Atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts have exhibited encouraging oxygen reduction reaction (ORR) activity. Nevertheless, the insufficient long-term stability remains a widespread concern owing to the inevitable 2-electron byproducts, H2O2. Here, we construct Co-N-Cr cross-interfacial electron bridges (CIEBs) via the interfacial electronic coupling between Cr2O3 and Co-N-C, breaking the activity-stability trade-off. The partially occupied Cr 3d-orbitals of Co-N-Cr CIEBs induce the electron rearrangement of CoN4 sites, lowering the Co-OOH* antibonding orbital occupancy and accelerating the adsorption of intermediates. Consequently, the Co-N-Cr CIEBs suppress the two-electron ORR process and approach the apex of Sabatier volcano plot for four-electron pathway simultaneously. As a proof-of-concept, the Co-N-Cr CIEBs is synthesized by the molten salt template method, exhibiting dominant 4-electron selectively and extremely low H2O2 yield confirmed by Damjanovic kinetic analysis. The Co-N-Cr CIEBs demonstrates impressive bifunctional oxygen catalytic activity (▵E=0.70 V) and breakthrough durability including 100 % current retention after 10 h continuous operation and cycling performance over 1500 h for Zn-air battery. The hybrid interfacial configuration and the understanding of the electronic coupling mechanism reported here could shed new light on the design of superdurable M-N-C catalysts.

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ZIF-8 derived carbons demonstrate admirable application prospects in electrocatalytic fields, while ZnNx remaining in those materials are overlooked, crippling the validity of theoretic studies in researches. Herein, the residual Zn in ZIF-8 derived carbons are found could exceed 10 wt% even at carbonization temperatures over 900 degrees C, and Zn-NCs with various Zn contents are adopted as supports to synthesize low-platinum ORR catalysts. Substantial characterizations manifest that ZnNx in Zn-NC can not only provide Zn source for L-10-PtZn intermetallic, but act as 'spatial barriers' to prevent the formation of inactive PtNx, elevating the active Pt proportion in catalyst by similar to 104%. The resultant Zn-NC-Ar-PtZn exhibits a mass activity of 0.557 mA/g(Pt) and a peak density of 1.485 W/cm(2). DFT calculations show the strong thermodynamic tendency of forming PtN4 without the protection of ZnN4, and the superior durability and activity of Zn-NC-Ar-PtZn should be attributed to its Zn-derived ligand effects and the SMSI.

Proton exchange membrane fuel cells (PEMFCs) have been identified as a highly promising means of achieving sustainable energy conversion. A crucial factor in enhancing the performance of PEMFCs for further potential energy applications is the advancement in the field of catalyst engineering that has led to remarkable performance enhancement in facilitating the oxygen reduction reaction (ORR). Subsequently, it is important to acknowledge that the techniques used in preparation of membrane electrode assemblies (MEAs), the vital constituents of PEMFCs, also possess direct and critical influence on exhibiting the full catalytic activity of meticulously crafted catalysts. Here, a succinct summary of the most recent advancements in Pt catalysts for ORR was offered and their underly catalytic mechanism were discussed. Then, both laboratory-scale and industrial-scale MEA fabrication techniques of Pt catalysts were summarized. Furthermore, a detailed analysis of the connections between materials, process, and performance in MEA fabrication was presented in order to facilitate the development of optimal catalyst layers.

Alloying platinum with other 3d transition metals (M) in an organized manner is a proven method to enhance the activity and lifespan of Pt catalysts utilized in proton exchange membrane fuel cells (PEMFC). Herein, a distinct composite has been engineered, featuring structured Pt-Fe intermetallic compounds (L12Pt3Fe NPs) supported on an iron-doped sulfur-nitrogen-carbon (Fe-SNC) support. The L12Pt3FeNPs function as the primary catalytic core for the oxygen reduction reaction (ORR) instead of the conventional Pt NPs. The sulfur atom on the Fe-SNC can secure L12Pt3Fe NPs to prevent their aggregation during elevated temperature and operational phases. Additionally, the presence of S atoms can regulate the electronic configuration of platinum and decrease the bond strength between Pt and oxygen-containing intermediates. Consequently, the L12Pt3Fe/Fe-SNC catalyst demonstrates exceptional catalytic efficiency and longevity for ORR with E1/2 of 0.911 V as well as a mass activity (MA) of 0.47 A/mgPt. The L12Pt3Fe/Fe-SNC maintains outstanding ORR stability (MA form 0.47 A/mgPt to 0.38 A/mgPt) after 30,000 cycles of AST. Impressively, the L12Pt3Fe/Fe-SNC has a power density of 1.547 W/ cm2 center dot H2-O2 and 0.669 W/cm2 center dot H2-Air at 0.4 V (cathode Pt loading: 0.04mgPt/cm2) better than commercial Pt/C in PEMFC single-cell. This work provides new ideas for constructing various PtM intermetallic catalysts.

