Search

A unique metallic IrxPb network structure with high Ir atomic utilization and enhanced performance for oxygen evolution.

Cost-effective and highly efficient Fe–N–C single-atom catalysts (SACs) have been considered to be one of the most promising potential Pt substitutes for the cathodic oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). Nevertheless, they are subject to severe oxidative corrosion originating from the Fenton reaction, leading to poor long-time durability of PEMFCs. Herein, we propose a MnOx engineered Fe–N–C SAC (Mn–Fe–N–C SAC) to reduce and even eliminate the stability issue, as MnOx accelerates the degradation of the H2O2 by-product via a disproportionation reaction to weaken the Fenton reaction. As a result, the Mn–Fe–N–C SAC shows an ultralow H2O2 yield and a negligible half-wave potential shift after 10 000 continuous potential cycles, demonstrating excellent ORR stability. Besides, the Mn–Fe–N–C SAC also shows an improved ORR activity compared to the common Fe–N–C SAC. Results show that the MnOx interacts with the Fe–Nx site, possibly forming Fe–Mn or Fe–O–Mn bonds, and enhances the intrinsic activity of single iron sites. This work provides a method to overcome the stability problem of Fe–N–C SACs while still yielding excellent catalytic activity, thus showing great promise for application in PEMFCs.

We elucidate the structural evolution of CoN4 sites during thermal activation by developing a zeolitic imidazolate framework (ZIF)-8-derived carbon host as an ideal model for Co2+ ion adsorption. Subsequent in situ X-ray absorption spectroscopy analysis can dynamically track the conversion from inactive Co-OH and Co-O species into active CoN4 sites. The critical transition occurs at 700 °C and becomes optimal at 900 °C, generating the highest intrinsic activity and four-electron selectivity for the oxygen reduction reaction (ORR). DFT calculations elucidate that the ORR is kinetically favored by the thermal-induced compressive strain of Co-N bonds in CoN4 active sites formed at 900 °C. Further, we developed a two-step (i.e., Co ion doping and adsorption) Co-N-C catalyst with increased CoN4 site density and optimized porosity for mass transport, and demonstrated its outstanding fuel cell performance and durability.

Atomically dispersed and nitrogen coordinated single metal sites (M-N-C, M=Fe, Co, Ni, or Mn) are the popular platinum group-metal (PGM)-free catalysts for many electrochemical reactions. Traditional wet-chemistry catalyst synthesis often requires complex procedures with unsatisfied reproducibility and scalability. Here, we report a chemical vapor deposition (CVD) strategy to synthesize the promising single metal site (M-N-C) catalysts. The deposition of gaseous 2-methylimidazole onto ZnO substrates doped with M, followed by an in-situ thermal activation, was proved effective in generating single metal sites well dispersed into porous carbon. In particular, an optimal CVD-derived Fe-N-C catalyst is featured with atomically dispersed FeN4 sites with increased Fe loading relative to other catalysts from wet-chemistry synthesis. The catalyst exhibited outstanding oxygen-reduction activity in acidic electrolytes, which was further studied in proton-exchange membrane fuel cells with encouraging performance. The CVD synthesis sheds some light on the mass production of single metal site catalysts towards advanced electrocatalysis.

Alkaline anion exchange membrane (AEM) electrolysers to produce hydrogen from water are still at an early stage of development, and their performance is far lower than that of systems based on proton exchange membranes. Here, we report an ammonium-enriched anion exchange ionomer that improves the performance of an AEM electrolyser to levels approaching that of state-of-the-art proton exchange membrane electrolysers. Using rotating-disk electrode experiments, we show that a high pH (>13) in the electrode binder is the critical factor for improving the activity of the hydrogen- and oxygen-evolution reactions in AEM electrolysers. Based on this observation, we prepared and tested several quaternized polystyrene electrode binders in an AEM electrolyser. Using the binder with the highest ionic concentration and a NiFe oxygen evolution catalyst, we demonstrated performance of 2.7 A cm−2 at 1.8 V without a corrosive circulating alkaline solution. The limited durability of the AEM electrolyser remains a challenge to be addressed in the future. Anion exchange membrane water electrolysers have potential cost advantages over proton exchange membrane electrolysers, but their performance has lagged behind. Here the authors investigate the cause of the poor performance of anion exchange membrane electrolysers and design ionomers that can overcome some of the challenges.

Atomically dispersed Fe–N–C materials recently hold great interest in costly Pt substitution for the cathodic oxygen reduction reaction of fuel cells. However, the heat treatment involved in the ma...

