Transition Metal Nitride Coated with Atomic Layers of Pt as a Low-Cost, Highly Stable Electrocatalyst for the Oxygen Reduction Reaction

Titanium nitride meta-biosensors targeting extracellular vesicles for high-sensitivity prostate cancer detection

Disposable plasmonic metasurfaces with high biosensing performance are urgently sought for clinical label-free detection. Low-cost aluminum (Al) and titanium nitride (TiN) offer promising alternatives to noble metals for constructing these metasurfaces. However, Al suffers from limited chemical stability, and TiN exhibits weak plasmonic effects, both of which hinder their application in meta-biosensing. Here we integrate their complementary advantages and propose the TiN/Al meta-biosensors. They not only empower the unique near-field enhancement for sensing by TiN/Al hybrid plasmonic modes, but also construct a robust TiN armor against external wear, heat, moisture and corrosion during the bio-detection process. Compared to traditional gold-based counterparts, our meta-biosensors offer superior optical sensitivity at a much lower cost and with fewer pretreatment steps. The excellent biosensing performance facilitates the development of a high-throughput detection system for serum small extracellular vesicles (sEVs), aiding in the diagnosis and follow-up of prostate cancer. The sEVs meta-biosensing demonstrates a diagnostic sensitivity of 100% for significantly distinguishing early cancer, breaking through the conventional testing limitation. Moreover, it doubles the prediction accuracy of cancer recurrence risk following surgery. Our research highlights the potential for large-scale development of powerful meta-biosensors based on non-noble materials, opening up significant opportunities in cancer diagnosis and prognosis.

Porous Tungsten Nitride: A Sensitive SERS Substrate with High Stability

In surface-enhanced Raman spectroscopy detection, the structure of the Raman scattering substrate is critical to the sensitivity and stability of the detector. In this study, W18O49 ultrafine nanowire bundles are used as precursors to synthesize porous tungsten nitride (WN) through a nitriding treatment. As a typical transition metal nitride (TMN), these porous WN exhibit a strong localized surface plasmon resonance effect in the visible region, with a resonance peak centered at 672 nm. Significantly, WN as a substrate for detection of typical dyes exhibit strong Raman enhancement signals. In particular, the detection sensitivity for R6G has been significantly improved, with the lowest detectable concentration reaching an impressive 1 × 10-10 M, and the maximum enhancement factor is up to 1.62 × 107. Moreover, they even can maintain the detection performance in a variety of harsh environments, showing outstanding corrosion resistance, and oxidation resistance, which is not available on traditional noble metal and semiconductor Raman substrates.

Combining a Pd Cluster and a Built-in Electric Field as a Biomimic for Stable C-Cl Bond Polarization

Adopting the essence of enzyme catalysis, the strong binding of substrates into the active site pocket for their selective activation through multiple noncovalent interactions in the reactive site design can effectively enhance the electrocatalysis process. However, mimicking the enzyme catalytic process, particularly the introduction of reactant activation mechanisms, remains a significant challenge. Herein, we present a Pd cluster inside the Fe2N-Fe3O4-based built-in electric field (BEF), denoted as Pd/Fe2N-Fe3O4, to serve as an enzyme mimic to activate stable C-Cl bonds. Theoretical calculations and in situ Raman indicate that the probe molecule 2,4-dichlorophenol (2,4-DCP) adsorbs onto the Pd site and rotates inside the BEF with the C4-Cl bond being selectively activated and elongated from 1.73 to 1.82 Å. This makes Pd/Fe2N-Fe3O4 an excellent electrocatalytic hydrodechlorination catalyst, with Pd usage down to 2.5 μg cm-2, which is 32.7-360 times less than that of conventional catalysts like Pd/C, and achieving a Faradaic efficiency exceeding 20%. We reveal that besides H*-mediated electrochemical reduction, Pd/Fe2N-Fe3O4 also hydrodechlorinates activated 2,4-DCP via the proton-electron coupled transfer pathway. This understanding of the role of BEF in reactant activation, along with the strategy of integrating BEF and noble metals to mimic enzymes, provides a direction for the design of advanced electrocatalysts.

Deactivation Mechanism and Mitigation Strategies of Single-Atom Site Electrocatalysts

Single-atom site electrocatalysts (SACs), with maximum atom efficiency, fine-tuned coordination structure, and exceptional reactivity toward catalysis, energy, and environmental purification, have become the emerging frontier in recent decade. Along with significant breakthroughs in activity and selectivity, the limited stability and durability of SACs are often underemphasized, posing a grand challenge in meeting the practical requirements. One pivotal obstacle to the construction of highly stable SACs is the heavy reliance on empirical rather than rational design methods. A comprehensive review is urgently needed to offer a concise overview of the recent progress in SACs stability/durability, encompassing both deactivation mechanism and mitigation strategies. Herein, this review first critically summarizes the SACs degradation mechanism and induction factors at the atomic-, meso- and nanoscale, mainly based on but not limited to oxygen reduction reaction. Subsequently, potential stability/durability improvement strategies by tuning catalyst composition, structure, morphology and surface are delineated, including construction of robust substrate and metal-support interaction, optimization of active site stability, fabrication of porosity and surface modification. Finally, the challenges and prospects for robust SACs are discussed. This review facilitates the fundamental understanding of catalyst degradation mechanism and provides efficient design principles aimed at overcoming deactivation difficulties for SACs and beyond.

