Synthesis of CeOx‐Decorated Pd/C Catalysts by Controlled Surface Reactions for Hydrogen Oxidation in Anion Exchange Membrane Fuel Cells

Due to the sluggish kinetics of the hydrogen oxidation reaction (HOR) in alkaline electrolytes, the development of more efficient HOR catalysts is essential for the next generation of anion‐exchange membrane fuel cells (AEMFCs). In this work, CeO_x is selectively deposited onto carbon‐supported Pd nanoparticles by controlled surface reactions, aiming to enhance the homogenous distribution of CeO_x and its preferential attachment to Pd nanoparticles, to achieve highly active CeO_x‐Pd/C catalysts. The catalysts are characterized by inductively coupled plasma–atomic emission spectroscopy, X‐ray diffraction, high‐resolution transmission electron microscopy, scanning transmission electron microscopy (STEM), electron energy loss spectroscopy, and X‐ray photoelectron spectroscopy to confirm the bulk composition, phases present, morphology, elemental mapping, local oxidation, and surface chemical states, respectively. The intimate contact between Pd and CeO_x is shown through high‐resolution STEM maps. The oxophilic nature of CeO_x and its effect on Pd are probed by CO stripping. The interfacial contact area between CeO_x and Pd nanoparticles is calculated for the first time and correlated to the electrochemical performance of the CeO_x‐Pd/C catalysts. Highest recorded HOR specific exchange current (51.5 mA mg^?1_Pd) and H₂–O₂ AEMFC performance (peak power density of 1,169 mW cm^?2 mg_Pd^?1) are obtained with a CeO_x‐Pd/C catalyst with Ce_0.38/Pd bulk atomic ratio.     

One‐Pot Synthesis of Framework Porphyrin Materials and Their Applications in Bifunctional Oxygen Electrocatalysis

Organic framework materials constructed by covalently linking organic building blocks into framework structures are highly regarded as paragons to precisely control the material structure at the atomic level. Herein, a direct synthesis methodology is proposed as a guidance for the bulk synthesis of organic framework materials. Framework porphyrin (POF) materials are one‐pot synthesized to demonstrate the advances of the direct synthesis methodology. The as‐synthesized POF materials are intrinsically 2D and exhibit impressive versatility in composition, structure, morphology, and function, delivering a free‐standing POF film, hybrids of POF and nanocarbon, and cobalt‐coordinated POF. When applied as electrocatalysts for oxygen reduction reaction and oxygen evolution reaction, the cobalt‐coordinated POF exhibits excellent bifunctional electrocatalytic performances comparable with noble‐metal‐based electrocatalysts. The direct synthesis methodology and resultant POF materials demonstrate the ability of controlling materials at the atomic level for energy electrocatalysis.     

Searching General Sufficient‐and‐Necessary Conditions for Ultrafast Hydrogen‐Evolving Electrocatalysis

The development of cost‐effective and high‐performance electrocatalysts for the hydrogen evolution reaction (HER) is one critical step toward successful transition into a sustainable green energy era. Different from previous design strategies based on single parameter, here the necessary and sufficient conditions are proposed to develop bulk non‐noble metal oxides which are generally considered inactive toward HER in alkaline solutions: i) multiple active sites for different reaction intermediates and ii) a short reaction path created by ordered distribution and appropriate numbers of these active sites. Computational studies predict that a synergistic interplay between the ordered oxygen vacancies (at pyramidal high‐spin Co³⁺ sites) and the O 2p ligand holes (OLH; at metallic octahedral intermediate‐spin Co⁴⁺ sites) in RBaCo₂O_5.5+δ (δ = 1/4; R = lanthanides) can produce a near‐ideal HER reaction path to adsorb H₂O and release H₂, respectively. Experimentally, the as‐synthesized (Gd_0.5La_0.5)BaCo₂O_5.75 outperforms the state‐of‐the‐art Pt/C catalyst in many aspects. The proof‐of‐concept results reveal that the simultaneous possession of ordered oxygen vacancies and an appropriate number of OLH can realize a near‐optimal synergistic catalytic effect, which is pivotal for rational design of oxygen‐containing materials.     