Proton-exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) are promising power sources from portable electronic devices to vehicles. The high-cost issue of these low-temperature fuel cells can be primarily addressed by using platinum-group metal (PGM)-free oxygen reduction reaction (ORR) catalysts, in particular atomically dispersed metal–nitrogen–carbon (M–N–C, M = Fe, Co, Mn). Furthermore, a significant advantage of M–N–C catalysts is their superior methanol tolerance over Pt, which can mitigate the methanol cross-over effect and offer great potential of using a higher concentration of methanol in DMFCs. Here, we investigated the ORR catalytic properties of M–N–C catalysts in methanol-containing acidic electrolytes via experiments and density functional theory (DFT) calculations. FeN4 sites demonstrated the highest methanol tolerance ability when compared to metal-free pyridinic N, CoN4, and MnN4 active sites. The methanol adsorption on MN4 sites is even strengthened when electrode potentials are applied during the ORR. The negative influence of methanol adsorption becomes significant for methanol concentrations higher than 2.0 M. However, the methanol adsorption does not affect the 4e− ORR pathway or chemically destroy the FeN4 sites. The understanding of the methanol-induced ORR activity loss guides the design of promising M–N–C cathode catalyst in DMFCs. Accordingly, we developed a dual-metal site Fe/Co–N–C catalyst through a combined chemical-doping and adsorption strategy. Instead of generating a possible synergistic effect, the introduced Co atoms in the first doping step act as “scissors” for Zn removal in metal–organic frameworks (MOFs), which is crucial for modifying the porosity of the catalyst and providing more defects for stabilizing the active FeN4 sites generated in the second adsorption step. The Fe/Co–N–C catalyst significantly improved the ORR catalytic activity and delivered remarkably enhanced peak power densities (i.e., 502 and 135 mW cm−2) under H2–air and methanol–air conditions, respectively, representing the best performance for both types of fuel cells. Notably, the fundamental understanding of methanol tolerance, along with the encouraging DMFC performance, will open an avenue for the potential application of atomically dispersed M–N–C catalysts in other direct alcohol or ammonia fuel cells.

The urgent need to address the high-cost issue of proton-exchange membrane fuel cell (PEMFC) technologies, particularly for transportation applications, drives the development of simultaneously highly active and durable platinum group metal-free (PGM-free) catalysts and electrodes. The past decade has witnessed remarkable progress in exploring PGM-free cathode catalysts for the oxygen reduction reaction (ORR) to overcome sluggish kinetics and catalyst instability in acids. Among others, scientists have identified the newly emerging atomically dispersed transition metal (M: Fe, Co, or/and Mn) and nitrogen co-doped carbon (M-N-C) catalysts as the most promising alternative to PGM catalysts. Here, we provide a comprehensive review of significant breakthroughs, remaining challenges, and perspectives regarding the M-N-C catalysts in terms of catalyst activity, stability, and membrane electrode assembly (MEA) performance. A variety of novel synthetic strategies demonstrated effectiveness in improving intrinsic activity, increasing active site density, and attaining optimal porous structures of catalysts. Rationally designing and engineering the coordination environment of single metal MNx sites and their local structures are crucial for enhancing intrinsic activity. Increasing the site density relies on the innovative strategies of restricting the migration and agglomeration of single metal sites into metallic clusters. Relevant understandings provide the correlations among the nature of active sites, nanostructures, and catalytic activity of M-N-C catalysts at the atomic scale through a combination of experimentation and theory. Current knowledge of the transferring catalytic properties of M-N-C catalysts to MEA performance is limited. Rationally designing morphologic features of M-N-C catalysts play a vital role in boosting electrode performance through exposing more accessible active sites, realizing uniform ionomer distribution, and facilitating mass/proton transports. We outline future research directions concerning the comprehensive evaluation of M-N-C catalysts in MEAs. The most considerable challenge of current M-N-C catalysts is the unsatisfied stability and rapid performance degradation in MEAs. Therefore, we further discuss practical methods and strategies to mitigate catalyst and electrode degradation, which is fundamentally essential to make M-N-C catalysts viable in PEMFC technologies.

Increased use of pesticides in agriculture requires new advanced techniques to monitor both environmental levels and human exposure of pesticides to avoid potential adverse health outcomes in sensitive populations. Atrazine is widely used to control broadleaf weeds, and here we developed a new sensor capable of detecting diaminochlorotriazine (DACT), the major metabolite and biomarker of atrazine exposure. We established an Au@PtPd nanoparticles labeled lateral flow immunoassay (LFIA) for immunochromatographic based rapid detection of urinary DACT. The detection was based on competitive immunoassay between the analyte and the BSA-conjugated antigen. As evaluated, the coupled mesoporous core-shell Au@PtPd nanoparticles, with superior peroxidase-like activity, as the signal indicator offers a rapid direct chromatographic readout inversely correlated with the concentration of analytes, providing a detection limit of 0.7 ng/mL for DACT. Moreover, the detection limits were boosted to as low as 11 pg/mL with the detectable range from 10 pg/ml to 10 ng/mL, through a one-step catalytic chromogenic reaction. A rapid readout device was developed by 3D printing to provide a stable real-time quantification of the color intensity capable of assessing both chromatographic and absorbance results. This Au@PtPd nanoparticle-based immunosensing platform, as well as the 3D printed readout device, provide a promising tool for on-site and ultrasensitive detection of pesticide biomarkers.

The Fe–N–C material is a promising non-noble-metal electrocatalyst for oxygen reduction reaction (ORR). Further improvement on the ORR activity is highly desired in order to replace Pt/C in acidic media. Herein, we developed a new-type of single-atom Fe–N–C electrocatalyst, in which Fe–N x active sites were modified by P atoms. The half-wave potential of the optimized material reached 0.858 V, which is 23 mV higher than that of the pristine one in a 0.1 mol L−1 HClO4 solution. Density functional theory (DFT) calculations revealed that P-doping can reduce the thermodynamic overpotential of the rate determining step and consequently improve the ORR activity.

