Active and Durable Hydrogen Evolution Reaction Catalyst Derived from Pd-Doped Metal-Organic Frameworks

Nanoengineered, Pd-doped Co@C nanoparticles as an effective electrocatalyst for OER in alkaline seawater electrolysis

Water electrolysis is considered one of the major sources of green hydrogen as the fuel of the future. However, due to limited freshwater resources, more interest has been geared toward seawater electrolysis for hydrogen production. The development of effective and selective electrocatalysts from earth-abundant elements for oxygen evolution reaction (OER) as the bottleneck for seawater electrolysis is highly desirable. This work introduces novel Pd-doped Co nanoparticles encapsulated in graphite carbon shell electrode (Pd-doped CoNPs@C shell) as a highly active OER electrocatalyst towards alkaline seawater oxidation, which outperforms the state-of-the-art catalyst, RuO2. Significantly, Pd-doped CoNPs@C shell electrode exhibiting low OER overpotential of ≈213, ≈372, and ≈ 429 mV at 10, 50, and 100 mA/cm2, respectively together with a small Tafel slope of ≈ 120 mV/dec than pure Co@C and Pd@C electrode in alkaline seawater media. The high catalytic activity at the aforementioned current density reveals decent selectivity, thus obviating the evolution of chloride reaction (CER), i.e., ∼490 mV, as competitive to the OER. Results indicated that Pd-doped Co nanoparticles encapsulated in graphite carbon shell (Pd-doped CoNPs@C electrode) could be a very promising candidate for seawater electrolysis.

Octahedral Pd3Cu7 Catalysts on Diverse Support Materials for Efficient Hydrogen Evolution: Theoretical Investigation and Mechanistic Perspective

This work showcases a novel strategy for the synthesis of shape-dependent alloy nanostructures with the incorporation of solid substrates, leading to remarkable enhancements in the electrocatalytic performance. Herein, an aqueous medium approach has been used to synthesize an octahedral PdXCuY alloy of different Pd:Cu ratios to better comprehend their electrocatalytic potential. With the aim to outperform high activity and efficient stability, zirconium oxide (ZrO2), graphene oxide nanosheets (GONs), and hexagonal boron nitride nanosheets (hBNNs) solid substrates are occupied to decorate the optimized Pd3Cu7 catalyst with a minimum 5 wt % metal loading. When compared to the counterparts and different ratios, the Pd3Cu7@hBNNs catalyst exhibited an optimal activity for hydrogen evolution reaction (HER). The lower overpotential and Tafel values observed are 64 and 51 mV/dec for Pd3Cu7@hBNNs followed by Pd3Cu7@ZrO2, which showed a 171 mV overpotential and a 98 mV/dec Tafel value, respectively. Meanwhile, the Pd3Cu7@GONs were found to have a 202 mV overpotential and a 110 mV/dec Tafel value. The density functional theory, which achieves a lower free energy (ΔGH*) value for Pd3Cu7@hBNNs than the other catalysts for HER, further supports its excellent performance in achieving the Volmer-Heyrovsky mechanism path. Moreover, the superior HER activity and sturdier resilience after 8 h of stability may be due to the synergy between the metal atoms, monodisperse decoration, and the coordination effect of the support material.

Molecular dynamics study on the thermodynamic stability and structural evolution of crown-jewel structured PdCu nanoalloys

The novel crown-jewel (CJ) structured PdCu nanoalloys have attracted considerable interest in high-performance single-atom catalysis. The characteristics of demanding high-temperature calcination in the synthesis of these samples disable us from experimentally understanding the details of the thermal evolution behavior of PdCu nanoclusters during the heating process. In this work, by analyses of potential energy surface, bond order parameter, and radial distribution function, we have theoretically studied the thermodynamic stabilities and structural evolution of Pd-decorated Cu-based CJ nanoclusters with various compositions and sizes by molecular dynamics simulations. PdCu nanoclusters undergo a cuboctahedral (Cubo) to icosahedral (Ico) structural transformation before melting. This transformation is size- and Pd-composition dependent. The small size and high Pd-composition of PdCu nanoclusters facilitate this transformation. In addition, we find that the surface and interface effects of clusters have an important impact on the structural transformation and Cubo-Ico structural transformation is strongly related to the release of excess energy.