Recent Advances in MOF-Based Materials for Biosensing Applications

Metal-organic frameworks (MOFs) or coordination polymers have gained enormous interest in recent years due to their extraordinary properties, including their high surface area, tunable pore size, and ability to form nanocomposites with various functional materials. MOF materials possess redox-active properties that are beneficial for electrochemical sensing applications. Furthermore, the tunable pore size and high surface area improve the adsorption or immobilization of enzymes, which can enhance the sensitivity and selectivity for specific analytes. Additionally, MOF-derived metal sulfides, phosphides, and nitrides demonstrate superior electrical conductivity and structural stability, ideal for electrochemical sensing. Moreover, the functionalization of MOFs further increases sensitivity by enhancing electrode-analyte interactions. The inclusion of carbon materials within MOFs enhances their electrical conductivity and reduces background current through optimized loading, preventing agglomeration and ensuring uniform distribution. Noble metals immobilized on MOFs offer improved stability and catalytic performance, providing larger surface areas and uniform nanoparticle dispersion. This review focuses on recent developments in MOF-based biosensors specifically for glucose, dopamine, H2O2, ascorbic acid, and uric acid sensing.

Designed synthesis of multi-defective Ti0.9Cu0.1N@Pt as a robust catalyst for the oxygen reduction reaction

Proton-exchange membrane (PEM) fuel cells require cost-effective and robust catalysts capable of withstanding high levels of operation. However, the sluggish cathode oxygen reduction reaction (ORR) and the high cost and instability of the currently used catalysts present significant challenges for the commercialization of PEMFCs. To address these issues, multi-defective Cu-titanium nitride (Ti0.9Cu0.1N) nanospheres with a large surface area are synthesized, and then deposited with a thin layer of Pt, forming a Ti0.9Cu0.1N@Pt catalyst. Compared to commercial Pt/C catalysts, this Ti0.9Cu0.1N@Pt catalyst demonstrates a 53 mV greater half-wave potential in acidic media, indicating its improved ORR performance. Additionally, the Ti0.9Cu0.1N@Pt catalyst can maintain a high mass activity retention of 63% after 6000 accelerating cycle tests, whereas commercial Pt/C catalysts lose 70% of their mass activity. These findings indicate the promising potential for developing and implementing a binary nitride support to enhance Pt utilization in the near future.

Atomic Layer Thickness Modulated the Catalytic Activity of Platinum for Oxygen Reduction and Hydrogen Oxidation Reaction

Reducing platinum (Pt) usage and enhancing its catalytic performance in the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) are vital for advancing fuel cell technology. This study presents the design and investigation of monolayer and few-layer Pt structures with high platinum utilization, developed through theoretical calculations. By minimizing the metal thickness from 1 to 3 atomic layers, an atomic utilization rate ranging from 66.66% to 100% is achieved, in contrast to conventional multilayer Pt structures. This reduction resulted in a unique surface coordination environment. These thinner structures exhibited nonlinear fluctuations in key electronic characteristics-such as the d-band center, surface charge, and work function-as the atomic layer thickness decreased. These variations significantly impacted species adsorption and the Pt-H2O interfacial structure, which in turn affected the catalytic activity. Notably, 1-layer Pt exhibited the best performance for HOR, while 3-layer Pt showed high activity for both HOR and ORR. The findings establish a clear relationship between atomic layer thickness, surface characteristics, adsorption behavior, electric double-layer structure, and catalytic performance in Pt systems. This research contributes to a deeper understanding of precision atomic-structured electrocatalyst design and paves the way for the development of highly effective, low-loading Pt-based catalytic materials.

Oxygen-Doped γ-Mo2N as High-Performance Catalyst for Ammonia Decomposition

γ-Mo2N catalysts exhibit excellent activity and stability in ammonia decomposition reactions. However, the influence of oxygen on its activity is still unknown. In this work, two γ-Mo2N catalysts with different oxygen content are synthesized using temperature-programmed nitridation of α-MoO3. The γ-Mo2N catalysts are highly oxidized and their ammonia decomposition performance is closely related to their oxygen content. The activity of γ-Mo2N with high oxygen content (HO-γ-Mo2N) is much higher, whose H2 formation rate at 550 °C is 3.3 times higher than the γ-Mo2N with low oxygen content (LO-γ-Mo2N). This is mainly attributed to two aspects: on the one hand, the higher valence state of Mo in the HO-γ-Mo2N leads to stronger Mo─NH3 bonds, which promotes the adsorption and activation of NH3. On the other hand, the H generated by N─H bond breaking is more easily migrated to O, which avoids excessive H occupying the γ-Mo2N active sites and alleviates the negative effect of hydrogen poisoning.

Optical and Plasmonic Properties of High-Electron-Density Epitaxial and Oxidative Controlled Titanium Nitride Thin Films

The present paper reports on the fabrication, detailed structural characterizations, and theoretical modeling of titanium nitride (TiN) and its isostructural oxide derivative, titanium oxynitride (TiNO) thin films that have excellent plasmonic properties and that also have the potential to overcome the limitation of noble metal and refractory metals. The TiNO films deposited at 700 °C in high vacuum conditions have the highest reflectance (R = ∼ 95%), largest negative dielectric constant (ε1 = -161), and maximal plasmonic figure of merit (FoM = -ε1/ε2) of 1.2, followed by the 600 °C samples deposited in a vacuum (R = ∼ 85%, ε1 = -145, FoM = 0.8) and 700 °C-5 mTorr sample (R = ∼ 82%, ε1 = -8, FoM = 0.3). To corroborate our experimental observations, we calculated the phonon dispersions and Raman active modes of TiNO by using the virtual crystal approximation. From the experimental and theoretical studies, a multilayer optical model has been proposed for the TiN/TiNO epitaxial thin films for obtaining individual complex dielectric functions from which many other optical parameters can be calculated. The advantages of oxide derivatives of TiN are the continuation of similar free electron density as in TiN and the acquisition of additional features such as oxygen-dependent semiconductivity with a tunable bandgap.