Atomically dispersed and nitrogen-coordinated single iron sites (FeN4) embedded in carbon (Fe-N-C) catalysts are the most promising platinum group metal (PGM)-free catalysts. However, they have yet to match their Pt counterparts for oxygen reduction reaction (ORR) activity and stability in proton exchange membrane fuel cells (PEMFCs). Here, we developed viable Fe-N-C catalysts, which, for the first time, demonstrated competitive activity to that of Pt/C catalysts and dramatically enhanced stability and durability under practical PEMFC operating conditions. The most active Fe-N-C catalyst achieved a record half-wave potential (E1/2 = 0.915 V vs. RHE at 0.6 mgcatcm-2) and an ORR mass activity of 10.5 mA mgcat at 0.9 V in (RDE) tests, exceeding a Pt/C baseline catalyst (60 µgPt cm-2) by 40 mV in acidic electrolytes. This compelling activity of the Fe-N-C catalyst in aqueous acids on rotating disk electrode (RDE) was successfully transferred to a fuel cell membrane electrode assemblies (MEAs), generating an initial current density of 44.2 mA cm-2 exceeding the U.S. DOE 2025 target (i.e., 44 mA cm-2) at 0.9 VIR-free under O2. Under practical hydrogen-air conditions, record 151 mA cm-2 at 0.8 V and peak power density of 601 mW cm-2 were achieved. Importantly, we discovered that depositing nitrogen-carbon species on the catalyst surface via chemical vapor deposition (CVD) dramatically enhanced catalyst stability, evidenced by performance durability after accelerated stress tests (30 000 square-wave voltage cycles under H2/air) and long-term steady-state life tests (> 300 hours at 0.67 V). Innovative identical location-scanning transmission electron microscopy (IL-STEM) experiments confirmed that the CVD process leads to deposition of nitrogen-doped carbon onto the catalyst surfaces. Along with theoretical modeling, a reconstruction of the carbon structure adjacent to FeN4 sites leads to increased robustness against demetallation and carbon oxidation. This work opens new avenues for developing earth-abundant iron-based catalysts with extraordinary activity and stability, thus competing with Pt and addressing the cost barrier of current PEMFCs.

The electrochemical production of hydrogen peroxide is enjoying increasing attention by endowing a promising alternative to the traditional complex and energy-intensive anthraquinone process. Engin...

Here, a label-free fluorescent sensor was developed for detection Fe (III) by utilizing the quenching effect of Fe (III) on the fluorescence of the hydroxyl functionalized metal-organic framework MIL-53(Fe)-(OH)2, which was synthesized by using a one-step solvothermal method. The specific binding interaction between Fe (III) and hydroxyl facilitated the absorption of free Fe (III) to MIL-53(Fe)-(OH)2, which leads to rapid fluorescent intensity quenching effect. The potential quenching mechanism was proved to be the photo-induced electron transfer (PET) from electron-rich ligands of MIL-53(Fe)-(OH)2 to the half-filled 3d orbitals of free Fe (III) in the sample solution. For in-field applications, the fluorescence signal was detected rapidly by using a homemade 3D-printed, portable, and low-cost smartphone sensor. A commercial 365 nm UV LED light was adopted as the excitation light source, while the camera in a smartphone was utilized as the optical detector. The fluorescent signals obtained by using the smartphone sensor were in a good agreement with those obtained from a commercial microplate reader. Under the optimal assay conditions, the linear detection range of Fe (III) was 5.0–200 μM, and the limit of detection is 1.7 μM. This result is compatible with the commercial microplate reader. The developed method was successfully adopted to detect Fe (III) in human serum and environmental water samples with acceptable recovery values of 90–108.5%. The portable, low-cost, fast-response, user-friendly and sensitive fluorescent protocol based on a self-quenching fluorescent nanoprobe can be conducted at home or anywhere else without sophisticated instruments, showing a great application potential in clinical diagnosis, on-site environmental monitoring and healthcare at home.

Recently, electrocatalysts based on anchored dispersive/isolated single metal atoms on conductive carbon supports have demonstrated great promise to substitute costly Pt for the oxygen reduction reaction (ORR) in the field of fuel cells or metal-air batteries. However, developments of cost-efficient single-atom Fe catalysts with high activities are still facing various hardships. Here, we developed a facile way to synthesize isolated iron atoms anchored on the carbon nanotube (CNT) involving a one-pot pyrrole polymerization on a self-degraded organic template and a subsequent pyrolysis. The as-obtained electrocatalyst possessed unique characteristics of abundant nanopores in the wall of conductive CNTs to host the abundant atomic Fe-Nx active sites, showing ultrahigh ORR activity (half-wave potential: 0.93 V, kinetic current density: 59.8 mA/cm2 at 0.8 V), better than that of commercial Pt/C (half-wave potential: 0.91 V; kinetic current density: 38.0 mA/cm2 at 0.8 V) in an alkaline electrolyte. Furthermore, good ORR activity has been proven in acidic solution with a half-wave-potential of 0.73 V.

The development of efficient Fe–N–C materials enriched with single-atom Fe sites toward the oxygen reduction reaction (ORR) is still a great challenge because Fe atoms are mobile and easily aggrega...

A simple and rapid process of ReO4– (as a surrogate of TcO4–) removal from aqueous solutions based on the electrically switched ion exchange (ESIX) method has been demonstrated in this work. Activa...