The role of various components in Ru-NiCo alloys in boosting the performance of overall water splitting

Understanding the synergistic mechanism of multi-component alloys is crucial and challenging for overall water splitting. Herein, Ru-NiCo_0.5-600 °C and Ru-Ni_0.75Co with excellent electrocatalytic activity are designed and synthesized. The Ru-NiCo_0.5-600 °C alloy exhibits remarkable HER activity with an overpotential of 42, 77 and 93 mV at 10 mA cm^-2 in alkaline, acidic and neutral conditions, and the Ru-Ni_0.75Co electrocatalyst presents outstanding OER activity with an overpotential of 176 mV at 10 mA cm^-2 in 1.0 M KOH. The Ru-NiCo_0.5-600 °C ||Ru-Ni_0.75Co cell requires only 1.48 and 1.69 V to reach 10 and 100 mA cm^-2 towards overall water splitting. A series of experiments reveal that the strong electronic coupling among Ru, Ni and Co regulates the electronic structure and enhances the intrinsic catalytic activity and stability of the as-synthesized Ru-NiCo electrocatalysts. Systematic experimental and theoretical results prove that Ni atoms act as the active sites of dissociating water, while Ru and Co are respectively the active centers of proton and hydroxyl adsorption for HER and OER. Our work provides a new perspective for profoundly understanding the synergistic effect of multi-component alloys towards water splitting.

Pd-Co-Based Electrodes for Hydrogen Production by Water Splitting in Acidic Media

To realize the benefits of a hydrogen economy, hydrogen must be produced cleanly, efficiently and affordably from renewable resources and, preferentially, close to the end-users. The goal is a sustainable cycle of hydrogen production and use: in the first stage of the cycle, hydrogen is produced from renewable resources and then used to feed a fuel cell. This cycle produces no pollution and no greenhouse gases. In this context, the development of electrolyzers producing high-purity hydrogen with a high efficiency and low cost is of great importance. Electrode materials play a fundamental role in influencing electrolyzer performances; consequently, in recent years considerable efforts have been made to obtain highly efficient and inexpensive catalyst materials. To reach both goals, we have developed electrodes based on Pd-Co alloys to be potentially used in the PEMEL electrolyzer. In fact, the Pd-Co alloy is a valid alternative to Pt for hydrogen evolution. The alloys were electrodeposited using two different types of support: carbon paper, to fabricate a porous structure, and anodic alumina membrane, to obtain regular arrays of nanowires. The goal was to obtain electrodes with very large active surface areas and a small amount of material. The research demonstrates that the electrochemical method is an ideal technique to obtain materials with good performances for the hydrogen evolution reaction. The Pd-Co alloy composition can be controlled by adjusting electrodeposition parameters (bath composition, current density and deposition time). The main results concerning the fabrication process and the characterization are presented and the performance in acid conditions is discussed.

Single source precursor route for the first graphene oxide-Pd6P nanocomposite: application in electrochemical hydrogen evolution reaction

For the first time, Pd₆P has been synthesised using a simple, straightforward and one-pot method i.e., thermolysis of a Pd(II) complex of a bidentate (P, N) organophosphorus ligand (anthracene-9-yl-CHN-CH₂CH₂-PPh₂). The electrocatalyst (obtained after grafting nanospheres of Pd₆P over layers of graphene oxide) shows high activity in electrochemical hydrogen evolution reactions (HER) with an overpotential of 133 mV to drive 10 mA cm^-2 of cathodic current density. The GO-Pd₆P nanocomposite is robust and effective for a continuous HER run for up to 16 hours.

Green application of trimetallic nickel-cobalt-molybdenum nanocomposites on 3D graphene oxide as a powerful electrocatalyst for hydrogen evolution reaction

In-situ designing of multiple metals electrocatalysts with high active sites and performance is the main challenge for hydrogen evolution reaction (HER). So in this work, 3D-rGO was easily obtained from 2D-graphene by a simple one-step hydrothermal method to create the interspace sites and active surface area. The Ni-Co-Mo tri-metallic@3D-rGO was synthesized and fully characterized by different techniques, e.g., FT-IR, XRD, Raman, FE-SEM, TEM, EDS, mapping, ICP-OES, AFM, voltammetry, and electrochemical impedance spectroscopy. According to the FE-SEM and TEM images, the Ni-Co-Mo tri-metallic@3D-rGO has a crumpled-formed structure. The as-prepared nanocomposite has high HER performance with a low potential of -0.11 (vs. RHE) to deliver 10 mA cm^-2 and Tafel slope of 68 mV dec^-1 for Pt and -0.25 V (vs. RHE) to deliver 10 mA cm^-2 and Tafel slope of 110 mV dec^-1 for graphite counter electrode. Furthermore, the 3D structure illustrates high long-term durability in the HER process for 1000 continuous cycles and 12 h operation at -0.42 V (vs. RHE) for Pt and graphite counter electrode. It's noticeable HER performance has the synergetic effect between 3D-rGO and tri-metallic structure with high porosity and electrical conductivity, enhancing HER kinetic.