Cyanide Functionalization and Oxygen Vacancy Creation in Ni-Fe Nano Petals Sprinkled with MIL-88A Derived Metal Oxide Nano Droplets for Bifunctional Alkaline Seawater Electrolysis

This work investigates novel improvements in FeNi-layered double hydroxide (LDH)/MIL-88A heterocomposite for sustainable seawater electrolysis through a single-step dual functionalization process. The Fe/Ni precursor weight ratio is optimized, resulting in the formation of smaller LDH petals and nano-sized MIL-88A metal-organic framework, which transforms into clusters of Fe2O3 nanospheres within a nitrogen-functionalized carbon matrix over NiFe2O4 nano petals upon calcination. Furthermore, oxygen vacancies, and nitrogen functionalization are attained in a single step by employing thermal ammonia reduction, significantly improving the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activities. Particularly the oxygen vacancy and nitrogen functionalization are found to accelerate the O─O coupling step in OER by lowering the activation barrier. Likewise, the dual functionalization promotes destabilizing the hydride intermediates in HER potentially facilitating faster proton-coupled electron transfer. Hence, the optimized electrode achieves current densities of 200 mA cm-2 at overpotentials of 350 and 240 mV for OER and HER respectively. The chronopotentiometry stability tests confirms the electrode's durability over 200 h at 20 mA cm-2 in alkaline seawater electrolyte. The optimized electrode, composed of cost-effective and environmentally friendly materials, demonstrates robustness in alkaline seawater electrolytes, positioning it as a strong candidate for practical and sustainable water electrolysis applications.

In-situ construction of N-doped Zn0.6Cd0.4S/oxygen vacancy-rich WO3 Z-scheme heterojunction compound for boosting photocatalytic hydrogen production

Photocatalytic water splitting technology for H2 production represents a promising and sustainable approach to clean energy generation. In this study, a high concentration of oxygen vacancies was introduced into tungsten trioxide (WO3) to create a vacancy-rich layer. This modified WO3 (WO3-x) was then combined with N-doped Zn0.6Cd0.4S through a hydrothermal synthesis, resulting in the formation of a Z-scheme heterojunction composite aimed at enhancing photocatalytic performance. Under visible light, the H2 production activity of the composite reached an impressive 8.52 mmol·g-1 without adding co-catalyst Pt. This corresponds to enhancements of 7.82 and 4.39 times the production yield of pure ZCS and ZCSN, respectively. However, the hydrogen production increased to 21.98 mmol·g-1 when Pt was added as a co-catalyst. Furthermore, an array of characterizations were employed to elucidate the presence of oxygen vacancies and the establishment of the Z-scheme heterojunction. This structural enhancement significantly facilitates the utilization of photo-generated electrons while effectively preventing photo-corrosion of ZCSN, thus improving material stability. Our study provides a new scheme for the incorporation of oxygen-rich vacancy and the construction of Z-scheme heterojunction, demonstrating a synergistic effect that greatly advances photocatalytic performance.

Thermal Migration to Recover Spent Pt/C Catalyst

Recovery of spent Pt/C catalyst is a sustainable low-cost route to promote large-scale application of hydrogen fuel cells. Here, we report a thermal migration strategy to recover the spent Pt/C. In this route, the ZIF-8 is used to produce nitrogen doped porous carbon (NC) with abundant pyrimidine nitrogen sites as the new support. Subsequently, the spent Pt/C, NC, and NH4Cl etching reagent are mixed and heated at 900 °C to thermally migrate Pt from Pt/C onto NC with the help of NH4Cl etching reagent. The thermal-volatilized Pt tends to be captured by the pyrimidine nitrogen sites of NC support, thus producing the Pt clusters or 4-5 nm Pt particles. The recovered Pt/NC catalyst exhibits the highly stable oxygen reduction activities with a mass activity of 0.6 A mgPt -1 after 30000-cycle accelerated durability test.

D-Band-Center-Engineered Platinum-Based Nanozyme for Personalized Pharmacovigilance

A high-efficiency PtZnCd nanozyme was screened with density functional theory (DFT) and unique d-orbital coupling features for sensitive enrichment and real-time analysis of CO-releasing molecule-3 (CORM-3). Multicatalytic sites in the nanozyme showed a high reactivity of up to 72.89 min-1 for peroxidase (POD)-like reaction, which was 2.2, 4.07, and 14.67 times higher than that of PtZn (32.67 min-1), PtCd (17.89 min-1), and Pt (4.97 min-1), respectively. Normalization of the catalytic sites showed that the catalytic capacity of the active site in PtZnCd was 2.962 U μmol-1, which was four times higher than that of a pure Pt site (0.733 U μmol-1). DFT calculations showed that improved d-orbital coupling between different metals reduces the position of the center of the shifted whole d-band relative to the Fermi energy level, thereby increasing the contribution of the sites to the electron transfer from the active center, accompanied by enhanced substrate adsorption and intermediate conversion in the catalytic process. The potential adsorption principle and color development mechanism of CORM-3 on PtZnCd were determined, and its practical application in drug metabolism was validated in vitro and in zebrafish and mice models, demonstrating that transition-metal doping effectively engineers high-performance nanozymes and optimizes artificial enzymes.

Low-valence platinum single atoms in sulfur-containing covalent organic frameworks for photocatalytic hydrogen evolution

This study focuses on optimizing catalytic activity in photocatalytic hydrogen evolution reaction by precisely designing and modulating the electronic structure of metal single atoms. The catalyst, denoted as PtSA@S-TFPT, integrates low-valence platinum single atoms into sulfur-containing covalent organic frameworks. The robust asymmetric four-coordination between sulfur and platinum within the framework enables a high platinum loading of 12.1 wt%, resulting in efficient photocatalytic hydrogen production activity of 11.4 mmol g-1 h-1 and stable performance under visible light. These outcomes are attributed to a reduced hydrogen desorption barrier and enhanced photogenerated charge separation, as indicated by density functional theory calculations and dynamic carrier analysis. This work challenges traditional notions and opens an avenue for developing low-valence metal single atom-loaded covalent organic framework catalysts to advance photocatalytic hydrogen evolution.