Engineering highly efficient and cost-effective catalysts for the electrochemical oxygen evolution reaction (OER) is crucial for accelerating the development of renewable energy techniques due to the pivotal role of OER in rechargeable metal–air batteries and water electrolyzers. Recently, porous nonprecious metal catalysts (PNMCs) have received tremendous interest for application in the OER. Metal–organic frameworks (MOFs) built from metal ions and organic linkers have been demonstrated to be promising precursors for preparing PNMCs for the OER owing to their tunable structures/compositions, high surface area and large pore volume. Benefitting from the versatility of compositional/structural modification, MOFs and MOFs-derived PNMCs are robust in generating various high density active sites, which greatly contribute to their electrochemical OER performances. In this review, we first summarize the composition engineering of pristine MOFs and their derivatives, such as heteroatom-doped carbon, metal oxides/phosphides/sulfides/selenides and their hybrids, followed by structural/morphology engineering, including nano-coating and nano-perforating, and the configuration of high-dimensional architecture and single atom sites. Simultaneously, insights toward an in-depth understanding of the actual active sites and the intrinsic mechanism for OER enhancement are highlighted combined with experimental and theoretical studies. Finally, the challenges and perspectives for engineering MOF-based electrocatalysts are addressed.

Recently, cobalt-based polar materials with an unique catalytic behavior have been discovered and have shown promising electrochemical performance in lithium−sulfur (Li−S) batteries. However, there is lack of consensus on the relationship between catalytic activity and composition of different polar materials. Inconsistencies in morphologies, chemical compositions, and testing conditions lead to disparate results from laboratory to laboratory. To this end, we use zeolitic imidazolate frameworks (ZIF-67) nanosheets derived CoS2, CoP, and Co3O4 with nearly identical morphology and nanostructure to study the compositional effects on their catalytic activities and chemical absorption abilities. Combining with density functional theory calculations and electrochemical screening, we are able to confirm that CoS2 has the highest adsorption energy with polysulfides as well as the strongest catalytic activity toward polysulfides. We believe this work can inspire a more rational way to design efficient catalysts fo...

Modification of the noble metal-based aerogels from the atomic scale is rarely being investigated despite the rapid development of various metallic aerogels. Recent studies have verified that Pd ensembles are more effective than isolated Pd atoms toward electrooxidation of ethanol. However, the electrocatalytic efficiency is still insufficient. Here, for the first time, we successfully anchored Pd-ensembles on the surface of Au2Cu metallic hydrogels via kinetically controlled galvanic displacement reaction. The atomic configuration optimized Au2Cu@Pd metallic aerogels exhibited significantly enhanced mass activity ~ 11.6 times of commercial Pd and excellent stability with remained 90% of mass activity after 300 potential cycle test. The ligand effect and geometric effect generated by the finely tailored atomic configurations including Pd ensembles and core-shell structure are critical for enhancing electrocatalytic efficiencies. Thus, the Pd ensembles anchored-Au2Cu aerogels hold a great promise for being potentially applied in devices such as direct alcohol fuel cells, biosensors and electronics.

We elucidate the structural evolution of CoN

Ir-based nanomaterials are regarded as state-of-the-art cathode electrocatalysts in proton exchange membrane water electrolyzers (PEMWEs). Engineering the morphology of Ir-based three-dimensional architectures as electrocatalysts toward oxygen evolution reaction (OER) has been rarely studied. Here, we report the gelation of IrxCu metallic hydrogels self-assembled with ultrafine and nanovoid incorporated building blocks for enhancing the electrocatalytic performance toward OER. The composition-optimized Ir3Cu metallic aerogels exhibited improved catalytic activity and durability toward OER. The mesosized voids generated through the in situ galvanic replacement reaction and the macrosized porous systems make a great contribution to the increased number of active sites. First-principle calculations revealed the intrinsic optimized binding energy of Ir by alloying with Cu. The best catalytic performance necessities a balance of the adsorption and desorption energy. The well-defined morphology and enhanced OER...

High-efficiency electrocatalysts with superior activity and stability are crucial to practical applications in water splitting, including the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Downsizing the conventional nanoparticle catalyst to single atoms and constructing single-atom catalysts (SACs) is a rapidly emerging research focus. Because of the involvement of unique single-atom active moieties and the strong metal–support interactions arising from interfacial bonding, SACs as promising alternatives to noble metal-based nanoparticle catalysts exhibit profound power in the HER and OER. Here, we present a perspective on the exciting advances of SACs for HER and OER applications, with an emphasis on innovative synthetic strategies and an in-depth understanding of the structure–activity relationship through a combination of systematic characterization and theoretical studies. Finally, the challenges and some of the critical issues in this field are addressed.

Soft robot is a new type of flexible robot which can imitate human hand activity. Electromyographic (EMG) signal is an important bioelectrical signal associated with muscle activity. The innovative combination of soft robot and EMG shows great potential. Based on this inspiration, a humanoid soft robotic hand controlled by EMG was proposed. We designed a single finger 3D model for the soft robotic hand and put forward the three-stage cavity structure. The finite element analysis has been performed to obtain the influence of the geometrical parameters including the number of cavities, the shape of the cavity side section, and the pressure in the cavity on the single finger bending performance. The optimal geometrical parameters were obtained. We analyzed the geometrical deformation of the finger simulation model and figured out the relationship between the input pressure of the soft hand and the angle of bending deformation. In addition, we designed and manufactured the soft robotic hand model and its pneumatic system. Twenty-four effective eigenvalues were extracted from the surface EMG signal (sEMG) of the forearm muscle group and ten-kinds-gestures recognizing system was established. Finally, we realized the online sEMG control of the soft robotic hand, so that the soft robotic hand can reproduce the gestures behavior of human. The correct rate of recognition is 96%. Conclusions obtained in this paper provide theoretical support for the development of humanoid soft robotic hand.