Ru Species Supported on MOF‐Derived N‐Doped TiO2/C Hybrids as Efficient Electrocatalytic/Photocatalytic Hydrogen Evolution Reaction Catalysts

The development of efficient catalysts is of great importance for hydrogen evolution reaction (HER) of water splitting via electrocatalytic/photocatalytic processes to remediate the current severe environmental and energy problems. By aid of the stabilization effects of uncoordinated groups and inherent pore‐confinement of amine‐functionalized metal–organic frameworks (NH₂‐MIL‐125), two forms of Ru species including nanoparticles (NPs) and/or single atoms (SAs) can be firmly embedded in NH₂‐MIL‐125 derived N‐doped TiO₂/C support (N‐TC), and thus obtain two kinds of samples named Ru‐NPs/SAs@N‐TC and Ru‐SAs@N‐TC, respectively. In the synthetic process, the initial feeding amount of Ru³⁺ ions not only strongly determines the final size and dispersion states of Ru species but also the morphology and defective structures of N‐TC support. Impressively, Ru‐NPs/SAs@N‐TC exhibit superior catalytic activities to Ru‐SAs@N‐TC for either electrocatalytic or photocatalytic HER. This should be attributed to its larger specific surface area and benefiting from synergistic coupling of Ru NPs and Ru SAs. It is envisioned that the present work can provide a new avenue for development of high‐efficiency and multifunctional hybrid catalysts in sustainable energy conversion.     

A Cake‐Style CoS2@MoS2/RGO Hybrid Catalyst for Efficient Hydrogen Evolution

A three‐tiered cake‐style composite is elaborately established, with the characteristic of a double‐deck of MoS₂ nanosheets and reduction of graphene oxide (RGO) sheets dotted with CoS₂ nanoparticles (CoS₂@MoS₂/RGO). Because of the prominent synergistic effect of graphene acting as conductive support, MoS₂ and CoS₂ providing abundant catalytically active sites, and the cake‐style structure promoting mechanical stability, the CoS₂@MoS₂/RGO exhibits a superior hydrogen evolution reaction activity with a small overpotential of 98 mV at cathodic current density of 10 mA cm^?2, and a small Tafel slope of 37.4 mV dec^?1, as well as excellent cycling stability. Density functional theory calculations reveal that the hydrogen adsorption free energy of CoS₂@MoS₂/RGO is close to zero.     

Regulating the Electronic Structure of CoP Nanosheets by O Incorporation for High‐Efficiency Electrochemical Overall Water Splitting

The exploration of earth‐abundant and high‐efficiency bifunctional electrocatalysts for overall water splitting is of vital importance for the future of the hydrogen economy. Regulation of electronic structure through heteroatom doping represents one of the most powerful strategies to boost the electrocatalytic performance of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, a rational design of O‐incorporated CoP (denoted as O‐CoP) nanosheets, which synergistically integrate the favorable thermodynamics through modification of electronic structures with accelerated kinetics through nanostructuring, is reported. Experimental results and density functional theory simulations manifest that the appropriate O incorporation into CoP can dramatically modulate the electronic structure of CoP and alter the adsorption free energies of reaction intermediates, thus promoting the HER and OER activities. Specifically, the optimized O‐CoP nanosheets exhibit efficient bifunctional performance in alkaline electrolyte, requiring overpotentials of 98 and 310 mV to deliver a current density of 10 mA cm^?2 for HER and OER, respectively. When served as bifunctional electrocatalysts for overall water splitting, a low cell voltage of 1.60 V is needed for achieving a current density of 10 mA cm^?2. This proposed anion‐doping strategy will bring new inspiration to boost the electrocatalytic performance of transition metal–based electrocatalysts for energy conversion applications.     

Covalent 0D–2D Heterostructuring of Co9S8–MoS2 for Enhanced Hydrogen Evolution in All pH Electrolytes