Improving the Chemical Utilization Efficiency of Pd Hydrodechlorination Catalysts through Hydrogen-Spillover Empowered Synergy between Pd and TiNiN Support

The sustainable and affordable environmental application of Pd catalysis needs further improvement of Pd mass activity. Besides the well-recognized importance of physical utilization efficiency─the ratio of surface atoms forming reactant-accessible reactive sites─a lesser-known fact is that the congestion of these reactive sites, which we term as the chemical utilization efficiency, also influences the mass activity. Herein, by leveraging the 100% physical utilization efficiency of a fully exposed Pd cluster (Pdn) and the hydrogenation activity of TiNiN, we developed Pdn/TiNiN as a high physical and chemical utilization efficiency catalyst. During the catalytic hydrodechlorination of 4-chlorophenol and the subsequent hydrogenation of phenol, Pdn focuses on H2 dissociation and C-Cl cleavage, while TiNiN facilitates the subsequent hydrogenation of phenol into less toxic cyclohexanone via H-spillover. This synergy results in a 20-40-fold increase in the hydrodechlorination rate. The enhanced chemical utilization efficiency of Pd informs the design of Pdn/TiNiN microspheres for the conversion of halogenated organics from pharmaceutical wastewater and the design of a fixed-bed reactor to transfer trace amounts of 4-CP from river water. Ultimately, this approach decentralizes the use of Pd in environmental catalysis and reduction processes.

Enhanced bifunctional electrocatalysis of Co5.47N nanocrystals in porous carbon nanofibers for high-efficiency zinc-air batteries

As a promising energy conversion and storage device, recently, rechargeable zinc-air batteries (ZABs) have developed rapidly, and the exploitation of excellent electrode catalysts to improve the energy efficiency and long-term performance of ZABs has become a focus of current research. Herein, the Co5.47N nanocrystals embedded in porous carbon nanofibers (Co5.47N PCNFs) were designed to act as a bifunctional electrocatalyst for the oxygen reduction reaction (ORR) and iodide oxidation reaction (IOR), which occur on the electrode in the charging-discharging process of ZABs. The electrochemistry results showed that the ORR activity of Co5.47N PCNFs is comparable to the commercial Pt/C electrocatalyst, and the IOR activity and stability are higher than those of the Pt/C electrocatalyst. Importantly, Co5.47N PCNFs electrocatalyst endows ZABs with a low charge-discharge voltage difference (0.49 V), a high round-trip energy efficiency (72.1 %), as well as a large specific capacity (791.5 mAh gZn-1), surpassing the performance of Pt/C electrocatalyst. Density functional theory calculation demonstrates that Co5.47N PCNFs have lower Gibbs free energy for the formation of IOR intermediate species, thereby displaying outstanding IOR catalytic performance compared to that of Pt/C electrocatalyst. These findings offer crucial insights into the rational design of cobalt nitride-based electrocatalysts for application in ZABs with high energy efficiency.

Molybdenum oxide/nickel molybdenum oxide heterostructures hybridized active platinum co-catalyst toward superb-efficiency water splitting catalysis

A new catalyst has been developed that utilizes molybdenum oxide (MoO3)/nickel molybdenum oxide (NiMoO4) heterostructured nanorods coupled with Pt ultrafine nanoparticles for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) toward industrial-grade water splitting. This catalyst has been synthesized using a versatile approach and has shown to perform better than noble-metals catalysts, such as Pt/C and RuO2, at industrial-grade current level (≥1000 mA·cm-2). When used simultaneously as a cathode and anode, the proposed material yields 10 mA·cm-2 at a remarkably small cell voltage of 1.55 V and has shown extraordinary durability for over 50 h. Density functional theory (DFT) calculations have proved that the combination of MoO3 and NiMoO4 creates a metallic heterostructure with outstanding charge transfer ability. The DFT calculations have also shown that the excellent chemical coupling effect between the MoO3/NiMoO4 and Pt synergistically optimize the charge transfer capability and Gibbs free energies of intermediate species, leading to remarkably speeding up the reaction kinetics of water electrolysis.

Epitaxial Ultrathin Pt Atomic Layers on CrN Nanoparticle Catalysts

The construction of platinum (Pt) atomic layers is an effective strategy to improve the utilization efficiency of Pt atoms in electrocatalysis, thus is important for reducing the capital costs of a wide range of energy storage and conversion devices. However, the substrates used to grow Pt atomic layers are largely limited to noble metals and their alloys, which is not conducive to reducing catalyst costs. Herein, low-cost chromium nitride (CrN) is utilized as a support for the loading of epitaxial ultrathin Pt atomic layers via a simple thermal ammonolysis method. Owing to the strong anchoring and electronic regulation of Pt atomic layers by CrN, the obtained Pt atomic layers catalyst (containing electron-deficient Pt sites) exhibits excellent activity and endurance for the formic acid oxidation reaction, with a mass activity of 5.17 A mgPt -1 that is 13.6 times higher than that of commercial Pt/C catalyst. This novel strategy demonstrates that CrN can replace noble metals as a low-cost substrate for constructing Pt atomic layers catalysts.