Herein, a ratiometric fluorescence (RF) enzyme-linked immunosorbent assay (RF-ELISA) for sensitive detection of ethyl carbamate (EC) was developed by introducing fluorescent silicon nanoparticles (Si NPs) into the chromogenic substrate system (o-phenylenediamine (OPD)/H 2 O 2 ) of a conventional horseradish peroxidase (HRP)-based ELISA platform to assemble a RF-based signal output system. For this system, the fluorescence of Si NPs at 440 nm (I 440 ) was acted as the reference signal which could be efficiently quenched by 2,3-diaminophenazine (DAP), the HRP-catalyzed oxidation product of OPD; Meanwhile, the fluorescence of DAP at 570 nm (I 570 ) was served as response signal. Therefore, variation in the amount of HRP labeled secondary antibody bound on the microplate which is associated with antibody-antigen recognition events in conventional HRP-based ELISA could be transferred into a more sensitive RF signal (I 570 /I 440 ). On the basis of monoclonal antibody (mAb) which could specifically recognize EC derivative, xanthyl ethyl carbamate (XEC), a Si NPs-based RF-ELISA for EC via a simple pre-analysis derivatization was developed. When detecting the EC content in red wine, this method exhibits a working range from 3.9 to 105.0 μg/L and a limit of detection (LOD) of 2.6 μg/L with excellent specificity, accuracy and reproducibility. The sensitivity is approximately 33-fold higher than that of traditional colorimetric ELISA. The proposed Si NPs-based RF-ELISA is not only highly suitable for screening EC in a large number of samples, but also provides a potential platform for high-throughput and sensitive determination of other analytes for food safety monitoring.

Delicately engineering well-defined noble metal aerogels with favorable structural and compositional features is of vital importance for wide applications. Here, we reported a one-pot and facile method for synthesizing core–shell PdPb@Pd hydrogels/aerogels with multiply-twinned grains and an ordered intermetallic phase using sodium hypophosphite as a multifunctional reducing agent. Due to the accelerated gelation kinetics induced by increased reaction temperature and the specific function of sodium hypophosphite, the formation of hydrogels can be completed within 4 h. Owing to their unique porous structure and favorable geometric and electronic effects, the optimized PdPb@Pd aerogels exhibit enhanced electrochemical performance towards ethylene glycol oxidation with a mass activity of 5.8 times higher than Pd black.

As promising precious metal-free oxygen reduction reaction (ORR) electrocatalysts, Fe–N–C catalysts still face a great challenge to meet the requirement of practical applications. In this study, Fe, S, N-codoped hollow and porous carbon nanorods (Fe–S–N HPCNRs) were designed with the aim of improving the performance of Fe–N–C catalysts from the perspective of composition and structure. They were successfully prepared using cysteine, Fe2+ salt, and polydopamine-encapsulated ZnO nanorods (ZnO NRs@PDA) as precursors by a pyrolysis-acid etching strategy. The hollow and porous structure and composition of Fe, S, N, and C were verified by transmission electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller, and X-ray photoelectron spectroscopy tests. At the optimum ratio of ZnO NRs@PDA/cysteine and pyrolysis temperature, the Fe–S–N HPCNRs display higher ORR activities than the control samples which are lack of one of the precursors. Electrochemical tests show that the ORR follows a 4e pathway with the Fe...

Atomically dispersed and nitrogen-coordinated single iron site catalysts hold great promise to replace platinum for proton-exchange membrane fuel cells, but they suffer from significant performance loss. Now, solving the conundrum to distinguish durable and non-durable FeN4 active sites can guide high-performance catalyst design.

Development of water electrolysis technology is critical to the future of clean energy consumption and storage. Alkaline membrane water electrolysis is very attractive owing to the high energy density of the hydrogen produced and, more importantly, the possibility of lowering system cost by significantly lowering or completely replacing platinum group metal (PGM) catalysts with less expensive metals such as nickel and iron. Replacing perfluorinated membranes with much less expensive hydrocarbon based materials such as oxidation-resistant alkaline membranes and ionomer that are stable under water electrolysis operating conditions will also improve system costs and durability requirements. Previous research has focused on alkaline electrolyzers operating with KOH supporting electrolyte.1 To date, it is clear that alkaline membrane electrolysis is still low technology readiness leveltechnology with reported limitations such as membrane/ionomer durability, non-PGM catalyst performance and durability and previously mentioned, operation with a supporting electrolyte, such as KOH to achieve performance, which adds significant cost to design a corrosion resistant device. In this study, we have developed an alkaline membrane water electrolyzer which operates with pure water and employs non-PGM anode catalyst. Initial focus was to demonstrate membrane and ionomer performance and durability during electrolyzer operation without the use of added electrolyte. We have demonstrated for the first time 500 hours of cell operation with pure water at 500 mA/cm2 and a cell potential of 1.7 V using standard PGM catalysts indicating significant durability. Replacing the iridium oxide with PGM-free catalyst and operating the electrolyzer with pure water will lead to significant cost saving both in catalyst materials and allow for less expensive stainless-steel current collectors. More recently, an alkaline water electrolyzer with iron and nickle based PGM-free based anode catalysts has demonstrated promising performance while operating on pure water. Reference Abbasi, R., Setzler, B. P., Lin, S., Wang, J., Zhao, Y., Xu, H., Pivovar, B., Tian, B., Chen, X., Wu, G., Yan, Y., A Roadmap to Low‐Cost Hydrogen with Hydroxide Exchange Membrane Electrolyzers. Mater.2019, 31, 1805876

