Noble Metal-free Electrocatalysts Research Articles

Boron-Doped Graphene Quantum Dots Anchored to Carbon Nanotubes as Noble Metal-Free Electrocatalysts of Uric Acid for a Wearable Sweat Sensor

Boron-Doped Graphene Quantum Dots Anchored to Carbon Nanotubes as Noble Metal-Free Electrocatalysts of Uric Acid for a Wearable Sweat Sensor

Understanding electron transfer processes and oxygen reduction electrocatalysis in nanocrystalline Cu-MOF-74

Metal-organic frameworks (MOFs) with redox properties are potentially good candidates as noble-metal free electrocatalysts due to their high specific surface area, uniform pore size and shape, and high dispersion of redox centers. Copper-based MOFs are particularly interesting as oxygen reduction electrocatalysts due to the well-known bio-affinity of this element towards oxygen in oxygen-reducing proteins. In this line, the metal–organic framework Cu-MOF-74, which has open metal sites in its 3D structure has not been studied up to date as electrocatalyst for the oxygen reduction reaction (ORR). This work reports an exhaustive electrochemical analysis of nanocrystalline Cu-MOF-74, for assessing its electrochemical behavior and electrocatalytic performance for the ORR. Nanocrystals of Cu-MOF-74 (about 40 nm in size) with intercrystal mesoporosity and high surface area (>1000 m2g−1) were synthesized by a previously reported procedure. The study of this material supported on glassy carbon (GC) rotating disk electrodes allowed to prove its good stability in neutral electrolytic medium and an efficient connectivity of the open Cu centers with redox ability. Moreover, GC/Cu-MOF-74 electrodes were capable to efficient electro-reduce dissolved oxygen to water at overpotentials higher than −0.62 V, fully preserving the framework integrity after long-time assays. It was also verified that this four-electron process is mediated by the reduction of Cu centers exposed at the inner walls of the MOF pores, involving electro-adsorbed oxygenated intermediates. The location of the active sites inside the deep structural nanopores strongly affects the mass transport properties and is detrimental for the whole performance as ORR electrocatalyst. Thus, while the results reported here provide new evidences on the redox and electrocatalytic behavior of nanocrystalline Cu-MOF-74, it is clear that its configuration must be rethought in order to attain an acceptable ORR performance.

Mo2C regulated by cobalt components doping in N-doped hollow carbon nanofibers as an efficient electrocatalyst for hydrogen evolution reaction

Hydrogen is a viable substitute to fossil fuels and electrochemically catalyzed hydrogen evolution has attracted wide attention due to its stability and effectiveness. Nevertheless it is still a major challenge to design and prepare highly active noble metal-free electrocatalysts with controllable structure and composition for efficient hydrogen evolution reaction (HER). Herein, Mo2C regulated by cobalt components (Co and CoO) doping in N-doped hollow carbon nanofibers (marked as Mo2C/Co/CoO-NHCNFs) are firstly designed and prepared via a facile coaxial electrospinning followed by calcination process. The one-dimensional conductive carbon host, hollow structure and synergistic effect among CoO, Co and Mo2C can jointly promote electron transfer, augment exposure of active sites and adjust the electronic structure of the active sites, resulting in the excellent of HER performances. The optimized catalyst has a high specific surface area of 101.27 m2 g−1. Meanwhile, it has a low overpotential of 143 mV at a current density of 10 mA cm−2 and a small Tafel slope of 74 mV dec−1 in 1.0 M KOH.Satisfactorily, the overpotential is reduced by 231 mV at the same current density compared with Mo2C doped in N-doped carbon nanofibers (named as Mo2C-NCNFs). Moreover, the Mo2C/Co/CoO-NHCNFs also demonstrate superior long-term stability. The formative mechanism of Mo2C/Co/CoO-NHCNFs is expounded, and the construction technique is established. The design philosophy and the simple and economical method are of significance for development of HER electrocatalysts.