Two-stage confinement derived small-sized highly ordered L10-PtCoZn for effective oxygen reduction catalysis in PEM fuel cells

Intermetallic ordered PtCo is effective for high oxygen reduction reaction (ORR) activity and stability. However, preparing small-sized, highly ordered PtM alloys is still challenging. Herein, we report a controlled two-stage confinement strategy, in which highly ordered PtCoZn/NC nanoparticles of 5.3 nm size were prepared in a scalable process. The contradiction between the high ordering degree with the small particle size as well as the atomic migration with the space confinement was well resolved. An outstanding PEMFC performance was achieved for L10-PtCoZn/NC with a high mass activity (MA) of 1.21 A/mgPt at 0.9 ViR-free, 80.1 % MA retention after 30 k cycles in H2-O2 operation, and a high mass-specific power density of 8.24 W mg-1Pt in H2-Air operation with a slight loss of cell voltage@0.8 A cm-2 of 28 mV after 30 k cycles. The high performance can be ascribed to the high Pt area exposure, the enhanced Pt-Co coupling, and the prevented agglomeration in the mesoporous carbon wall. Overall, this strategy may contribute to the commercialization of fuel cells.

Tungsten Nitride with a Two-Dimensional Multilayer Structure for Boosting the Surface-Enhanced Raman Effect

The development of high-performance surface-enhanced Raman scattering (SERS) substrates is an urgent and important task. Here, tungsten nitride (WN) with a two-dimensional (2D) multilayer structure has been successfully prepared through a nitriding WO2.90 precursor. In addition to the highly active "hot spots" formed on the surface of the WN sheets, a large number of gaps between the nanosheets also exhibit a strong local surface plasmon resonance effect, which greatly improves the SERS activity. Evaluated as the SERS substrate, the WN with a 2D multilayer structure exhibits good SERS characteristics and good homogeneity and stability, even after strong acid, strong alkali, or long-term light treatment. Significantly, typical environmental contaminants such as dichlorophenol and butylated hydroxyanisole also exhibit strong Raman enhancement signals. This research provides a new method for designing inexpensive, high-activity, and universal SERS substrates.

Metalation of functionalized benzoquinoline-linked COFs for electrocatalytic oxygen reduction and lithium-sulfur batteries

It is worthwhile to explore and develop multifunctional composites with unique advantages for energy conversion and utilization. Post-synthetic modification (PSM) strategies can endow novel properties to already excellent covalent organic frameworks (COFs). In this study, we prepared a range of COF-based composites via a multi-step PSM strategy. COF-Ph-OH was acquired by demethylation between anhydrous BBr3 and - OMe, and then, M@COF-Ph-OH was further obtained by forming the N - M - O structure. COF-Ph-OH exhibited a 2e--dominated oxygen reduction reaction (ORR) pathway with high H2O2 selectivity, while M@COF-Ph-OH exhibited a 4e--dominated ORR pathway with low H2O2 selectivity, which was due to the introduction of a metal salt with a d electron structure that facilitated the acquisition of electrons and changed the adsorption energy of the reaction intermediate (*OOH). It was proven that the d electron structure was effective at regulating the reaction pathway of the electrocatalytic ORR. Moreover, Co@COF-Ph-OH showed better 4e- ORR properties than Fe@COF-Ph-OH and Ni@COF-Ph-OH. In addition, compared with the other sulfur-impregnated COF-based composites examined in this study, S-Co@COF-Ph-OH had a larger initial capacity, a weaker impedance, and a stronger cycling durability in Li-S batteries, which was attributed to the unique porous structure ensuring high sulfur utilization, the loaded cobalt accelerating LiPS electrostatic adsorption and promoting LiPS catalytic conversion, and the benzoquinoline ring structure being ultra-stable. This work offers not only a rational and feasible strategy for the synthesis of multifunctional COF-based composites, but also promotes their application in electrochemistry.

Promoting Effect of Nitride as Support for Pd Hydrodechlorination Catalyst

Pd-catalyzed reductive decontamination is considerably promising in the safe handling of various pollutants, and previous studies on heterogeneous Pd catalysts have demonstrated the key role of support in determining their catalysis performance. In this work, metal nitrides were studied as supports for Pd as a hydrodechlorination (HDC) catalyst. Density functional theory study showed that a transition metal nitride (TMN) support could effectively modulate the valence-band state of Pd. The upward shift of the d-band center reduced the energy barrier for water desorption from the Pd site to accommodate H₂/4-chlorophenol and increased the total energy released during HDC. The theoretical results were experimentally verified by synthesizing Pd catalysts onto different metal oxides and the corresponding nitrides. All studied TMNs, including TiN, Mo₂N, and CoN, showed satisfactorily stabilized Pd and render Pd with high dispersity. In line with theoretical prediction, TiN most effectively modulated the electronic states of the Pd sites and enhanced their HDC performance, with mass activity much higher than those of counterpart catalysts on other supports. The combined theoretical and experimental results shows that TMNs, especially TiN, are new and potentially important support for the highly efficient Pd HDC catalysts.

Advances in Low Pt Loading Membrane Electrode Assembly for Proton Exchange Membrane Fuel Cells

Hydrogen has the potential to be one of the solutions that can address environmental pollution and greenhouse emissions from traditional fossil fuels. However, high costs hinder its large-scale commercialization, particularly for enabling devices such as proton exchange membrane fuel cells (PEMFCs). The precious metal Pt is indispensable in boosting the oxygen reduction reaction (ORR) in cathode electrocatalysts from the most crucial component, i.e., the membrane electrode assembly (MEA). MEAs account for a considerable amount of the entire cost of PEMFCs. To address these bottlenecks, researchers either increase Pt utilization efficiency or produce MEAs with enhanced performance but less Pt. Only a few reviews that explain the approaches are available. This review summarizes advances in designing nanocatalysts and optimizing the catalyst layer structure to achieve low-Pt loading MEAs. Different strategies and their corresponding effectiveness, e.g., performance in half-cells or MEA, are summarized and compared. Finally, future directions are discussed and proposed, aiming at affordable, highly active, and durable PEMFCs.