Recent years have witnessed a dramatic increase in the production of sustainable and renewable energy. However, the electrochemical performances of the various systems are limited, and there is an intensive search for highly efficient electrocatalysts by more rational control over the size, shape, composition, and structure. Of particular interest are the studies on single-atom catalysts (SACs), which have sparked new interests in electrocatalysis because of their high catalytic activity, stability, selectivity, and 100 % atom utilization. In this Review, we introduce innovative syntheses and characterization techniques for SACs, with a focus on their electrochemical applications in the oxygen reduction/evolution reaction, hydrogen evolution reaction, and hydrocarbon conversion reactions for fuel cells (electrooxidation of methanol, ethanol, and formic acid). The electrocatalytic performance is further considered at an atomic level and the underlying mechanisms are discussed. The ultimate goal is the tailoring of single atoms for electrochemical applications.

Carbon-supported Pt nanostructures currently exhibit great potential in polymer electrolyte membrane fuel cells. Nitrogen-doped hollow carbon spheres (NHCSs) with extra low density and high specific surface area are a promising carbon support for loading Pt NPs. The doped heteroatom of nitrogen not only contributes to the active activity for the oxygen reduction reaction (ORR), but also shows a strong interaction with Pt NPs for entrapping them to prevent dissolution/migration. This synergetic effect/interaction resulted in the uniform dispersion and strong combination of the Pt NPs on the carbon support and thus plays a significant role in hindering the degradation of the catalytic activities of Pt NPs. As expected, the as-obtained Pt/NHCSs displayed improved catalytic activity and superior durability toward the ORR.

In the conventional non-invasive cancer treatments, such as photodynamic therapy (PDT) and photothermal therapy (PTT), light irradiation is precisely focused on tumors to induce apoptosis via the generation of reactive oxygen species (ROS) or localized heating. However, overconsumption of oxygen and restricted diffusion distance of ROS limit the therapeutic effects on hypoxic tumors. Herein, we developed a platform for the rapid uptake of multifunctionalized Au@Pt nanoparticles (NPs) by mitochondria in cancer cells. The mesoporous Au@Pt nanoparticles were labeled with a cell-targeting ligand (folic acid), a mitochondria-targeting group (triphenylphosphine (TPP)), and a photosensitizer (Ce6). This led to significant improvement of the PDT efficacy due to an enhanced cellular uptake, an effective mitochondrial ROS burst, and a rapid intelligent release of oxygen. Moreover, Au@Pt NPs can convert laser radiation into heat, resulting in thermally induced cell damage. This nanosystem could be used as a dual-mode phototherapeutic agent for enhanced cancer therapy and molecular targets associated with disease progression. We achieved a mitochondria-targeted multifunctional therapy strategy (a combination of PDT and PTT) to substantially improve the therapeutic efficiency.

Intermetallic nanocrystals are currently receiving extensive attention due to their well-defined crystal structures, highly ordered atomic distribution and superior structural stability that endow them with optimized catalytic activities, stabilities and high selectivity for use as electrocatalysts for fuel cells. Here, for the first time, we reported the facile synthesis of intermetallic Pd3Pb nanowire networks (IM-Pd3Pb NNs) with a one-step wet-chemical strategy at a relatively low temperature (i.e. 170 °C) in 1 h. The as-prepared IM-Pd3Pb NNs exhibited superior bifunctional catalytic performances toward the oxygen reduction reaction (ORR) and the ethanol oxidation reaction (EtOR) compared to commercial Pt/C and Pd black, respectively. Significantly, IM-Pd3Pb NNs also showed excellent methanol- and CO-tolerant ability as ORR cathode and EtOR anode electrocatalysts, respectively. The electrochemically active surface area and mass activity of IM-Pd3Pb NNs are about 3.4 times and 2 times higher than those of Pd black toward the EtOR, respectively. As the Pt-free bifunctional electrocatalysts, 3D IM-Pd3Pb architectures with exceptional catalytic performances hold great promise in various applications such as energy conversion and storage devices, sensors, electronics, optics and so on.

Among the emerging energy storage methods, lithium–sulfur (LIS) batteries have drawn plenty of attention due to their high theoretical energy density, low cost and environmental benignity. Nevertheless, the insulating nature of sulfur and notorious polysulfide shuttling result in low sulfur utilization and short cycling life. In recent years, various carbon structures have been reported as effective sulfur hosts to tolerate volume expansion, prevent polysulfide dissolution and enhance electrical conductivity. It is hard for carbon materials, however, to satisfy all these aspects with a simple structural design. Thus, developing hierarchical carbon structures that serve as a multi-functional host is necessary for high-performance LIS batteries. Herein, we reported a facile method to prepare a three-dimensional carbon nanofiber (3DCNF) through a hydrothermal reaction. With the structural advantages, the 3DCNF and sulfur composite delivered a capacity as high as 1266 and 977 mA h g−1 at 0.1 and 0.5 C, respectively. After 500 cycles at 0.5 C, it still retains a capacity of 607 mA h g−1 (0.07% capacity fading per cycle), exhibiting excellent cycling capability.

Recently, metallic hydrogels/aerogels have received tremendous attention due to their unique physical and chemical properties. For the first time, we reported the successful synthesis of AuPtx metallic hydrogels at 60 °C in 2–4 h. Surfactant-free AuPt5 metallic hydrogels displayed enhanced electrocatalytic activities and stabilities toward methanol oxidation.