RuCo Alloy Nanoparticles Embedded into N-Doped Carbon for High Efficiency Hydrogen Evolution Electrocatalyst

For large-scale and sustainable water electrolysis, it is of great significance to develop cheap and efficient electrocatalysts that can replace platinum. Currently, it is difficult for most catalysts to combine high activity and stability. To solve this problem, we use cobalt to regulate the electronic structure of ruthenium to achieve high activity, and use carbon matrix to protect alloy nanoparticles to achieve high stability. Herein, based on the zeolitic imidazolate frameworks (ZIFs), a novel hybrid composed of RuCo alloy nano-particles and N-doped carbon was prepared via a facile pyrolysis-displacement-sintering strategy. Due to the unique porous structure and multi-component synergy, the optimal RuCo500@NC750 material in both acidic and alkaline media exhibited eminent HER catalytic activity. Notably, the 3-RuCo500@NC750 obtained a current density of 10 mA cm−2 at 22 mV and 31 mV in 0.5 M H2SO4 and 1.0 M KOH, respectively, comparable to that of the reference Pt/C catalyst. Furthermore, the Tafel slopes of the catalyst are 52 mV Dec−1 and 47 mV Dec−1, respectively, under acid and alkali conditions, and the catalyst has good stability, indicating that it has broad application prospects in practical electrolytic systems. This work contributes to understanding the role of carbon-supported polymetallic alloy in the electrocatalytic hydrogen evolution process, and provides some inspiration for the development of a high efficiency hydrogen evolution catalyst.

Theoretical Insights into the Hydrogen Evolution Reaction on VGe2N4 and NbGe2N4 Monolayers

Catalytically active sites at the basal plane of two-dimensional monolayers for hydrogen evolution reaction (HER) are important for the mass production of hydrogen. The structural, electronic, and catalytic properties of two-dimensional VGe₂N₄ and NbGe₂N₄ monolayers are demonstrated using the first-principles calculations. The dynamical stability is confirmed through phonon calculations, followed by computation of the electronic structure employing the hybrid functional HSE06 and PBE+U. Here, we introduced two strategies, strain and doping, to tune their catalytic properties toward HER. Our results show that the HER activity of VGe₂N₄ and NbGe₂N₄ monolayers are sensitive to the applied strain. A 3% tensile strain results in the adsorption Gibbs free energy (ΔG _H*) of hydrogen for the NbGe₂N₄ monolayer of 0.015 eV, indicating better activity than Pt (-0.09 eV). At the compressive strain of 3%, the ΔG _H* value is -0.09 eV for the VGe₂N₄ monolayer, which is comparable to that of Pt. The exchange current density for the P doping at the N site of the NbGe₂N₄ monolayer makes it a promising electrocatalyst for HER (ΔG _H* = 0.11 eV). Our findings imply the great potential of the VGe₂N₄ and NbGe₂N₄ monolayers as electrocatalysts for HER activity.

Catalytic activity, thermal stability and structural evolution of PdCu single-atom alloy catalysts: the effects of size and morphology

Single-atom alloys (SAAs) have been emerging as an important field of research in electrocatalysis owing to extremely high atom utilization, unique structure and high catalytic activity. In this work, the catalytic properties and thermal stability of PdCu SAAs with a crown-jewel (CJ) structure are studied by density functional theory (DFT) calculations and the molecular dynamics (MD) simulation method. The DFT results reveal that CJ-structured PdCu SAAs show excellent HER and ORR catalytic performance, and can be regarded as a promising alternative to Pt catalysts towards the ORR or HER. Additionally, we attempt to explain the high catalytic activity of PdCu SAAs by electronic structure analysis. In addition, MD simulation results confirm the thermal stability of CJ-structured PdCu. More importantly, we found that CJ-structured PdCu clusters undergo a structural transformation from cuboctahedral (Cubo) to icosahedral (Ico) structure by heating or after the adsorption of reaction intermediate, which indicates that Cubo is less stable than the Ico structure. Besides, Cubo-Ico transformation is size-dependent and only found in small clusters. Furthermore, the effects of size and morphology on melting properties are discussed. The melting point increases as cluster size increases, which agrees well with Pawlow's law.