Pt Single Atoms on CrN Nanoparticles Deliver Outstanding Activity and CO Tolerance in the Hydrogen Oxidation Reaction

The large-scale application of proton exchange membrane fuel cells is currently hampered by high cost of commercial Pt catalysts and their susceptibility to poisoning by CO impurities in H₂ feed. In this context, the development of CO-tolerant electrocatalysts with high Pt atom utilization efficiency for hydrogen oxidation reaction (HOR) is of critical importance. Herein, Pt single atoms are successfully immobilized on chromium nitride nanoparticles by atomic layer deposition method, denoted as Pt SACs/CrN. Electrochemical tests establish Pt SACs/CrN to be a very efficient HOR catalyst, with a mass activity that is 5.7 times higher than commercial PtRu/C. Strikingly, the excellent performance of Pt SACs/CrN is maintained after introducing 1000 ppm of CO in H₂ feed. The excellent CO-tolerance of Pt SACs/CrN is related to weaker CO adsorption on Pt single atoms. This work provides guidelines for the design and construction of active and CO-tolerant catalysts for HOR.

Bacterial nanocellulose as green support of platinum nanoparticles for effective methanol oxidation

Bacterial nanocellulose, BNC, has emerged as a new class of nanomaterials recognized as renewable, biodegradable, biocompatible and material for versatile applications. BNC also proved as a perfect support matrix for metallic nanoparticle synthesis and appeared as suitable alternative for widely used carbon based materials. Following the idea to replace commonly used carbon based materials for platinum supports with the green and sustainable one, BNC appeared as an excellent candidate. Herein, microwave assisted synthesis has been reported for the first time for platinum nanoparticles supported on BNC as green material. Bacterial nanocelullose-platinum catalyst, Pt/BNC, was investigated by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), atomic force microscopy (AFM), X-ray diffractometry (XRD) and transmission-electron microscopy (TEM) analysis. The obtained results confirmed successful synthesis of new Pt-based catalyst. It was found that Pt/BNC catalyst has high electrocatalytic performance in methanol oxidation reaction. Green/sustainable catalytic system is highly desirable and provided by the elegant microwave assisted synthesis of Pt/BNC will pave the way for a larger scale application and expedite the market penetration of such fuel cells.

Synergy of Platinum Single Atoms and Platinum Atomic Clusters on Sulfur-Doped Titanium Nitride Nanotubes for Enhanced Hydrogen Evolution Reaction

Highly dispersed Pt, such as Pt single atoms and atomic clusters, has great potential in the electrocatalytic hydrogen evolution reaction (HER) due to the high atomic efficiency and unique electronic configuration. Rationally regrating the electronic structure of Pt catalysts is desirable for promoting the HER performance. Herein, a 3D self-supported monolithic electrode consisting of Pt single atoms (Pt_SAs ) and Pt atomic clusters (Pt_ACs ) anchored on sulfur-doped titanium nitride nanotubes (S-TiN NTs) encapsulated in polyaniline (PANI) on Ti mesh (PANI@Pt/S-TiN NTs/Ti) via a facile electrochemical strategy for efficient HER is designed and synthesized. Contributed by the unique structure and composition and the synergy of Pt_SAs , Pt_ACs and S-TiN NTs, the PANI@Pt/S-TiN NTs/Ti electrode exhibits ultrahigh HER activities with only 12, 25 and 39 mV overpotentials at -10 mA cm^-2 in acidic, alkaline and neutral media, respectively, and can maintain a stable performance for 25 h. Impressively, the mass activities are respectively up to 26.1, 22.4, and 17.7 times as that of Pt/C/CC electrode. Theoretical calculation results show that the synergistic effect of Pt_SAs , Pt_ACs , and S-TiN NTs can optimize the electronic structure of Pt and generate multiple active sites with a thermodynamically favorable hydrogen adsorption free energy (ΔG_H* ), thereby resulting in an enhanced HER activity.

Corrosion Chemistry of Electrocatalysts

Electrocatalysts are the core components of many sustainable energy conversion technologies that are considered the most potential solution to the worldwide energy and environmental crises. The reliability of structure and composition pledges that electrocatalysts can achieve predictable and stable performance. However, during the electrochemical reaction, electrocatalysts are influenced directly by the applied potential, the electrolyte, and the adsorption/desorption of reactive species, triggering structural and compositional corrosion, which directly affects the catalytic behaviors of electrocatalysts (performance degradation or enhancement) and invalidates the established structure-activity relationship. Therefore, it is necessary to elucidate the corrosion behavior and mechanism of electrocatalysts to formulate targeted corrosion-resistant strategies or use corrosion reconstruction synthesis techniques to guide the preparation of efficient and stable electrocatalysts. Herein, the most recent developments in electrocatalyst corrosion chemistry are outlined, including corrosion mechanisms, mitigation strategies, and corrosion syntheses/reconstructions based on typical materials and important electrocatalytic reactions. Finally, potential opportunities and challenges are also proposed to foresee the possible development in this field. It is believed that this contribution will raise more awareness regarding nanomaterial corrosion chemistry in energy technologies and beyond.