The oxygen evolution reaction (OER) is a kinetically sluggish anodic reaction and requires a large overpotential to deliver appreciable current. Despite the fact that non-precious metal-based alkaline water electrocatalysts are receiving increased attention, noble metal-based electrocatalysts (NMEs) applied in proton exchange membrane water electrolyzers still have advantageous features of larger current and power densities with lower stack cost. Engineering NMEs for OER catalysis with high efficiency, durability and utilization rate is of vital importance in promoting the development of cost-effective renewable energy production and conversion devices. In this tutorial review, we covered the recent progress in the composition and structure optimization of NMEs for OER including Ir- and Ru-based oxides and alloys, and noble-metals beyond Ir and Ru with a variety of morphologies. To shed light on the fundamental science and mechanisms behind composition/structure–performance relationships and activity–stability relationships, integrated experimental and theoretical studies were pursued for illuminating the metal–support interaction, size effect, heteroatom doping effect, phase transformation, degradation processes and single-atom catalysis. Finally, the challenges and outlook are provided for guiding the rational engineering of OER electrocatalysts for applications in renewable energy-related devices.

Due to robustness, easy large-scale preparation and low cost, nanomaterials with enzyme-like characteristics (defined as ‘nanozymes’) are attracting increasing interest for various applications. However, most of currently developed nanozymes show much lower activity in comparison with natural enzymes, and the deficiency greatly hinders their use in sensing and biomedicine. Single-atom catalysts (SACs) offer the unique feature of maximum atomic utilization, providing a potential pathway to improve the catalytic activity of nanozymes. Herein, we propose a Fe-N-C single-atom nanozyme (SAN) that exhibits unprecedented peroxidase-mimicking activity. The SAN consists of atomically dispersed Fe─N(x) moieties hosted by metal–organic frameworks (MOF) derived porous carbon. Thanks to the 100% single-atom active Fe dispersion and the large surface area of the porous support, the Fe-N-C SAN provided a specific activity of 57.76 U mg(−1), which was almost at the same level as natural horseradish peroxidase (HRP). Attractively, the SAN presented much better storage stability and robustness against harsh environments. As a proof-of-concept application, highly sensitive biosensing of butyrylcholinesterase (BChE) activity using the Fe-N-C SAN as a substitute for natural HRP was further verified.

A simple and rapid process of ReO

The conversion reaction-based lithium-sulfur battery features an attractive energy density of 2600 W h/kg. Nevertheless, the unsatisfied performance in terms of poor discharge capacity and cycling stability still hinders its practical applications. Recently, porous carbon materials have been widely reported as promising sulfur reservoirs to promote the sluggish reaction kinetics of sulfur conversion, tolerate volume expansion of sulfur, and suppress polysulfide shuttling. However, porous carbon with a simply designed nanostructure is hard to satisfy all of these aspects simultaneously. Herein, we have applied a dual-template strategy that assembles carbon pores into carbon sheets to prepare three-dimensional (3D) nitrogen-doped porous carbon nanosheets (N-PCSs) as the multifunctional sulfur host for the Li-S battery. By arranging carbon pores within an interconnected 3D architecture, the porous carbon sheets enable rapid electron/ion transfer. Moreover, the micro/mesopores and nitrogen dopant in N-PCS provide both physical and chemical restrictions to polysulfide species. With these advances, the N-PCS/S cathode delivers a large initial discharge capacity of 1360 mA h/g at 0.1 C. When performed at 0.5 C for 1000 cycles, the cathode can still remain ∼50% of its capacity with a low decay rate of 0.05% per cycle, showing the important role of the 3D carbon material in the Li-S battery.

Oxygen evolution reaction (OER) plays a vital role in electrochemical water splitting, leading to a more feasible route for sustainably and eco-friendly producing hydrogen energy. Rather than noble metal catalysts with scarcity and expense, first raw 3d dual transition metal non-oxides are promising candidates to achieve superior OER activity and durability in alkaline solution due to their tunable electron structure, high conductivity, and cost-off advantages. Herein, a concise review of recent advances in designing 3d dual transition metal non-oxides electrocatalysts for OER under alkaline condition is provided with particular emphasis on structure-performance relationships. The diverse effects of 3d dual transition metals, especially for Ti, V, Mn, Fe, Co, Ni, Cu, and Zn, are highlighted in discussion regarding synthesis strategies and OER performances of corresponding electrocatalysts, in different categories of transition metal sulfides, selenides, phosphides, nitrides, and other non-oxides. Finally, existent challenges and directional perspectives for developing first raw 3d dual transition metal non-oxides electrocatalysts with outstanding OER performance are outlined.

Currently, three-dimensional self-supported metallic structures are attractive for their unique properties of high porosity, low density, excellent conductivity, etc., that promote their wide application in fuel cells. Here, for the first time, we report a facile synthesis of Au@Pt3Pd ternary metallic aerogels with a unique dendritic core–shell structure via a one-pot self-assembly gelation strategy. This strategy is simple and saves time without any concentration or destabilizer steps. The as-prepared Au@Pt3Pd ternary metallic aerogels demonstrated enhanced electrochemical performance toward the oxygen reduction reaction compared to that of commercial Pt/C. The unique dendritic core–shell structures, Pt3Pd alloyed shells, and cross-linked network structures are beneficial for the electrochemical oxygen reduction reaction via the electronic effect, geometric effect, and synergistic effect. This strategy of fabrication of metallic hydrogels and aerogels as well as their exceptional properties holds great p...