Emerging carbon shell-encapsulated metal nanocatalysts for fuel cells and water electrolysis

The development of low-cost, high-efficiency electrocatalysts is of primary importance for hydrogen energy technology. Noble metal-based catalysts have been extensively studied for decades; however, activity and durability issues still remain a challenge. In recent years, carbon shell-encapsulated metal (M@C) catalysts have drawn great attention as novel materials for water electrolysis and fuel cell applications. These electrochemical reactions are governed mainly by interfacial charge transfer between the core metal and the outer carbon shell, which alters the electronic structure of the catalyst surface. Furthermore, the rationally designed and fine-tuned carbon shell plays a very interesting role as a protective layer or molecular sieve layer to improve the performance and durability of energy conversion systems. Herein, we review recent advances in the use of M@C type nanocatalysts for extensive applications in fuel cells and water electrolysis with a focus on the structural design and electronic structure modulation of carbon shell-encapsulated metal/alloys. Finally, we highlight the current challenges and future perspectives of these catalytic materials and related technologies in this field.

NH2-MIL-125(Ti) doped CdS/Graphene composite as electro and photo catalyst in basic medium under light irradiation

The development of active electrocatalysts and photocatalysts for hydrogen evolution reaction (HER) and for environmental remediation is a huge challenge. Research is still underway on the development of low-cost catalytic materials with appreciable efficiency for HER. In the present study, a composite of metal organic framework (MOF) with CdS and graphene (NH₂-MIL-125(Ti)/CdS-graphene) composites were developed with different loadings of graphene material via solvothermal technique. Further the electrocatalytic activity of the synthesized catalysts were investigated for HER and photocatalytic degradation of dye. Results show that the synthesized catalyst with a less amount of graphene was more active. HER results showed a less Tafel slope of 70.8 and 61.9 mVdec^-1 with 15.6 mA/cm² and 15.46 mA/cm² current densities under light on and off conditions. Further the dye degradation activity of the synthesized catalysts was tested with Rhodamine B dye and results showed that the catalyst showed excellent activity for low weight loading of graphene with a degradation efficiency of 95 % and followed pseudo first order kinetic model. Overall results showed that the synthesized composites are promising for HER and photocatalytic applications.

Palladinized graphene oxide-MOF induced coupling of Volmer and Heyrovsky mechanisms, for the amplification of the electrocatalytic efficiency of hydrogen evolution reaction

In this study, a nanocomposite of palladium supported graphene oxide (GO)/metal–organic framework (MOF) was prepared using electroless deposition of Pd on GO followed by impregnation method of Pd@GO and MOF. The prepared materials were characterized with various analytical techniques and their applications as HER electrocatalysts were evaluated using cyclic voltammetry (CV), Tafel plots, and turn over frequencies (TOFs). The HER results showed a radical increment of H₂ production in the nanocomposite through the Volmer reaction together with Heyrovsky or Tafel mechanism. This disclosed that the addition of Pd@GO/MOF in the electrolytic system possessed better catalytic characteristics with enhanced current density which may open a new way for hydrogen production and storage via HER.

Recent advances in catalytic systems in the prism of physicochemical properties to remediate toxic CO pollutants: A state-of-the-art review

Carbon monoxide (CO) is the most harmful pollutant in the air, causing environmental issues and adversely affecting humans and the vegetation and then raises global warming indirectly. CO oxidation is one of the most effective methods of reducing CO by converting it into carbon dioxide (CO₂) using a suitable catalytic system, due to its simplicity and great value for pollution control. The CO oxidation reaction has been widely studied in various applications, including proton-exchange membrane fuel cell technology and catalytic converters. CO oxidation has also been of great academic interest over the last few decades as a model reaction. Many review studies have been produced on catalysts development for CO oxidation, emphasizing noble metal catalysts, the configuration of catalysts, process parameter influence, and the deactivation of catalysts. Nevertheless, there is still some gap in a state of the art knowledge devoted exclusively to synergistic interactions between catalytic activity and physicochemical properties. In an effort to fill this gap, this analysis updates and clarifies innovations for various latest developed catalytic CO oxidation systems with contemporary evaluation and the synergistic relationship between oxygen vacancies, strong metal-support interaction, particle size, metal dispersion, chemical composition acidity/basicity, reducibility, porosity, and surface area. This review study is useful for environmentalists, scientists, and experts working on mitigating the harmful effects of CO on both academic and commercial levels in the research and development sectors.