Pt-Based Oxygen Reduction Reaction Catalysts in Proton Exchange Membrane Fuel Cells: Controllable Preparation and Structural Design of Catalytic Layer

Proton exchange membrane fuel cells (PEMFCs) have attracted extensive attention because of their high efficiency, environmental friendliness, and lack of noise pollution. However, PEMFCs still face many difficulties in practical application, such as insufficient power density, high cost, and poor durability. The main reason for these difficulties is the slow oxygen reduction reaction (ORR) on the cathode due to the insufficient stability and catalytic activity of the catalyst. Therefore, it is very important to develop advanced platinum (Pt)-based catalysts to realize low Pt loads and long-term operation of membrane electrode assembly (MEA) modules to improve the performance of PEMFC. At present, the research on PEMFC has mainly been focused on two areas: Pt-based catalysts and the structural design of catalytic layers. This review focused on the latest research progress of the controllable preparation of Pt-based ORR catalysts and structural design of catalytic layers in PEMFC. Firstly, the design principle of advanced Pt-based catalysts was introduced. Secondly, the controllable preparation of catalyst structure, morphology, composition and support, and their influence on catalytic activity of ORR and overall performance of PEMFC, were discussed. Thirdly, the effects of optimizing the structure of the catalytic layer (CL) on the performance of MEA were analyzed. Finally, the challenges and prospects of Pt-based catalysts and catalytic layer design were discussed.

Advances in platinum-based and platinum-free oxygen reduction reaction catalysts for cathodes in direct methanol fuel cells

Direct methanol fuel cells (DMFCs) have been the focus of future research because of their simple structure, abundant fuel sources, high energy conversion efficiency and low cost. Among the components in DMFC, the activity and stability of the cathode catalyst is the key to the performance and lifetime of the DMFCs. Oxygen reduction reaction (ORR) is an important electrode reaction on DMFC cathode. It is known that Pt is widely used in the fabrication of ORR catalysts, but the limited earth storage of Pt and its high price limit the use of Pt-based commercial catalysts in DMFCs. To overcome these problems, advances have been made on new low Pt-based catalysts and Pt-free catalysts in recent years. In this article, the development of novel ORR catalysts and the carbon supports is reviewed and discussed.

Regulating the scaling relationship for high catalytic kinetics and selectivity of the oxygen reduction reaction

The electrochemical oxygen reduction reaction (ORR) is at the heart of modern sustainable energy technologies. However, the linear scaling relationship of this multistep reaction now becomes the bottleneck for accelerating kinetics. Herein, we propose a strategy of using intermetallic-distance-regulated atomic-scale bimetal assembly (ABA) that can catalyse direct O‒O radical breakage without the formation of redundant *OOH intermediates, which could regulate the inherent linear scaling relationship and cause the ORR on ABA to follow a fast-kinetic dual-sites mechanism. Using in situ synchrotron spectroscopy, we directly observe that a self-adjustable N-bridged Pt = N₂ = Fe assembly promotes the generation of a key intermediate state (Pt‒O‒O‒Fe) during the ORR process, resulting in high reaction kinetics and selectivity. The well-designed Pt = N₂ = Fe ABA catalyst achieves a nearly two orders of magnitude enhanced kinetic current density at the half-wave potential of 0.95 V relative to commercial Pt/C and an almost 99% efficiency of 4-electron pathway selectivity, making it one of the potential ORR catalysts for application to the energy device of zinc‒air cells. This study provides a helpful design principle for developing and optimizing other efficient ORR electrocatalysts.

Improving kinetics for electrochemical oxygen reduction reaction is relevant to important sustainable energy technologies. The authors propose an atomic-scale bimetal assembly consisting Pt and Fe dual sites to regulate the inherent scaling relationship between intermediates for fast kinetics.

Alloying at a Subnanoscale Maximizes the Synergistic Effect on the Electrocatalytic Hydrogen Evolution

Bonding dissimilar elements to provide synergistic effects is an effective way to improve the performance of metal catalysts. However, as the properties become more dissimilar, achieving synergistic effects effectively becomes more difficult due to phase separation. Here we describe a comprehensive study on how subnanoscale alloying is always effective for inter-elemental synergy. Thirty-six combinations of both bimetallic subnanoparticles (SNPs) and nanoparticles (NPs) were studied systematically using atomic-resolution imaging and catalyst benchmarking based on the hydrogen evolution reaction (HER). Results revealed that SNPs always produce greater synergistic effects than NPs, the greatest synergistic effect was found for the combination of Pt and Zr. The atomic-scale miscibility and the associated modulation of electronic states at the subnanoscale were much different from those at the nanoscale, which was observed by annular-dark-field scanning transmission electron microscopy (ADF-STEM) and X-ray photoelectron spectroscopy (XPS), respectively.

Vanadium Nitride Supported on N-Doped Carbon as High-Performance ORR Catalysts for Zn–Air Batteries

It is desirable to prepare low-cost non-noble metal catalysts using a simple and efficient method. Herein, we display for the first time that nitrogen-doped hierarchical porous carbon-supported vanadium nitride (VN/NC/C-x) catalysts can be regulated by dicyandiamide (DCDA). The introduction of DCDA not only effectively controls the pore structure, but also plays an important role in adjusting oxygen vacancies and d-electrons. In addition, DCDA is not only a significant raw material for the N-doped carbon, but also a nitrogen source for the preparation of vanadium nitride. The VN/NC/C-3 catalyst was prepared after optimization of the preparation parameters, and the macro/micro structure demonstrates a superior ORR performance in alkaline media with a positive onset potential of 0.85 V and a half-wave potential of 0.75 V, the limiting current density is as high as 4.52 mA·cm−2, and the Tafel slope is only 75.54 mV·dec−1. The VN/NC/C-3-based Zn–air battery exhibits a highest peak power density (161.82 mW∙cm−2) and an excellent energy density (702.28 mAh·kgZn−1 and 861.51 Wh·kgZn−1). This work provides a valuable synthetic approach for the preparation of other transition metal nitride catalysts with a relative economic value and high performance.

