A new durable and high performance platinum supported on Ag–Ni-porous coordination polymer as an anodic DMFC nano-electrocatalyst: DFT and experimental investigation

Due to the poor performance and intermediates poisoning of available catalysts in direct methanol fuel cells (DMFC), the researcher is confronted with a considerable challenge for obtaining modified electrocatalyst. Ag–Ni porous coordination polymer (ANP) as a new electrocatalyst supporter was synthesized by a hydrothermal method. To achieve favorable electrocatalyst for DMFC systems, platinum nanoparticles was deposited upon ANP by an electrochemical method and platinum supported on Ag–Ni porous coordination polymer (Pt-ANP) was formed. Fourier transform infrared spectroscopy (FTIR) analysis ensured correct synthesized of ANP and Pt-ANP. In addition, the morphologies investigation of ANP and Pt-ANP were carried out by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The FE-SEM images indicate that the platinum nanoparticles have been greatly deposited on ANP surface. Electrochemical behaviors of prepared catalyst for methanol oxidation were evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and chronoamperometry (CA) techniques. Electrochemical cyclic voltammetry tests (CV) indicate that the forward peak current density of Pt-ANP is about 105 mA/cm² which it is 33% more than the forward peak current density of pure Pt catalyst (70.21 mA/cm²). Moreover, electrochemical surface area (ECSA) of Pt-ANP is 26.42 m²/g_Pt. In addition, density functional theory (DFT) computations show that with the deposition of Pt upon ANP, the HOMO-LOMO energy gap of ANP has been decreased which they are suitable for electrochemical reactions. Theoretical results are greatly in accordance with the experiments. Based on the results, Pt-ANP could be a superior electrocatalyst for methanol oxidation.     

Preparation of Pd/ZnO/Ni hierarchical porous array film with enhanced electrocatalytic activity for methanol oxidation

In this study, we successfully synthesized a Pd/ZnO/Ni hierarchical porous array-film catalyst by electrodeposition and magnetron sputtering with the assistance of the monodisperse colloidal sphere template. Structural characterisation indicated that a layer of Pd nanoparticles was uniformly grown on the ZnO/Ni ordered bowl-like micro/nano array film. Electrochemical measurements in alkaline solution demonstrated that the as-grown array film had outstanding electrocatalytic activity for methanol oxidation. The specific activity of the Pd/ZnO/Ni porous array film was up to 130.1 mA cm⁻². The corresponding mass activity (812.7 mA mg⁻¹) was 6 times higher than that of commercial Pd/C catalyst (134.8 mA mg⁻¹), and the stability was also much better than the commercial one. These excellent electrochemical properties can be attributed to the unique hierarchical porous structure, which offers a high specific surface area for the methanol reaction, and ZnO intermediate layer, which effectively removes the poisoning species from the Pd sites through the strong oxidative hydroxyl radicals.     

In situ surface dealumination of intermetallic NiFe aluminides electrocatalysts for enhancing the oxygen evolution

Herein, based on the mechanical alloying (MA) and in situ electrochemical etching methods, a series of porous Ni–Fe electrocatalysts with different Ni/Fe atomic ratios derived from intermetallic NiFe aluminides have been designed and applied to OER (oxygen evolution reaction) in alkaline solution. As comparing with bulk NiFe aluminides electrocatalyst, the porous electrocatalyst presents higher activity via the etching method. In addition, among all porous samples with different metal stoichiometric ratios, Ni_2/3Fe_1/3Al shows the highest OER activity with an overpotential of 299 mV at 10 mA cm^?2 and a Tafel slope of 58.9 mV dec^?1, which can be attributed to the high intrinsic activity and large electrochemical surface area from the leaching of Al. This work provides a promising route to in situ synthesize highly efficient electrocatalysts for water splitting.     