Ultrasmall Co₉S₈ nanoparticles are introduced on the basal plane of MoS₂ to fabricate a covalent 0D–2D heterostructure that enhances the hydrogen evolution reaction (HER) activity of electrochemical water splitting. In the heterostructure, separate phases of Co₉S₈ and MoS₂ are formed, but they are connected by Co–S–Mo type covalent bonds. The charge redistribution from Co to Mo occurring at the interface enhances the electron‐doped characteristics of MoS₂ to generate electron‐rich Mo atoms. Besides, reductive annealing during the synthesis forms S defects that activates adjacent Mo atoms for further enhanced HER activity as elucidated by the density functional theory (DFT) calculation. Eventually, the covalent Co₉S₈–MoS₂ heterostructure shows amplified HER activity as well as stability in all pH electrolytes. The synergistic effect is pronounced when the heterostructure is coupled with a porous Ni foam (NF) support to form Co₉S₈–MoS₂/NF that displays superior performance to those of the state‐of‐the‐art non‐noble metal electrocatalysts, and even outperforms a commercial Pt/C catalyst in a practically meaningful, high current density region in alkaline (>170 mA cm^?2) and neutral (>60 mA cm^?2) media. The high HER performance and stability of Co₉S₈–MoS₂ heterostructure make it a promising pH universal alternative to expensive Pt‐based electrocatalysts for practical water electrolyzers.     

One‐Step Self‐Assembly Fabrication of High Quality NixMg1‐xO Bowl‐Shaped Array Film and Its Enhanced Photocurrent by Mg,2+ Doping

A series of high quality Ni_xMg_1‐xO bowl‐shaped array films are successfully prepared by a simple one‐step assembly of polystyrene colloidal spheres and metal oxide precursors at oil–water interface, and further used to fabricate nanodevices. The doping of Mg²⁺ can greatly enhance the current and spectrum responsivity of NiO film‐based nanodevice. The maximum R_λ value of these bowl‐shaped Ni_xMg_1‐xO film‐based devices measured in the study shows 4–5 orders of enhancement than the previously reported Ni_xMg_1‐xO film at equal doping.     

One‐Step Synthesis of CoS‐Doped β‐Co(OH)2@Amorphous MoS2+x Hybrid Catalyst Grown on Nickel Foam for High‐Performance Electrochemical Overall Water Splitting

Developing efficient and economical electrocatalysts for hydrogen evolution reaction and oxygen evolution reaction with readily available metals is one of the main challenges for large scale hydrogen/oxygen production. This study reports one step synthesis of cobalt and molybdenum hybrid materials for high performance overall water splitting. The binder‐free CoS‐doped β‐Co(OH)₂@amorphous MoS_2+x is coated on nickel foam (NF) to form 3D networked nanoplates that have large surface area and high durability for electrochemical reactions. The catalytic activity of electrocatalyst for hydrogen evolution is mainly attributed to the unsaturated sulfur site of amorphous MoS_2+x. Meanwhile, the CoS‐doped β‐Co(OH)₂ plays the major role in oxygen evolution. CoS‐doped β‐Co(OH)₂ and aMoS_2+x are strongly bound to each other due to CoS_x bridging. This CoS? Co(OH)₂@aMoS_2+x/NF hybrid exhibits excellent catalytic activity and stability for overall water splitting. For over 100 000 s the cell voltage required to achieve the current density of 10 mA cm^–2 is only 1.58 V, which is remarkably low among the commercially available electrocatalysts. The findings open up an easy and inexpensive method of large scale fabrication of bifunctional electrocatalysts for overall water splitting.     

Activating Basal Planes and S‐Terminated Edges of MoS2 toward More Efficient Hydrogen Evolution

Molybdenum disulfide (MoS₂) has been considered as a promising alternative to platinum (Pt)‐based catalyst for hydrogen evolution reaction (HER) due to its low cost and high catalytic activity. However, stable 2H phase of MoS₂ (2H‐MoS₂) exhibits low catalytic activity in HER due to the inert basal plane and S‐edge. Thus, to exploit the basal plane and S‐edge for additional electrocatalytic activity, a facile strategy is developed to prepare P‐doped 2H‐MoS₂ film on conductive substrate via low‐temperature heat treatment. Due to the inherent difficulty of P‐doping into MoS₂ crystal structure, oxygen (O)‐doping is utilized to aid the P‐doping process, as supported by the first‐principles calculations. Interestingly, P‐doping could dramatically reduce Mo valence charge, which results in the functionalization of the inert MoS₂ basal plane and S‐edge. In agreement with simulation results, P‐doped 2H‐MoS₂ electrode exhibits enhanced catalytic performance in H₂ generation with low onset potential (130 mV) and small Tafel slope of 49 mV dec^?1. The enhanced catalytic performance arises from the synergistic effect of the activated basal plane, S‐edge, and Mo‐edge sites, leading to favorable hydrogen adsorption energies. Most importantly, improved cyclic stability is achieved, which reveals chemically inert properties of P‐doped 2H‐MoS₂ in acidic electrolyte.     