Proton exchange membrane fuel cells (PEMFCs) have been widely acknowledged as a significant advancement in achieving sustainable energy conversion. However, the activation of newly established Pt-ionomer interfaces in the catalyst layer of PEMFCs can be a time-consuming and costly process to ensure proper coupling and performance. In order to gain valuable insights into this crucial activation process, we have conducted a comprehensive analysis and comparison of the commonly employed on-line (such as current or voltage control activation, short-circuiting activation, and air interruption activation) and off-line (including boiling or steaming, acid-treatment, and ultrasonic-treatment) activation methods. Our findings shed light on the underlying mechanisms that contribute to enhanced performance within the catalyst layer, such as the reduction of Pt oxides and hydroxides, improved proton transport, and the reduction of “dead” regions. Moreover, this review emphasizes the significant challenges and future opportunities that lie in further enhancing the performance within the catalyst layer through the activation process.

The main group metals are commonly perceived as catalytically inert in the context of oxygen reduction reactions (ORR) due to the delocalized valence orbitals. Regulating the local environment and structure of metal center coordinated by nitrogen ligands (M-Nx) is a promising approach to accelerate catalytic dynamics. Herein, we, for the first time, report the atomically dispersed Al catalysts coordinated with N and C atoms for 4-electron ORR. The axial coordinated pyrrolyl N group (No) is constructed in the Al-N4-No moiety to regulate the p-band structure of Al center, effectively steering the local environment and structure of the square planar Al-N4 sites, which typically exhibit too strong interaction with ORR intermediates. The dynamic covalency competition of axial Al-No and Al-O bonding could endow the Al center with moderate hybridization between Al 3p orbital and O 2p orbital, alleviating the binding energy of ORR intermediates. The as-prepared Al-N4-No electrocatalyst exhibits excellent ORR activity, selectivity, and durability, along with the rapid kinetics as demonstrated by in situ Raman spectroscopy. This work offers a fundamental comprehension of the fine regulation on p-band and guides the rational design of main-group metal-based single atom catalysts.

Fe-N-C catalyst for oxygen reduction reaction (ORR) has been considered as the most promising nonprecious metal catalyst due to its comparable catalytic performance to Pt in proton exchange membrane fuel cells (PEMFCs). The active centers of Fe-pyrrolic N4 have been proven to be extremely active for ORR. However, forming a stable Fe-pyrrolic N4 structure is a huge challenge. Here, a Cyan-Fe-N-C catalyst with Fe-pyrrolic N4 as the intrinsic active center is constructed with the help of axial Fe4 C atomic clusters, which shows a half-wave potential of up to 0.836 V (vs. RHE) in the acid environment. More remarkably, it delivers a high power density of 870 and 478 mW cm-2 at 1.0 bar in H2 -O2 and H2 -Air fuel cells, respectively. According to theoretical calculation and in situ spectroscopy, the axial Fe4 C can provide strong electronic perturbation to Fe-N4 active centers, leading to the d-orbital electron delocalization of Fe and forming the Fe-pyrrolic N4 bond with high charge distribution, which stabilizes the Fe-pyrrolic N4 structure and optimizes the OH* adsorption during the catalytic process. This work proposes a new strategy to adjust the electronic structure of single-atom catalysts based on the strong interaction between single atoms and atomic clusters.

The effective transport of proton and reactant within the electrode is heavily influenced by the pore structure of the carbon support hosting both Pt particles and ionomers. To this end, the impact of carbon structure on the Pt position, ionomer distribution, and voltage losses under various relative humidity (RH) conditions has been systematically investigated. The findings reveal that low-loading solid carbon-based catalysts display impressive performance at low RH, while high-loading porous carbon-based catalysts stand out at high RH. Furthermore, porous carbon-based catalysts exhibit high mass activity at low current density due to their reduced susceptibility to the poisonous effects of sulfonate groups. Meanwhile, solid carbon catalysts facilitate a more uniform ionomer thin-film and create a more active three-phase interface area, resulting in a satisfactory performance at the high current density region and low local-O2 transport resistance.

