mg-1Pt, 3.23 times of commercial Pt/C. Meanwhile, the initial potentials and main peak for CO oxidation are also located at a much lower potential (0.51 and 0.74 V) against commercial Pt/C (0.83 and 0.89 V).

Manipulation of Electronic States of Pt Sites via d-Band Center Tuning for Enhanced Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells

Expediting the torpid kinetics of the oxygen reduction reaction (ORR) at the cathode with minimal amounts of Pt under acidic conditions plays a significant role in the development of proton exchange membrane fuel cells (PEMFCs). Herein, a novel Pt-N-C system consisting of Pt single atoms and nanoparticles anchored onto the defective carbon nanofibers is proposed as a highly active ORR catalyst (denoted as Pt-N-C). Detailed characterizations together with theoretical simulations illustrate that the strong coupling effect between different Pt sites can enrich the electron density of Pt sites, modify the d-band electronic environments, and optimize the oxygen intermediate adsorption energies, ultimately leading to significantly enhanced ORR performance. Specifically, the as-designed Pt-N-C demonstrates exceptional ORR properties with a high half-wave potential of 0.84 V. Moreover, the mass activity of Pt-N-C reaches 193.8 mA gPt-1 at 0.9 V versus RHE, which is 8-fold greater than that of Pt/C, highlighting the enormously improved electrochemical properties. More impressively, when integrated into a membrane electrode assembly as cathode in an air-fed PEMFC, Pt-N-C achieved a higher maximum power density (655.1 mW cm-2) as compared to Pt/C-based batteries (376.25 mW cm-2), hinting at the practical application of Pt-N-C in PEMFCs.

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

Electrocatalysis underpins the renewable electrochemical conversions for sustainability, which further replies on metallic nanocrystals as vital electrocatalysts. Intermetallic nanocrystals have been known to show distinct properties compared to their disordered counterparts, and been long explored for functional improvements. Tremendous progresses have been made in the past few years, with notable trend of more precise engineering down to an atomic level and the investigation transferring into more practical membrane electrode assembly (MEA), which motivates this timely review. After addressing the basic thermodynamic and kinetic fundamentals, we discuss classic and latest synthetic strategies that enable not only the formation of intermetallic phase but also the rational control of other catalysis-determinant structural parameters, such as size and morphology. We also demonstrate the emerging intermetallic nanomaterials for potentially further advancement in energy electrocatalysis. Then, we discuss the state-of-the-art characterizations and representative intermetallic electrocatalysts with emphasis on oxygen reduction reaction evaluated in a MEA setup. We summarize this review by laying out existing challenges and offering perspective on future research directions toward practicing intermetallic electrocatalysts for energy conversions.