One‐Pot,Facile, and Versatile Synthesis of Monolayer MoS2/WS2 Quantum Dots as Bioimaging Probes and Efficient Electrocatalysts for Hydrogen Evolution Reaction

In this work, uniform molybdenum disulfide (MoS₂)/tungsten disulfide (WS₂) quantum dots are synthesized by the combination of sonication and solvothermal treatment of bulk MoS₂/WS₂ at a mild temperature. The resulting products possess monolayer thickness with an average size about 3 nm. The highly exfoliated and defect‐rich structure renders these quantum dots plentiful active sites for the catalysis of hydrogen evolution reaction (HER). The MoS₂ quantum dots exhibit a small HER overpotential of ≈120 mV and long‐term durability. Moreover, the strong fluorescence, good cell permeability, and low cytotoxicity make them promising and biocompatible probes for in vitro imaging. In addition, this work may provide an alternative facile approach to synthesize the quantum dots of transition metal dichalcogenides or other layered materials on a large scale.     

Template‐Assisted Synthesis of Metallic 1T′‐Sn0.3W0.7S2 Nanosheets for Hydrogen Evolution Reaction

Crystal phase control still remains a challenge for the precise synthesis of 2D layered metal dichalcogenide (LMD) materials. The T′ phase structure has profound influences on enhancing electrical conductivity, increasing active sites, and improving intrinsic catalytic activity, which are urgently needed for enhancing hydrogen evolution reaction (HER) activity. Theoretical calculations suggest that metastable T′ phase 2D Sn_1?xW_xS₂ alloys can be formed by combining W with 1T tin disulfide (SnS₂) as a template to achieve a semiconductor‐to‐metallic transition. Herein, 2D Sn_1?xW_xS₂ alloys with varying x are prepared by adjusting the molar ratio of reactants via hydrothermal synthesis, among which Sn_0.3W_0.7S₂ displays a maximum of concentration of 81% in the metallic phase and features a distorted octahedral‐coordinated metastable 1T′ phase structure. The obtained 1T′‐Sn_0.3W_0.7S₂ has high intrinsic electrical conductivity, lattice distortion, and defects, showing a prominently improved HER catalytic performance. Metallic Sn_0.3W_0.7S₂ coupled with carbon black exhibits at least a 215‐fold improvement compared to pristine SnS₂. It has excellent long‐term durability and HER activity. This work reveals a general phase transition strategy by using T phase materials as templates and merging heteroatoms to achieve synthetic metastable phase 2D LMDs that have a significantly improved HER catalytic performance.     

Boosting H2O2‐Guided Chemodynamic Therapy of Cancer by Enhancing Reaction Kinetics through Versatile Biomimetic Fenton Nanocatalysts and the Second Near‐Infrared Light Irradiation

Fenton reaction–based chemodynamic therapy (CDT) has attracted considerable attention for tumor treatment, because the Fenton reaction can degrade endogenous H₂O₂ within the tumor to form reactive oxygen species (ROS) to kill cancer cells. The kinetics of the Fenton reaction has significantly influenced its treatment efficacy. It is crucial to enhance the reaction kinetics at the maximum H₂O₂ concentration to quickly produce vast amounts of ROS to achieve treatment efficacy, which to date, has not been realized. Herein, reported is an efficacious CDT treatment of breast cancer using biomimetic CS‐GOD@CM nanocatalysts, which are rationally designed to significantly boost the Fenton reaction through improvement of H₂O₂ concentration within tumors, and application of the second near‐infrared (NIR‐II) light irradiation at the maximum concentration, which is monitored by photoacoustic imaging. The biomimetic nanocatalysts are composed of ultra‐small Cu_2?xSe (CS) nanoparticles, glucose oxidase (GOD), and tumor cell membrane (CM). The nanocatalysts can be retained in tumor for more than two days to oxidize glucose and produce an approximately 2.6‐fold increase in H₂O₂ to enhance the Fenton reaction under the NIR‐II irradiation. This work demonstrates for the first time the CDT treatment of cancer enhanced by the NIR‐II light.     