Facile Single Step Electrochemical Growth of Ni3P on Carbon Cloth for Highly Efficient Hydrogen Evolution Reaction

The exploration of facile synthesis, a highly active and cost-effective noble metal-free durable electrocatalyst for hydrogen production through water electrolysis is an essential job in the arena of sustainable and clean energy production. In this context, it is crucially desired to look for an inexpensive noble metal-free electrocatalyst for practical use. In recent studies, nickel phosphides are the widely investigated hydrogen evolution reaction (HER) electrocatalysts owing to their extraordinary electronic properties, corrosion-resistant ability and superior electrocatalytic response. In this study, a highly ordered single-phase Ni3P is grown on activated carbon cloth (CC*) via a one-step electrochemical deposition method, which offers a facile synthesis route for the development of a highly durable electrocatalyst active towards HER. The hierarchical porous structure of Ni3P provides effluent ion dynamic channels that encourage expeditious kinetics, superior activity and extraordinary stability. The resulting electrocatalyst (Ni3P@CC*) shows astonishing electrochemical activity towards HER under alkaline conditions and delivers an overpotential of 150 mV at a current density of 10 mA cm−2 with high durability and large electrochemically active surface area (ECSA) that favours the large-scale hydrogen production for future energy systems.

Controllable Assembly of Vanadium-Containing Polyoxoniobate-Based Materials and Their Electrocatalytic Activity for Selective Benzyl Alcohol Oxidation.

During the controllable synthesis of two vanadium-containing Keggin-type polyoxoniobates (PONbs), [Ni(en)2]5[PNb12O40(VO)5](OH)5·18H2O (1) and [Ni(en)3]5[PNb12O40(VO)2]∙17H2O (2, en = ethylenediamine) are realized by changing the vanadium source and hydrothermal temperature. Compounds 1 and 2 have been thoroughly characterized by single-crystal X-ray diffraction analysis, FT-IR spectra, X-ray photoelectron spectrum (XPS), powder X-ray diffraction (PXRD), etc. Compound 1 contains a penta-capped Keggin-type polyoxoniobate {PNb12O40(VO)5}, which is connected by adjacent [Ni(en)2]2+ units into a three-dimensional (3D) organic-inorganic framework, representing the first nickel complexes connected vanadoniobate-based 3D material. Compound 2 is a discrete di-capped Keggin-type polyoxoniobate {PNb12O40(VO)2} with [Ni(en)3]2+ units as counter cations. Compounds 1 and 2 have poor solubility in common solvents and can keep stable in the pH range of 4 to 14. Notably, both 1 and 2 as electrode materials are active for the selective oxidation of benzyl alcohol to benzaldehyde. Under ambient conditions without adding an alkaline additive, compound 1 as a noble metal free electrocatalyst can achieve 92% conversion of benzyl alcohol, giving a Faraday efficiency of 93%; comparatively, 2 converted 79% of the substrate with a Faraday efficiency of 84%. The control experiments indicate that both the alkaline polyoxoniobate cluster and the capped vanadium atoms play an important role during the electrocatalytic oxidation process.

Low-temperature synthesized Mo2C and novel Mo2C–MnO2 heterostructure for highly efficient hydrogen evolution reaction and high-performance capacitors

Here, a facile and cost-effective way is proposed to synthesize Mo2C nanoparticles and Mo2C/MnO2 heterostructures by utilizing laboratory waste. The Mo2C nanoparticles are well encapsulated by graphitic carbon layers, which provide high cyclic and structural stability to Mo2C. The electrochemical hydrogen evolution reaction (HER) activity and capacitive properties of these samples are studied in detail. Mo2C synthesized at 500 °C exhibits higher HER activity with a Tafel slope of 79 mV dec−1. To further improve the HER activity of Mo2C nanoparticles, the heterostructure of Mo2C and MnO2 is developed. The optimized Mo2C/MnO2 (2:1) heterostructure delivers a current density of 10 mA cm−2 at a low overpotential of 58.3 mV and shows a very low Tafel slope of 36 mV dec−1. It exhibited long-term cyclic stability up to 5000 cyclic voltammetry (CV) cycles. This paper describes a novel and effective method for fabricating noble metal-free HER electrocatalysts utilizing laboratory waste as a carbon precursor.