Palladium cobalt alloy encapsulated in carbon nanofibers as bifunctional electrocatalyst for high-efficiency overall hydrazine splitting

Electrolytic water splitting is a promising strategy to generate clean hydrogen energy but still restricted by the sluggish kinetics during the anodic oxygen evolution reaction (OER). A highly efficient route to significantlyreduce the cell voltage of electrolytic water splitting is to replace OER with hydrazine oxidation reaction (HzOR) so as to assist hydrogen generation effectively. Here, we report the fabrication of carbon nanofibers (CNFs) embedded with palladium cobalt (PdCo) alloy nanoparticles, via an electrospinning followed by a carbonization treatment. The as-synthesized PdCo-CNFs catalyst displays a superior electrocatalytic activity toward HzOR with a working potential of 258 mV (vs. RHE) to drive a current density of 50 mA cm^-2 in an alkaline solution with 0.2 M hydrazine. Furthermore, the favorable hydrogen evolution reaction (HER) activity of this catalyst enables it highly efficient electrolytic hydrogen production, and the two-electrode system using PdCo-CNFs as both the cathode and anode for overall hydrazine splitting is capable of delivering a cell voltage of 0.440 V to attain 10 mA cm^-2, which is 1.496 V less than that for pure water splitting using the same electrodes and even 0.459 V less than the overall hydrazine splitting device using Pt/C//RuO₂ as electrocatalysts. This work provides a reliable way for the fabrication of promising bifunctional electrocatalysts to promote energy-saving hydrogen production for practical applications.

Bimetallic ZIF-Derived Co/N-Codoped Porous Carbon Supported Ruthenium Catalysts for Highly Efficient Hydrogen Evolution Reaction

Exploring the economical, powerful, and durable electrocatalysts for hydrogen evolution reaction (HER) is highly required for practical application. Herein, nanoclusters-decorated ruthenium, cobalt nanoparticles, and nitrogen codoped porous carbon (Ru-pCo@NC) are prepared with bimetallic zeolite imidazole frameworks (ZnCo-ZIF) as the precursor. Thus, the prepared Ru-pCo@NC catalyst with a low Ru loading of 3.13 wt% exhibits impressive HER catalytic behavior in 1 M KOH, with an overpotential of only 30 mV at the current density of 10 mA cm-2, Tafel slope as low as 32.1 mV dec-1, and superior stability for long-time running with a commercial 20 wt% Pt/C. The excellent electrocatalytic properties are primarily by virtue of the highly specific surface area and porosity of carbon support, uniformly dispersed Ru active species, and rapid reaction kinetics of the interaction between Ru and O.

Recent Advances in Amino-Based Molecules Assisted Control of Noble-Metal Electrocatalysts

Morphology-control synthesis is an effective means to tailor surface structure of noble-metal nanocrystals, which offers a sensitive knob for tuning their electrocatalytic properties. The functional molecules are often indispensable in the morphology-control synthesis through preferential adsorption on specific crystal facets, or controlling certain crystal growth directions. In this review, the recent progress in morphology-control synthesis of noble-metal nanocrystals assisted by amino-based functional molecules for electrocatalytic applications are focused on. Although a mass of noble-metal nanocrystals with different morphologies have been reported, few review studies have been published related to amino-based molecules assisted control strategy. A full understanding for the key roles of amino-based molecules in the morphology-control synthesis is still necessary. As a result, the explicit roles and mechanisms of various types of amino-based molecules, including amino-based small molecules and amino-based polymers, in morphology-control of noble-metal nanocrystals are summarized and discussed in detail. Also presented in this progress are unique electrocatalytic properties of various shaped noble-metal nanocrystals. Particularly, the optimization of electrocatalytic selectivity induced by specific amino-based functional molecules (e.g., polyallylamine and polyethyleneimine) is highlighted. At the end, some critical prospects, and challenges in terms of amino-based molecules-controlled synthesis and electrocatalytic applications are proposed.

Prussian Blue Analogs and Their Derived Nanomaterials for Electrochemical Energy Storage and Electrocatalysis

Prussian blue analogs (PBAs), the oldest artificial cyanide-based coordination polymers, possess open framework structures, large specific surface areas, uniform metal active sites, and tunable composition, showing significant perspective in electrochemical energy storage. These electrochemically active materials have also been converted to various functional metal containing nanomaterials, including carbon encapsulated metals/metal alloys, metal oxides, metal sulfides, metal phosphides, etc. originating from the multi-element compositions as well as elaborate structure design. In this paper, a comprehensive review will be presented on the recent progresses in the development of PBA frameworks and their derivatives based electrode materials and electrocatalysts for electrochemical energy storage and conversion. In particular, it will focus on the synthesis of representative nanostructures, the structure design, and figure out the correlation between nanomaterials structure and electrochemical performance. Lastly, critical scientific challenges in this research area are also discussed and perspective directions for the future research in this field are provided, in order to provide a brand new vision into the further development of novel active materials for the next-generation advanced electrochemical devices.