Reduced graphene oxide-supported Ni-MoxC electrocatalyst for hydrogen evolution reaction prepared by ultrasonication and lyophilization

A Ni and Mo_xC hybrid (Ni-Mo_xC) supported on N-doped reduced graphene oxide (N-rGO) electrocatalyst with high hydrogen evolution reaction (HER) activity was prepared by ultrasonication and lyophilization. Notably, benefiting from the synergistic effect between Ni and Mo_xC nanoparticles, the optimized electrocatalyst displayed excellent catalytic activity with low overpotentials of 183 mV and 216 mV for the HER at the current density 10 mA cm⁻² in 1.0 M KOH and 0.5 M H₂SO₄ solution. The stability of the electrocatalyst could be well maintained for 24 h. These results indicate that the method to prepare hybrid (Ni-Mo_xC) is a simple way to produce cost-effective and high-efficient molybdenum carbide for hydrogen evolution.     

Adjusting electronic structure coupling of Fe–Ni2P (NiFeP-MOF) multilevel structure for ultra-activity and durable catalytic water oxidation

Efficient electrocatalyst for alkaline oxygen evolution reaction is the critical core to the wide application of metal-air energy storage and water electrolysis hydrogen energy. Therefore, appropriate design of highly active and stable non-noble metal oxygen evolution electrocatalyst with good electronic structure and multilevel structure is both a goal and a challenge. Here, we report a Fe–Ni₂P electrocatalyst (NiFeP-MOF) with multilevel structure, which was obtained by anion exchange on the basis of Fe–Ni(OH)₂ (NiFe-MOF) grown on nickel foam in situ by solvothermal method. As expected, Fe substitution regulates the Ni oxidation state in the NiFeP-MOF and realizes electronic structure coupling, showing a highly active and stable oxygen evolution reaction (OER) in alkaline electrolyte solution. Specifically, the NiFeP-MOF demonstrates an ultralow overpotentials (232 mV, 10 mA cm^?2; 267 mV 100 mA cm^?2), respectively, an extremely small Tafel slope (34 mV dec^?1). Separately, the electrocatalyst shows an excellent cycle stability at 10 mA cm^?2 for 12 h (43,200 s). More importantly, this work come up with an available policy for the preparation of excellent alkaline hydrolysis electrolysis catalysts and air cathodes with excellent performance.     

Ni activated Mo2C nanoparticles supported on stereotaxically-constructed graphene for efficient overall water splitting

Exploring cost-effective, high-efficiency and stable electrocatalysts for overall water splitting is greatly desirable and challenging for sustainable energy. Herein, a novel designed Ni activated molybdenum carbide nanoparticle loaded on stereotaxically-constructed graphene (SCG) using two steps facile strategy (hydrothermal and carbonization) as a bifunctional electrocatalyst for overall water splitting. The optimized Ni/Mo₂C(1:20)-SCG composites exhibit excellent performance with a low overpotential of 150 mV and 330 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively to obtain a current density of 10 mA cm^?2 in 1.0 M KOH solution. In addition, when the optimized Ni/Mo₂C(1:20)-SCG composite is used as a bifunctional electrode for overall water splitting, the electrochemical cell required a low cell voltage of 1.68 V at a current density of 10 mA cm^?2 and long-term stability of 24 h. More significantly, the synergetic effects between Ni-activated Mo₂C nanoparticles and SCG are regarded as a significant contributor to accelerate charge transfer and promote electrocatalytic performance in hybrid electrocatalysts. Our works introduce a novel approach to design advanced bifunctional electrodes for overall water splitting.     