Improving the activity and durability of Pt electrocatalysts is an important pathway to reduce the dosage of precious Pt for proton exchange membrane fuel cells (PEMFCs). Herein, zeolitic imidazolate framework-8 (ZIF-8) derived nitrogen-doped carbon (NC) supported Pt-CeO2 composites with abundant triple-phase interfacial conjunction are demonstrated. The CeO2 can modulate the electronic structure of Pt via electronic effects, thus modulating the energy of oxygen intermediates absorbed on Pt sites. Besides, the CeO2 also can stabilize the Pt nanoparticles by metal-support interactions. Therefore, the as-fabricated catalyst shows ultrahigh activity and durability towards oxygen reduction reaction. The half-wave potential is 0.922 V, and mass activity is 0.165 mA.ug(Pt)(-1) in 0.1 M HClO4. After 10, 000 cycles of accelerated durability tests (ADTs), the E-1/2 decreases by only 10 mV. In addition, the 20% Pt/CeO2-NC (power density: 1.08 W.cm(-2), cathode: 0.20 mgPt.cm(-2)) shows more excellent electrochemical activity and durability with lower cathode Pt loading than 20% commercial Pt/C (power density: 1.03 W.cm(-2), cathode: 0.40 mgPt.cm(-2)) in PEMFC single cell measurements. This study provides a novel strategy for constructing a Pt-metal oxide-support triple-phase interface to improve the electrocatalytic performance of catalysts.

Iron and nitrogen co-doped carbon (Fe-N-C) electrocatalysts have great potential to catalyze the kinetically slow oxygen reduction reaction (ORR). Unfortunately, the ORR performances of existing Fe/N/C catalysts is seriously hindered by the poor accessibility and inherent activity of the atomic Fe-Nx moieties. Herein, a carboxylate (OAc) molecular scissor is proposed to tailor Fe doped zeolitic-imidazolate-framework-8 (ZIF-8) at atomic scale and construct hierarchical architecture. This molecular scissoring strategy imparts Fe/N/C-OAc with dense accessible active sites, multidimensional mass transfer pathways, hierarchical porous structure and entangled carbon nanotubes network. Therefore, the tailored Fe/N/C-OAc electrocatalyst exhibits excellent ORR activity in acidic media with a half-wave potential of 0.838V, which is comparable to state-of-the-art non-precious metal catalysts. When assembled as cathode catalyst in a H2-O 2 proton exchange membrane fuel cell, it delivers a peak power density of 0.74Wcm-2 . This work provides a new approach for tailoring catalyst architecture and accessibility of active sites.

Platinum group metal (PGM)-free catalysts represented by nitrogen and iron co-doped carbon (Fe-N-C) catalysts are desirable and critical for metal-air batteries, but challenges still exist in performance and stability. Here, cerium oxides (CeOx) are incorporated into a two-dimensional Fe-N-C catalyst (FeNC-Ce-950) via a host-guest strategy. The Ce4+/Ce3+ redox system creates a large number of oxygen vacancies for rapid O2 adsorption to accelerate the kinetics of oxygen reduction reaction (ORR). Consequently, the as-synthesized FeNC-Ce-950 catalyst exhibits a half-wave potential (E1/2) of 0.921 V and negligible decay (<2 mV for ΔE1/2) after 5,000 accelerated durability cycles, significantly outperforming most of ORR catalysts reported in recent years and precious metal counterparts. When applied in a zinc-air battery, it demonstrates a peak power density of 175 mW cm-2 and a specific capacity of 757 mAh gZn-1. This study also provides a reference for the exploration of Fe-N-C catalysts decorated with variable valence metal oxides.