Dual-phase MoS2/MXene/CNT ternary nanohybrids for efficient electrocatalytic hydrogen evolution

Two-dimensional (2D) molybdenum disulfide (MoS2) has been recognized as a potential substitution of platinum (Pt) for electrochemical hydrogen evolution reaction (HER). However, the broad adoption of MoS2 is hindered by its limited number of active sites and low inherent electrical conductivity. In this work, we employed a one-step solvothermal synthesis technique to construct a ternary hybrid structure consisting of dual-phase MoS2, titanium carbide (Ti3C2) MXene, and carbon nanotubes (CNTs), and demonstrated synergistic effects for active site exposure, surface area enlargement, and electrical conductivity improvement of the catalyst. The dual-phase MoS2 (DP-MoS2) is directly formed on the MXene with CNTs acting as crosslinks between 2D islands. The existence of edge-enriched metallic phase MoS2, the conductive backbone of MXene along with the crosslink function of CNTs clearly improves the overall HER performance of the ternary nanocomposite. Moreover, the integration of MoS2 with MXene not only increases the interlayer distance of the 2D layers but also partially suppresses the MXene oxidation and the 2D layer restacking, leading to good catalytic stability. As a result, an overpotential of 169 mV and a low Tafel slope of 51 mV/dec was successfully achieved. This work paves a way for 2D-based electrocatalyst engineering and sheds light on the development of the next-generation noble metal-free HER electrocatalysts.

N-doped bimetallic sulfides hollow spheres derived from metal-organic frameworks toward cost-efficient and high performance oxygen evolution reaction

The development of noble-metal free electrocatalysts with high activity for water splitting is crucial to address the severe energy issue, while the poor conductivity and catalytic stability hinder their commercialization. Traditional heteroatom doping and structural design is still unsatisfactory due to the high cost. Herein, the Ni-based metal–organic framework (Ni-MOF) was used as precursor and self-template, and a series of N-doped Ni-Co bimetallic sulfides (N-NixCoy-S) were synthesized using oil bath plus solvothermal method. The as-prepared sulfide displayed hollow sphere structure with a diameter of 300–500 nm. The electrocatalytic activity was investigated using a typical three-electrode system (Hg/HgO and carbon rod as reference electrode and counter electrode, respectively). By optimizing the Ni/Co ratio, the precisely tailored N-Ni1Co4-S material delivered superior oxygen evolution reaction (OER) performances with a low overpotential of 286.2 ± 2.4 mV at current density of 10 mA cm−2 in 1 M KOH solution (pH = 13.5). Such the catalyst can further exhibit a long-term catalytic stability with almost no decay during 36 h in KOH electrolyte. It demonstrates that this work develops an effective strategy to obtain high-performance and cost-effective electrocatalyst for the water splitting application.

Controllable Synthesis of a Loofah-Like Cobalt-Nickel Selenide Network as an Efficient Electrocatalyst for the Hydrogen Evolution Reaction.

The rational design and construction of noble metal-free electrocatalysts featuring high efficiency and low cost are important for the hydrogen evolution reaction (HER). A significant development in the synthesis of a loofah-like Co0.6Ni0.4Se2 architecture (expressed as Co0.6Ni0.4Se2-LN) electrocatalyst on carbon cloth through a three-step method is reported. Both the ionic liquid 1-dodecyl-3-methylimidazolium acetate (IL, [C12MIm]Ac) and the molar ratio of Co to Ni play a pivotal role in the synthesis of Co0.6Ni0.4Se2-LN with 3D hierarchical architecture. Co0.6Ni0.4Se2-LN exposes abundant active sites and provides hierarchical and stable transfer channels for both electrolyte ions and electrons, which results in outstanding HER performance. Impressively, Co0.6Ni0.4Se2-LN shows a low overpotential of 163 mV at 10 mA cm-2, a small Tafel slope of 40 mV dec-1, and superior stability to continuously catalyze the generation of H2 for 40 h. This study offers a new perspective to the synthesis of high-efficiency inexpensive electrocatalysts for HER and also presents a good example for investigating the potential application of ILs in the synthesis of functional materials.