To accelerate hydrogel formation and further simplify the synthetic procedure, a series of MCu (M = Pd, Pt, and Au) bimetallic aerogels is synthesized from the in situ reduction of metal precursors through enhancement of the gelation kinetics at elevated temperature. Moreover, the resultant PdCu aerogel with ultrathin nanowire networks exhibits excellent electrocatalytic performance toward ethanol oxidation, holding promise in fuel-cell applications.

Finding an approach to synthesize low cost catalysts with high activity and improved durability is the main challenge for the commercialization of proton exchange membrane fuel cells. The electrocatalytic performance of Pt-based catalysts could be improved significantly by accurately controlling the particle size, morphology and composition. In this work, PtCu bimetallic nanofoams, composed of fused nanoparticles with ∼3 nm in diameter, were synthesized using a one-step reduction method. After dealloying with nitric acid, the PtCu@Pt core–shell bimetallic nanofoams were 7-fold more active in terms of mass activity, 14 times more active on the basis of specific activity, and more durable for ORR than the commercial Pt/C catalyst, which hold great promise in fuel cell applications.

Porous 3D graphene-based hybrid materials (3D GBHMs) are currently attractive nanomaterials employed in the field of energy. Heteroatom-doped 3D graphene and metal, metal oxide, and polymer-decorated 3D graphene with modified electronic and atomic structures provide promising performance as electrode materials in energy storage and conversion. Numerous synthesis methods such as self-assembly, templating, electrochemical deposition, and supercritical CO2, pave the way to mass production of 3D GBHMs in the commercialization of energy devices. This review summarizes recent advances in the fabrication of 3D GBHMs with well-defined architectures such as finely controlled pore sizes, heteroatom doping types and levels. Moreover, current progress toward applications in fuel cells, supercapacitors and batteries employing 3D GBHMs is also highlighted, along with the detailed mechanisms of the enhanced electrochemical performance. Furthermore, current critical issues, challenges and future prospects with respect to applications of 3D GBHMs in practical devices are discussed at the end of this review.

In this work, we synthesized a series of core@shell Au2r@Agt nanoparticles (CS Au2r@Agt NPs) with defined but varied Au core diameter (2r) and Ag shell thickness (t) via overgrowth of Ag on preformed Au NPs at room temperature. We demonstrate that the surface enhanced Raman scattering (SERS) activity of as-prepared Au2r@Agt NPs is dependent on the Ag shell thickness (t). The critical t value (tc), above which Au2r@Agt NPs reach the maximal SERS activity, can be empirically correlated with the r values as tc = 0.301·r + 0.695 when the diameters of Au cores (2r) are smaller than 42 nm, the mean free path of bulk gold, while the tc is fixed at about 3 nm when 2r > 42 nm. The simple empirical rule should be very useful for the design of Au@Ag NPs for SERS applications, which is hardly discussed in the literature.

A facile wet chemistry method was developed for the synthesis of PtCu bimetallic alloy nanotubes with controllable composition and porous surfaces by employing Te nanowire as a hard template. Due to the synergetic effect among the components as well as their one-dimensional porous nanostructure, the PtCu nanotubes present enhanced electrocatalytic activity and durability for oxygen reduction reaction in acid solution. The mass activity and specific activity of Pt76Cu24 reach 0.41 A mgPt−1 and 0.83 mA cm−2, and are about 3 and 5 times higher than that of Pt/C catalysts. The bimetallic alloys could be considered as an excellent candidate for electrocatalysts and other potential applications.

Fe-Based atomically dispersed single site catalysts are the state of the art platinum group metal (PGM)-free catalysts in proton exchange membrane fuel cells (PEMFC). However, due to the Fenton reactions potentially causing degradation of ionomers and membranes, Fe content in PGM-free catalysts must be minimized. Therefore, development low-Fe or Fe-free cathode catalysts are urgently needed for durable and inexpensive PEMFCs. Based on our previous effort to develop nitrogen‐coordinated single Co atom catalyst derived from Co‐doped metal‐organic frameworks (MOFs) [1,2], in this presentation, we will further discuss our recent effort to elucidate the formation mechanisms of CoNx sited driven by thermal treatment. Also we will introduce our new progress to prepare electronspun Co catalysts and binary CoFe catalysts for oxygen reduction in acidic electrolytes. Detailed synthesis procedure, extensive characterization, and RDE activity and fuel cell performance will be discussed. References (1) Wang, X. X.; Cullen, D. A.; Pan, Y.-T.; Hwang, S.; Wang, M.; Feng, Z.; Wang, J.; Engelhard, M. H.; Zhang, H.; He, Y.et al. Nitrogen-Coordinated Single Cobalt Atom Catalysts for Oxygen Reduction in Proton Exchange Membrane Fuel Cells. Advanced Materials 2018, 30 (11), 1706758. (2) He, Y.; Hwang, S.; Cullen, D. A.; Uddin, M. A.; Langhorst, L.; Li, B.; Karakalos, S.; Kropf, A. J.; Wegener, E. C.; Sokolowski, J.et al. Highly active atomically dispersed CoN4 fuel cell cathode catalysts derived from surfactant-assisted MOFs: carbon-shell confinement strategy. Energy & Environmental Science 2019, 12 (1), 250.