High-performance platinum nanoparticle catalysts (Pt-NPCs) remain the most widespread applied electrocatalysts for oxygen reduction reaction (ORR). Here, cetyltrimethylammonium bromide (CTAB), a surface-controlling agent, is introduced to modulate the microstructure and size of Pt nanoparticles (NPs) via a microwave-assisted heating process. The Pt-NPC assisted by 5 wt% CTAB exhibits the highest mass activity (MA) of 0.072 A mgPt-1 and specific activity (SA) of 0.077 mA cm-2, higher than those of commercial Pt/C (0.023 A mgPt-1 and 0.035 mA cm-2). Transmission electron microscopy (TEM) results indicate that Pt NPs are uniformly dispersed onto carbon supports with an average size of 2.39 nm. When applied in membrane electrode assembly (MEA), it exhibits the highest power density of 1.142 W cm-2, which is about 1.24 times larger than that of commercial Pt/C. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Carbon supports for cathodic catalysts in proton-exchange membrane fuel cells suffer from rapid corrosion and instability; therefore, alternative supports with a stable structure and a high electric conductivity are highly required. In this paper, a three-dimensional support hybridized by MXene and Ketjen Black is developed, in which Ketjen Black is sandwiched between MXene nanosheets (MCM). After decorating with Pt nanoparticles by a facile wet-chemical approach, a three-dimensional (3D) Pt/MCM catalyst is obtained. The intercalated Ketjen Black prevents the stacking of MXene nanosheets, thus increasing the specific surface area of the catalyst and exposing the active sites. The strong interaction between functionalized MXene nanosheets and Pt nanoparticles further enhances its intrinsic electrocatalytic activity. Pt/MCM demonstrated encouraging ORR activity with the half-wave potential and specific activity of 0.892 V and 0.377 mA center dot cm-2, respectively, surpassing the state-of-the-art Pt/C catalysts. Especially, Pt/MCM achieves ultrahigh durability with a 1 mV decrease in half-wave potential and a 1.73% decrease in mass activity after an accelerated durability test. Given the performance and structure-activity relationships of Pt/MCM, it holds great potential for various energy and catalysis-related applications.

Developing low-loading Pt-based catalysts possessing glorious catalytic performance can accelerate oxygen reduction reaction (ORR) and hence significantly advance the commercialization of proton exchange membrane fuel cells. In this report, we propose a hybrid catalyst that consists of low-loading sub-3 nm PtCo intermetallic nanoparticles carried on Co-N-C (PtCo/Co-N-C) via the microwave-assisted polyol procedure and subsequent heat treatment. Atomically dispersed Co atoms embedded in the Co-N-C carriers diffuse into the lattice of Pt, thus forming ultrasmall PtCo intermetallic nanoparticles. Owing to the dual effect of the enhanced metal-support interaction and alloy effect, as-fabricated PtCo/Co-N-C catalysts deliver an extraordinary performance, achieving a half-wave potential of 0.921 V, a mass activity of 0.700 A mgPt-1@0.9 V, and brilliant durability in the acidic medium. The fuel cell employing PtCo/Co-N-C as the cathode catalyst with an ultralow Pt loading of 0.05 mg cm-2 exhibits an impressive peak power density of 0.700 W cm-2, higher than that of commercial Pt/C under the same condition. Furthermore, the enhanced intrinsic ORR activity and stability are imputed to the downshifted d-band center and the strengthened metal-support interaction, as revealed by density functional theory calculations. This report affords a facile tactic to fabricate Pt-based alloy composite catalysts, which is also applicable to other alloy catalysts.

Abstract Low‐temperature fuel cells (LTFCs) are considered to be one of the most promising power sources for widespread application in sustainable and renewable energy conversion technologies. Although remarkable advances have been made in the mass activity of catalysts, mass transport impedance needs to be urgently addressed at a well‐designed membrane electrode assembly (MEA) scale. Increasing the loading of electrocatalysts is conducive to prepare thinner and more efficient MEAs owing to the resulting enhanced reactant permeability, better proton diffusion, and lower electrical resistance. Herein, recent progress in high‐loading (≥40 wt.%) Pt nanoparticle catalysts (NPCs) and high‐loading (≥2 wt.%) single‐atom catalysts (SACs) for LTFC applications are reviewed. A summary of various synthetic approaches and support materials for high‐loading Pt NPCs and SACs is systematically presented. The influences of high surface area and appropriate surface functionalization for Pt NPCs, as well as coordination environment, spatial confinement effect, and strong metal‐support interactions (SMSI) for SACs are highlighted. Additionally, this review presents some ideas regarding challenges and future opportunities of high‐loading catalysts in the application of LTFCs.