Heterostructured CoP·CoMoP nanocages as advanced electrocatalysts for efficient hydrogen evolution over a wide pH range

A sustainable and environmental-friendly method to produce hydrogen with high purity is the electrochemical water splitting, but its commercialization is challenged due to lack of cost-effective electrocatalysts for hydrogen evolution reaction (HER) over a wide pH range. Herein, a series of CoP·xCoMoP heterostructured nanocages (NCs) were prepared via a dissolution-regrowth and subsequent phosphorization process using metal-organic frameworks (MOFs) as template. The three-dimensional (3D) architecture of CoP·xCoMoP is constituted by the heterostructured nanosheets composed with CoP and CoMoP phase. These noble-metal-free earth-abundant transition metal phosphide (TMP) catalysts show a pH-universal HER activity with high efficiency. Under the optimal atom ratio of Co and Mo (6:5), CoP·5CoMoP NC catalysts can deliver a current density of 10 mA cm−2 at the overpotential of 72 mV with a Tafel slope of 60.3 mV dec−1 in 1.0 M KOH solution. The same current output requires overpotential of 44 mV in 0.5 M H2SO4 solution and 151 mV in1.0 M phosphate buffered solution (PBS), respectively. The superior HER activity of CoP·5CoMoP NC catalysts can be comparable to or even better than most of noble metal-free HER electrocatalysts reported recently. In addition, CoP·5CoMoP NC catalysts also show a fairly high HER stability over a wide pH range, and their HER activity can be well kept without significant loss for long-term electrolysis. The 3D CoP·5CoMoP heterostructured catalysts hold promise as efficient and low-cost catalysts for water splitting devices over a wide pH range.

Compositional and crystallographic design of Ni-Co phosphide heterointerfaced nanowires for high-rate, stable hydrogen generation at industry-relevant electrolysis current densities

Lack of high-performance noble-metal free electrocatalysts for hydrogen evolution reaction (HER) to exceed the benchmark Pt-based electrocatalysts, still remains a major hurdle on the way to clean hydrogen economy. Here we rationally, atomistically design and synthesize the hetero-interfaced Ni-Co phosphide nanowires which deliver exceptional activity and stability in water electrolysis under industry-relevant current densities. The compositional and crystallographic design produces extra-stable Ni5P4-Co2P nanowires sprouting from a Ni-Co alloy foam (NCF). The extraordinary reactivity is ensured by the heterointerfaces between the highly-active (303) crystal planes of Co2P and Ni5P4 nanowire phases. The overpotentials of Ni5P4-Co2P/NCF catalysts at −10, −100, and −1000 mA cm−2 are about 21, 92 and 267 mV in 1 M KOH, respectively, far exceeding the commercial Pt/C catalysts. The Tafel slope of Ni5P4-Co2P/NCF catalyst is only 23 mV dec−1, indicating an even faster HER kinetic compared to Pt/C (32 mV dec−1). Moreover, the Ni5P4-Co2P/NCF catalyst shows an ultra-stable and lasting performance, evidenced by only a minor 3.6% drop at j250 after 100 h continuing operation. The DFT calculations confirm that the exposed heterointerfaces between (303) planes of Ni5P4 and Co2P phases play a key role for boosting the HER activity of Ni5P4-Co2P electrocatalyst.

Insights into the Effect of Precursors on the FeP-Catalyzed Hydrogen Evolution Reaction.