Tuning the surface using palladium based metallosurfactant for hydrogen evolution reaction

Synthesis of a novel electrocatalyst for hydrogen evolution reaction (HER) is highly demanding for renewable energy production. This research reports the design and development of novel palladium based metallosurfactant (PdCPC(I)) that belongs to the unique class of inorganic-organic hybrid with striking structural features that are explored for the first time in the HER. The formation of the micelle, molecular orientation and surface characteristics of the metallosurfactant are calculated by conductivity and contact angle measurements. The reduction of palladium in metallomicelles during electrolysis accelerates the HER. Metallosurfactant makes the substrate hydrophilic, which in turn enhances the activity of the modified substrate. The 269 mV and 400 mV (vs RHE) overpotential is required to achieve the 10 mA cm^-2 of current density for PdCPC(I) and CPC, respectively. Tafel slope of PdCPC(I) is 57 mV dec^-1, which signifies that the reaction follows the Volmer- Heyrovsky mechanism in the presence of catalyst. The presence of the palladium in the core of the micelle is certified by ICPMS study. The present electrocatalyst also demonstrates 40 h of electrochemical durability. This work opens the doors toward the enhancement of HER, which fulfills the dreams for future energy resources.

DNA-based low resistance palladium nano-spheres for effective hydrogen evolution reaction

Highly stable and less resistance Pd/DNA NSs are designed for HER in acidic medium and require a low overpotential (η10) of 79 mV. DNA plays multiple roles such as stabilizer, structure-directing agent and binder in the fabrication of electrodes.

Investigating affordable cobalt based metallosurfactant as an efficient electrocatalyst for hydrogen evolution reaction

The implementation of hydrogen evolution reaction (HER) is an essential requirement of a stable electrocatalyst that competes for the performance of noble metals (Pt, Pd), especially in acidic conditions. This research reports the design and development of affordable cobalt (Co) based metallosurfactant (CoCPC(I)) which performs under acidic medium (0.5 N H₂SO₄) for HER. Such a fabricated catalyst is able to lower the cathodic potentials efficiently and exhibits 130 mV onset potential and Tafel slope of 104 mVdec^-1 that depicts the presence of Volmer-Heyrovsky mechanism. The results of the studies confirm that our synthesized metallosurfactant forms metallomicelles on the surface of electrode and surface remains stable even after the electrochemical cycle. Further, the surfactant protects the metal centre as an active site for a longer time via forming metallo-micelles which helps to sustain activity. These outcomes reveal the efficient mass and charge transfer capability of CoCPC(I) which results in faster charge transfer kinetics. Therefore, the utilization of Co based metallosurfactant can split water easily, cost-effectively, and without using hazardous chemicals. Our demonstrated technology seems suitable for industrial applications due to features of large-scale production possibilities.

Metal-organic framework templated Pd/CeO2@N-doped carbon for low-temperature CO oxidation

A new Pd/Ce based metal-organic framework is designed and synthesized as a self-sacrificial template for fabrication of an efficient catalyst for CO oxidation. The catalyst obtained by thermal annealing at 700 °C (Pd/CeO₂@NC-700) is composed of N-doped carbon with embedded Pd and CeO₂ nanoparticles, which are highly dispersed and closely connected in the N-doped carbon; the high Pd loading (33.7 wt%) and the coupling between Pd and the CeO₂ phase synergistically boost the CO oxidation performance. The Pd/CeO₂@NC-700 catalyst exhibits a 100% conversion temperature of 89 °C and excellent long-term stability. By combining structural characterization with density functional theory calculations, two possible CO oxidation pathways of TPB and TOP are revealed, in which the adsorbed O₂ directly dissociates to O* atoms and activates CO* molecules. The transfer of O* between Pd and Ce (TPB) or Pd and Pd (TOP) facilitates the formation of intermediates and finally results in the production of CO₂. This work provides a new insight into the development of novel efficient catalysts for CO oxidation based on metal-organic frameworks.

IrCo alloy nanoparticles supported on N-doped carbon for hydrogen evolution electrocatalysis in acidic and alkaline electrolytes

Designing efficient and low-cost electrocatalysts for the hydrogen evolution reaction (HER) is of great importance to advance water splitting technology towards practical applications. Herein, we report the preparation of IrCo nanoparticles supported on nitrogen-doped carbon (IrCo/NC) as a HER electrocatalyst in acidic and alkaline electrolytes. The IrCo/NC composite is obtained by pyrolyzing an Ir-doped Co(OH)2 precursor on g-C3N4, and is endowed with N-doped carbon and uniform IrCo alloy nanoparticles via a crystal confinement resulting from the Ir-doping into the Co(OH)2 layer. Electrocatalytic analysis shows that the IrCo/NC electrode requires low overpotentials of 32 mV at 10 mA cm-2 in 0.5 M H2SO4 and 33 mV in 1 M KOH, which are superior to those of the Co/NC and IrCo alloys that are free of Ir-doping or N-doped carbon. The results provide a strategy for designing and preparing active noble-transition bimetallic alloy electrocatalysts as efficient HER catalysts.