Corrosion-Engineered Morphology and Crystal Structure Regulation toward Fe-Based Efficient Oxygen Evolution Electrodes

The rational regulation of catalysts with a well-controlled morphology and crystal structure has been demonstrated effective for optimizing the electrochemical performance. Herein, corrosion engineering was employed for the straightforward preparation of FeAl layered double hydroxide (LDH) nanosheets and Fe₃O₄ nanooctahedrons via the feasible modification of dealloying conditions. The FeAl-LDH nanosheets display an excellent catalytic performance for oxygen evolution reactions in 1 M KOH solution, such as low overpotentials (333 mV on glass carbon electrode and 284 mV on Ni foam at 10 mA cm⁻²), a small Tafel slope (36 mV dec⁻¹), and excellent durability (24 h endurance without deactivation). The distinguished catalytic features of the FeAl-LDH nanosheets comes from the Al and Fe synergies, oxygen vacancies, and well-defined two-dimensional (2D) layered LDH structure.

Effect of Precursor Status on the Transition from Complex to Carbon Shell in a Platinum Core-Carbon Shell Catalyst

Encapsulating platinum nanoparticles with a carbon shell can increase the stability of core platinum nanoparticles by preventing their dissolution and agglomeration. In this study, the synthesis mechanism of a platinum core-carbon shell catalyst via thermal reduction of a platinum-aniline complex was investigated to determine how the carbon shell forms and identify the key factor determining the properties of the Pt core-carbon shell catalyst. Three catalysts originating from the complexes with different platinum to carbon precursor ratios were synthesized through pyrolysis. Their structural characteristics were examined using various analysis techniques, and their electrochemical activity and stability were evaluated through half-cell and unit-cell tests. The relationship between the nitrogen to platinum ratio and structural characteristics was revealed, and the effects on the electrochemical activity and stability were discussed. The ratio of the carbon precursor to platinum was the decisive factor determining the properties of the platinum core-carbon shell catalyst.

Electronic Modulation of Pt Nanoparticles on Ni3N-Mo2C by Support-Induced Strategy for Accelerating Hydrogen Oxidation and Evolution

Electrochemical energy conversion and storage through hydrogen has revolutionized sustainable energy systems using fuel cells and electrolyzers. Regrettably, the sluggish alkaline hydrogen oxidation reaction (HOR) hampers advances in fuel cells. Herein, we report a Pt/Ni₃N-Mo₂C bifunctional electrocatalyst toward HOR and hydrogen evolution reaction (HER). The Pt/Ni₃N-Mo₂C exhibits remarkable HOR/HER performance in alkaline media. The mass activity at 50 mV and exchange current density of HOR are 5.1 and 1.5 times that of commercial Pt/C, respectively. Moreover, it possesses an impressive HER activity with an overpotential of 11 mV @ 10 mA cm^-2, which is lower than that of Pt/C and most reported electrocatalysts under the same conditions. Density functional theory (DFT) calculations combined with experimental results reveal that Pt/Ni₃N-Mo₂C not only possesses an optimal balance between hydrogen binding energy (HBE) and OH^- adsorption but also facilitates water adsorption and dissociation on the catalyst surface, which contribute to the excellent HOR/HER performance. Thus, this work may guide bifunctional HOR/HER catalyst design in the conversion and transport of energy.

Electrocatalysis in Alkaline Media and Alkaline Membrane-Based Energy Technologies

Hydrogen energy-based electrochemical energy conversion technologies offer the promise of enabling a transition of the global energy landscape from fossil fuels to renewable energy. Here, we present a comprehensive review of the fundamentals of electrocatalysis in alkaline media and applications in alkaline-based energy technologies, particularly alkaline fuel cells and water electrolyzers. Anion exchange (alkaline) membrane fuel cells (AEMFCs) enable the use of nonprecious electrocatalysts for the sluggish oxygen reduction reaction (ORR), relative to proton exchange membrane fuel cells (PEMFCs), which require Pt-based electrocatalysts. However, the hydrogen oxidation reaction (HOR) kinetics is significantly slower in alkaline media than in acidic media. Understanding these phenomena requires applying theoretical and experimental methods to unravel molecular-level thermodynamics and kinetics of hydrogen and oxygen electrocatalysis and, particularly, the proton-coupled electron transfer (PCET) process that takes place in a proton-deficient alkaline media. Extensive electrochemical and spectroscopic studies, on single-crystal Pt and metal oxides, have contributed to the development of activity descriptors, as well as the identification of the nature of active sites, and the rate-determining steps of the HOR and ORR. Among these, the structure and reactivity of interfacial water serve as key potential and pH-dependent kinetic factors that are helping elucidate the origins of the HOR and ORR activity differences in acids and bases. Additionally, deliberately modulating and controlling catalyst-support interactions have provided valuable insights for enhancing catalyst accessibility and durability during operation. The design and synthesis of highly conductive and durable alkaline membranes/ionomers have enabled AEMFCs to reach initial performance metrics equal to or higher than those of PEMFCs. We emphasize the importance of using membrane electrode assemblies (MEAs) to integrate the often separately pursued/optimized electrocatalyst/support and membranes/ionomer components. Operando/in situ methods, at multiscales, and ab initio simulations provide a mechanistic understanding of electron, ion, and mass transport at catalyst/ionomer/membrane interfaces and the necessary guidance to achieve fuel cell operation in air over thousands of hours. We hope that this Review will serve as a roadmap for advancing the scientific understanding of the fundamental factors governing electrochemical energy conversion in alkaline media with the ultimate goal of achieving ultralow Pt or precious-metal-free high-performance and durable alkaline fuel cells and related technologies.

A TiN@C core–shell support for improving Pt catalyst corrosion resistance

TiN@C composite support with high corrosion resistance improves catalyst durability because of SMSI between the Pt and N site in TiN.

Precisely controlled synthesis of Co/N species containing porous carbon for oxygen reduction reaction via anion exchange and CO2 activation

The synthesis strategy of highly dispersed Co/N-doped porous carbon materials using anion exchange resin and ionic liquids.