Iron phosphide nanoparticles (NPs) are promising noble metal-free electrocatalysts for the hydrogen evolution reaction (HER), but they usually show inferior activity due to the limited surface area and oxidative passivation. We reported a facile synthetic method to prepare FeP hollow NPs (HNPs) with various precursors. It was proven that the structural parameters (i.e., size, phosphating temperature, phase, and surfactant) of oxide precursors were correlated to the electrochemically active surface area (ECSA), phase purity, surface oxidation, and hollow morphology of FeP HER catalysts, thus affecting the HER activity. Among the three FeP HNPs, the 9 nm FeP HNPs prepared using the Fe3O4 precursor exhibited the highest overall activity with the lowest overpotential of 76 mV to drive a cathodic current density of 10 mA·cm-2 due to the highest ECSA, while 25 nm FeP prepared using the Fe2O3 precursor showed the highest turnover frequency because of the high phase purity and low surface oxidation degree.

Conducting scaffold supported defect rich 3D rGO-CNT/MoS2 nanostructure for efficient HER electrocatalyst at variable pH

Designing a suitable noble metal-free electrocatalyst for the hydrogen evolution reaction (HER) is enduring challenge. Molybdenum disulfide (MoS 2 ) shows structural and electronic advantages as potential HER electrocatalyst. The structural and electronic design of MoS 2 electrocatalysts should be considered to improve the efficiency and stability of MoS 2 based electrodes. This report shows that the presence of synergistic interaction significantly improves the HER electrocatalytic activity of defect-rich 3D rGO-CNT/MoS 2 composites. The Defect-rich conductive scaffold supported nanostructures can improve the catalytic performance and stability. Lowering of the HOMO-LUMO gap supervises the charge transfer resistance of the nanostructure . The turnover frequency value indicates that 3D rGO-CNT/MoS 2 acts as the potential electrocatalyst and the overpotential observed at a current density of 10 mA cm −2 in acidic and alkaline media are 88 mV and 172 mV, respectively. This investigation provides a new idea to develop molybdenum disulfide and scaffolds based 3D nanostructures to improve the inherent electrocatalytic activity of HER. • Synthesis of conducting scaffold supported 3D rGO-CNT/MoS 2 nanostructure. • Physicochemical analysis leads to defect rich nanostructure with different S/Mo ratio. • Formation of conducting scaffold based nanocomposite enhance HER activity. • 3D nanostructure provide extra operational stability in acidic and alkaline pH.

Heterostructured ferroelectric BaTiO3@MOF-Fe/Co electrocatalysts for efficient oxygen evolution reaction

We present a simple route to creating anBTO200@MOF-Fe/Co heterostructures for efficient OER, but also provide a unique platform for designing superior, noble metal-free OER electrocatalysts via incorporating ferroelectric, high-κ nanomaterials.

Boron-Doped Graphene Quantum Dots Anchored Carbon Nanotubes as a Noble Metal-Free Electrocatalyst of Uric Acid for Wearable Sweat Sensor

Boron-Doped Graphene Quantum Dots Anchored Carbon Nanotubes as a Noble Metal-Free Electrocatalyst of Uric Acid for Wearable Sweat Sensor

Engineering transition metal catalysts for large-current-density water splitting.

Electrochemical water splitting plays a crucial role in transferring electricity to hydrogen fuel and appropriate electrocatalysts are crucial to satisfy the strict industrial demand. However, the successfully developed non-noble metal catalysts have a small tested range and the current density is usually less than 100 mA cm-2, which is still far away from the practical application standards. Aiming to provide guidance for the fabrication of more advanced electrocatalysts with a large current density, we herein systematically summarize the recent progress achieved in the field of cost-efficient and large-current-density electrocatalyst design. Beginning by illustrating the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) mechanisms, we elaborate on the concurrent issues of non-noble metal catalysts that are required to be addressed. In view of large-current-density operating conditions, some distinctive features with regard to good electrical conductivity, high intrinsic activity, rich active sites, and porous architecture are also summarized. Next, some representative large-current-density electrocatalysts are classified. Finally, we discuss the challenges associated with large-current-density water electrolysis and future pathways in the hope of guiding the future development of more efficient non-noble-metal catalysts to boost large-scale hydrogen production with less electricity consumption.