Metal-Organic Frameworks for Hydrogen Energy Applications: Advances and Challenges

Hydrogen is in limelight as an environmental benign alternative to fossil fuels from few decades. To bring the concept of hydrogen economy from academic labs to real world certain challenges need to be addressed in the areas of hydrogen production, storage, and its use in fuel cells. Crystalline metal-organic frameworks (MOFs) with unprecedented surface areas are considered as potential materials for addressing the challenges in each of these three areas. MOFs combine the diverse chemistry of molecular linkers with their ability to coordinate to metal ions and clusters. The unabated flurry of research using MOFs in the context of hydrogen energy related activities in the past decade demonstrates the versatility of this class of materials. In the present review, we discuss major strategical advances that have taken place in the field of "hydrogen economy and MOFs" and point out issues requiring further attention.

Tuning the Activity of Carbon for Electrocatalytic Hydrogen Evolution via an Iridium-Cobalt Alloy Core Encapsulated in Nitrogen-Doped Carbon Cages

Graphene, a 2D material consisting of a single layer of sp² -hybridized carbon, exhibits inert activity as an electrocatalyst, while the incorporation of heteroatoms (such as N) into the framework can tune its electronic properties. Because of the different electronegativity between N and C atoms, electrons will transfer from C to N in N-doped graphene nanosheets, changing inert C atoms adjacent to the N-dopants into active sites. Notwithstanding the achieved progress, its intrinsic activity in acidic media is still far from Pt/C. Here, a facile annealing strategy is adopted for Ir-doped metal-organic frameworks to synthesize IrCo nanoalloys encapsulated in N-doped graphene layers. The highly active electrocatalyst, with remarkably reduced Ir loading (1.56 wt%), achieves an ultralow Tafel slope of 23 mV dec^-1 and an overpotential of only 24 mV at a current density of 10 mA cm^-2 in 0.5 m sulfuric acid solution. Such superior performance is even superior to the noble-metal catalyst Pt. Surface structural and computational studies reveal that the superior behavior originates from the decreased ΔG_H* for HER induced by the electrons transferred from the alloy core to the graphene layers, which is beneficial for enhancing CH binding.

An overview on Pd-based electrocatalysts for the hydrogen evolution reaction

The electrochemical hydrogen evolution reaction (HER) is a well-studied reaction which involves the reduction of protons for hydrogen production. Pd-based compounds are expected to have activity on par with or better than the expensive state-of-the-art Pt and can be considered as the future materials for the HER.

Rapid Adsorption Enables Interface Engineering of PdMnCo Alloy/Nitrogen-Doped Carbon as Highly Efficient Electrocatalysts for Hydrogen Evolution Reaction

The catalytic performance of Pd-based catalysts has long been hindered by surface contamination, particle agglomeration, and lack of rational structural design. Here we report a simple adsorption method for rapid synthesis (∼90 s) of structure-optimized Pd alloy supported on nitrogen-doped carbon without the use of surfactants or extra reducing agents. The material shows much lower overpotential than 30 wt % Pd/C and 40 wt % Pt/C catalysts while exhibiting excellent durability (80 h). Moreover, unveiled by the density functional theory (DFT) calculation results, the underlying reason for the outstanding performance is that the PdMnCo alloy/pyridinic nitrogen-doped carbon interfaces weaken the hydrogen-adsorption energy on the catalyst and thus optimize the Gibbs free energy of the intermediate state (ΔG_H*), leading to a remarkable electrocatalytic activity. This work also opens up an avenue for quick synthesis of a highly efficient structure-optimized Pd-based catalyst.

Nanoporous PtFe Nanoparticles Supported on N-Doped Porous Carbon Sheets Derived from Metal-Organic Frameworks as Highly Efficient and Durable Oxygen Reduction Reaction Catalysts

Designing and exploring catalysts with high activity and stability for oxygen reduction reaction (ORR) at the cathode in acidic environments is imperative for the industrialization of proton exchange membrane fuel cells (PEMFCs). Theoretical calculations and experiments have demonstrated that alloying Pt with a transition metal can not only cut down the usage of scarce Pt metal but also improve performance of mass activity compared with pure Pt. Herein, we exhibit the preparation of nanoporous PtFe nanoparticles (np-PtFe NPs) supported on N-doped porous carbon sheets (NPCS) via facile in situ thermolysis of a Pt-modified Fe-based metal-organic framework (MOF). The np-PtFe/NPCS exhibit a more positive half-wave potential (0.92 V) compared with commercial Pt/C catalyst (0.883 V). The nanoporous structure allows our catalyst to possess high mass activity, which is found to be 0.533 A·mg_Pt^-1 and 3.04 times better than that of Pt/C (0.175 A·mg_Pt^-1). Moreover, the conversion of PtFe NPs from porous to hollow structure can maintain the activity of electrocatalyst. Our strategy provides a facile design and synthesis process of noble-transition metal alloy electrocatalysts via noble metal modified MOFs as precursors.