Synergistically Tuning Electronic Structure of Porous β‐Mo2C Spheres by Co Doping and Mo‐Vacancies Defect Engineering for Optimizing Hydrogen Evolution Reaction Activity

The development of novel non‐noble electrocatalysts with controlled structure and surface composition is critical for efficient electrochemical hydrogen evolution reaction (HER). Herein, the rational design of porous molybdenum carbide (β‐Mo₂C) spheres with different surface engineered structures (Co doping, Mo vacancies generation, and coexistence of Co doping and Mo vacancies) is performed to enhance the HER performance over the β‐Mo₂C‐based catalyst surface. Density functional theory calculations and experimental results reveal that the synergistic effect of Co doping with Mo vacancies increases the electron density around the Fermi‐level and modulates the d band center of β‐Mo₂C so that the strength of the Mo? H bond is reasonably optimized, thus leading to an enhanced HER kinetics. As expected, the optimized Co₅₀‐Mo₂C‐12 with porous structure displays a low overpotential (η₁₀ = 125 mV), low‐onset overpotential (η_onset = 27 mV), and high exchange current density (j₀ = 0.178 mA cm^?2). Furthermore, this strategy is also successfully extended to develop other effective metal (e.g., Fe and Ni) doped β‐Mo₂C electrocatalyst, indicating that it is a universal strategy for the rational design of highly efficient metal carbide‐based HER catalysts and beyond.     

One‐Pot Synthesis of Freestanding Porous Palladium Nanosheets as Highly Efficient Electrocatalysts for Formic Acid Oxidation

Freestanding ultrathin 2D noble metal nanosheets have drawn enormous attention due to their potential applications in various fields. However, the synthesis of 2D noble metal nanosheets still remains a great challenge due to the lack of an intrinsic driving force for anisotropic growth of 2D structures. Here, a facile one‐pot synthesis of ultrathin freestanding porous Pd nanosheets (≈2.5 µm in lateral size and 10 nm in thickness) flexibly knitted by interweaved ultrathin nanowires with the assistance of poly(diallyldimethylammonium chloride) is presented. Nanoparticles attachment and subsequent self‐assembly in the synthetic process are responsible for the formation of such intriguing nanostructures. Moreover, finely controlling the pH value of the precursor solution leads to yield different Pd nanostructures with tunable dimensionalities, including 3D nanoflowers, 2D nanosheets, and 1D nanochains. Owing to the unique structural features, the obtained freestanding porous Pd nanosheets exhibit excellent electrocatalytic activity and stability towards formic acid oxidation compared to those of other dimensional counterparts and commercial Pd black.     

A Composite of Carbon‐Wrapped Mo2C Nanoparticle and Carbon Nanotube Formed Directly on Ni Foam as a High‐Performance Binder‐Free Cathode for Li‐O2 Batteries

Cathode design is indispensable for building Li‐O₂ batteries with long cycle life. A composite of carbon‐wrapped Mo₂C nanoparticles and carbon nanotubes is prepared on Ni foam by direct hydrolysis and carbonization of a gel composed of ammonium heptamolybdate tetrahydrate and hydroquinone resin. The Mo₂C nanoparticles with well‐controlled particle size act as a highly active oxygen reduction reactions/oxygen evolution reactions (ORR/OER) catalyst. The carbon coating can prevent the aggregation of the Mo₂C nanoparticles. The even distribution of Mo₂C nanoparticles results in the homogenous formation of discharge products. The skeleton of porous carbon with carbon nanotubes protrudes from the composite, resulting in extra voids when applied as a cathode for Li‐O₂ batteries. The batteries deliver a high discharge capacity of ≈10 400 mAh g^?1 and a low average charge voltage of ≈4.0 V at 200 mA g^?1. With a cutoff capacity of 1000 mAh g^?1, the Li‐O₂ batteries exhibit excellent charge–discharge cycling stability for over 300 cycles. The average potential polarization of discharge/charge gaps is only ≈0.9 V, demonstrating the high ORR and OER activities of these Mo₂C nanoparticles. The excellent cycling stability and low potential polarization provide new insights into the design of highly reversible and efficient cathode materials for Li‐O₂ batteries.