Boron-Doped Graphene Quantum Dots Anchored Carbon Nanotubes as a Noble Metal-Free Electrocatalyst of Uric Acid for Wearable Sweat Sensor

Boron-Doped Graphene Quantum Dots Anchored Carbon Nanotubes as a Noble Metal-Free Electrocatalyst of Uric Acid for Wearable Sweat Sensor

Bismuth-doped cobaltosic oxide as a noble-metal free electrocatalyst for the efficient methanol oxidation reaction

BackgroundMethanol electro-oxidation reactions (MOR) are utilized to provide electricity in direct methanol fuel cells (DMFC), which requires a reasonable design of catalysts to accelerate sluggish MOR. Herein, a series of cobalt oxides have been doped with a foreign oxophilic transition metal (Bi) by the sol-gel method and further calcination treatment. MethodsThe composition and structure of Bi0.13Co2.87O4-550 were characterized by the scanning electron microscopy (SEM), the powder X-ray diffraction (XRD), and X-ray photoelectron spectra (XPS). Evaluate the electrocatalytic performance of materials by cyclic voltammetry, chronoamperometry, and impedance spectroscopy. Significant findingsBy virtue of the tunable compositional and structural advantages, the optimized Bi0.13Co2.87O4-550 nanocomposite shows the excellent electrocatalytic activity, very high mass activity (808.5 mA mg−1), as well as remarkable durability to resist CO poisoning during methanol oxidation. The excellent electrocatalytic activity for MOR is attributed to the high specific surface area, abundant active sites and superior mass transportability. Furthermore, the oxidation of other alcohols including ethanol, ethylene glycol and glycerol are also realized by the electrocatalysis of Bi0.13Co2.87O4-550. This work provides a good idea for the design of non-precious metal electrocatalysts with the high performance.

Defect stabilized Fe atom on porous BN sheet as a potential electrocatalyst for oxygen reduction reaction: A first-principles investigation

The slow kinetics of the cathodic oxygen reduction reduction (ORR) remain a significant issue in the development of polymer electrolyte membrane fuel cells (FCs). In this study, Fe-doped porous BN (p-BN) nanosheet is proposed as an efficient and noble-metal free electrocatalyst for the ORR process in FCs using first-principles calculations. The calculated formation energies show that the Fe atom is more stable on the p-BN with a boron vacancy than one with a nitrogen vacancy. The ORR process on this electrocatalyst begins with the cleavage of the OO bond of chemisorbed O2, followed by the hydrogenation of the separated O atoms to produce two water molecules. The rate-determining step in the ORR process is the formation of the second H2O molecule with an energy barrier of 1.12 eV. As a result, ORR prefers a direct four-electron route on the Fe-doped p-BN catalyst. Our findings can help in the design and manufacturing of novel electrocatalysts for ORRin FCs.

Engineering interfacial coupling between 3D net-like Ni3(VO4)2 ultrathin nanosheets and MoS2 on carbon fiber cloth for boostinghydrogen evolution reaction

The use of cheap and efficient electrocatalyst for the production of hydrogen is the key to solving the current energy crisis. Herein, we used a two-step hydrothermal process to fabricate noble-metal-free 3D net-like Ni3(VO4)2 ultrathin nanosheets coupled with MoS2@CFC interface. Unlike the traditional two-dimensional composite materials, Ni3(VO4)2 ultrathin nanosheets intersect with MoS2 nanosheets grown on CFC in a 3D net-like structure (Ni3(VO4)2/MoS2@CFC). Due to the mutual combination of structures and the interfacial coupling cooperation effect between Ni3(VO4)2 nanosheet and MoS2@CFC, the catalytically active area was expanded, and the intrinsic activity toward HER was significantly improved. Ni3(VO4)2/MoS2@CFC showed high activity at the industrial temperature (75 °C), with an overpotential of 77 mV (10 mA/cm2) and a 65 mV/dec Tafel slope. This material showed good stability at 0.5 M H2SO4. This work provides a heterostructure scheme for the construction of a novel noble metal-free electrocatalyst to promote hydrogen evolution reaction.