Ruthenium-cobalt nanoalloys encapsulated in nitrogen-doped graphene as active electrocatalysts for producing hydrogen in alkaline media

The scalable production of hydrogen could conveniently be realized by alkaline water electrolysis. Currently, the major challenge confronting hydrogen evolution reaction (HER) is lacking inexpensive alternatives to platinum-based electrocatalysts. Here we report a high-efficient and stable electrocatalyst composed of ruthenium and cobalt bimetallic nanoalloy encapsulated in nitrogen-doped graphene layers. The catalysts display remarkable performance with low overpotentials of only 28 and 218 mV at 10 and 100 mA cm⁻², respectively, and excellent stability of 10,000 cycles. Ruthenium is the cheapest platinum-group metal and its amount in the catalyst is only 3.58 wt.%, showing the catalyst high activity at a very competitive price. Density functional theory calculations reveal that the introduction of ruthenium atoms into cobalt core can improve the efficiency of electron transfer from alloy core to graphene shell, beneficial for enhancing carbon–hydrogen bond, thereby lowing ΔG_H* of HER.

Ruthenium is the cheapest platinum-group metal, yet active hydrogen evolution catalysts with low amounts of ruthenium have yet to be designed. Here, the authors report the preparation of a ruthenium–cobalt nanoalloy and demonstrate its potential as an effective hydrogen evolution catalyst in basic media.

A versatile stimulus-responsive metal-organic framework for size/morphology tunable hollow mesoporous silica and pH-triggered drug delivery

Metal-organic frameworks (MOFs) have spurred tremendous research interest in the fields of nanoscience and nanotechnology. However, exploring their biomedical applications is still a daunting challenge. In this work, we employed an acid-degradable MOF, zeolitic imidazolate framework-8 (ZIF-8), both as a self-sacrificial template to synthesize uniform size/morphology-controllable hollow mesoporous silica materials (HMSNs) and as a mesopore blocker for fabricating a pH-responsive HMSN-based drug delivery system. Starting from the ZIF-8 template, a layer of mesoporous silica is coated on ZIF-8 and subsequently the template was self-degraded under acidic conditions to obtain HMSNs. A series of monodisperse HMSNs ranging from ca. 80 nm to ca. 3000 nm with morphologies that give rare examples of cubic and dodecahedral morphologies has been prepared. It is demonstrated that the as-made HMSNs possess well-defined mesopores, huge cavities and good biocompatibility, which make them favourable for drug delivery. So, ZIF-8 was then grafted onto the HMSN to block the pore orifice for pH-responsive intracellular anticancer drug release. The results indicated that the ZIF-8-coated HMSN with encapsulated doxorubicin hydrochloride (DOX) was an efficient drug delivery vehicle in cancer therapy using pH-responsive release. This strategy sheds new light on the application of MOF materials and provides great potential for biomedical applications.

Enhanced Activity for Hydrogen Evolution Reaction over CoFe Catalysts by Alloying with Small Amount of Pt

The hydrogen evolution reaction highly relied on Pt electrocatalysts, with high activity and stability. In the past few years, a host of efforts have been made in the development of novel platinum nanostructures with a low amount of Pt because the scarcity and high price of Pt hinder its practical applications. Here, we report the preparation of PtCoFe@CN electrocatalysts with a remarkably reduced Pt loading amount of 4.60% by annealing Pt-doped metal-organic frameworks (MOFs). The electrocatalyst demonstrated an outstanding performance with only 45 mV overpotential to achieve the 10 mA cm^-2 current density, which is quite close to that of the commercial 20% Pt/C catalyst. The enhanced catalytic capability is originated from the modification of the electronic structures of CoFe by alloying with Pt. The results indicate that robust and superstable alloy electrocatalysts which contain a very small amount of noble metal could be prepared by annealing noble metal-doped MOFs.

A platinum(ii)–palladium(ii)–nickel(ii) heterotrimetallic coordination polymer showing a cooperative effect on catalytic hydrogen evolution

Stepwise construction of a 1D heterotrimetallic coordination polymer containing all three group 10 metal ions and its heterogeneous catalytic activity for electrochemical hydrogen evolution are reported.