A nano-spherical structure Ni3S2/Ni(OH)2 electrocatalyst prepared by one-step fast electrodeposition for efficient and durable water splitting

Developing non-noble metal catalysts with excellent electrocatalytic performance and stability is of great significance to hydrogen production by water electrolysis, but there are still problems of low activity, complex preparation and high cost. Herein, we fabricated a novel Ni₃S₂/Ni(OH)₂ dual-functional electrocatalyst by a one-step fast electrodeposition on nickel foam (NF). While maintaining the electrocatalytic performance of Ni₃S₂, the existence of heterostructure and Ni(OH)₂ co-catalyst function greatly improves the overall water splitting performance of Ni₃S₂/Ni(OH)₂–NF. Hence, It shows a low overpotential of 66 mV at 10 mA cm^?2 for HER and 249 mV at 20 mA cm^?2 for OER. The dual-functional electrocatalyst needs only 1.58 V at 20 mA cm^?2 when assembled two-electrode electrolytic cell. Impressively, the electrocatalyst also shows outstanding catalytic stability for about 800 h when 20 and 50 mA cm^?2 constant current was applied, respectively which demonstrates a potential electrocatalyst for overall water splitting.     

One-step synthesis of unique catalyst Ni9S8@C for excellent MOR performances

A novel Ni₉S₈/C electrocatalyst for methanol oxidation reaction (MOR) is synthesized by a simple, cost-effective and one-pot strategy. The electrocatalyst Ni₉S₈ composed of micro and nanoparticles encapsulated inside carbon layers serves as carbon-supporter and fast ion and electron mobilization through the Ni₉S₈/C support materials. The sizes of Ni₉S₈/C nanoparticles range from 2.4 to 7.99 nm, reveals large surface area availability with plenty of active sites for electro-oxidation of methanol. The oxidation performance of electrocatalyst is determined in different solution of methanol and alcohol at various scan rates. At a scan rate of 50 mV s⁻¹, the Ni₉S₈/C catalyst delivers total 52 mA cm⁻² current density for 1.75 V potential (vs RHE) for 1 M KOH and 0.5 M methanol. The electrocatalyst shows low Rct circle and linear chronoamperometric graph for 5000 s, which demonstrate the outstanding stability of the electrocatalyst for methanol electro-oxidation reaction.     

Electrodeposited graphene hybridized graphitic carbon nitride anchoring ultrafine palladium nanoparticles for remarkable methanol electrooxidation

Exploiting high performance electrocatalysts is crucial for the effective electrooxidation of methanol, although some barriers exist. Herein, we develop a hybrid support composed of graphitic carbon nitride (g-C₃N₄) and reduced graphene oxide (rGO) synergistically anchoring sufficient ultrafine palladium (Pd) nanoparticles via a simple one-step electrodeposition technique. The morphology and structure were characterized by scanning/transmission electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy, which confirmed that the Pd nanoparticles were massively and uniformly dispersed on the support of g-C₃N₄@rGO with a the average particle size of 5.87 nm, deriving from the nitrogen in g-C₃N₄ contributing to the electron transport highway on the rGO nanosheet layer surface. Furthermore, electrochemical results suggested that the Pd/g-C₃N₄@rGO showed a high electrocatalytic efficiency for methanol oxidation with a high current density reached 0.131 mA cm⁻². Based on a novel approach to the g-C₃N₄@rGO hybrid nanostructure, this work offers a promising method for the design and synthesis for the superior performance methanol electrocatalyst.     

High throughput preparation of Ni–Mo alloy thin films as efficient bifunctional electrocatalysts for water splitting

The synthesis of cost-effective and high-performance electrocatalysts for water splitting is the main challenge in electrochemical hydrogen production. In this study, we adopted a high throughput method to prepare bi-metallic catalysts for oxygen/hydrogen evolution reactions (OER/HER). A series of Ni–Mo alloy electrocatalysts with tunable compositions were prepared by a simple co-sputtering method. Due to the synergistic effect between Ni and Mo, the intrinsic electrocatalytic activity of the Ni–Mo alloy electrocatalysts is improved, resulting in excellent HER and OER performances. The Ni₉₀Mo₁₀ electrocatalyst shows the best HER performance, with an extremely low overpotential of 58 mV at 10 mA cm^?2, while the Ni₄₀Mo₆₀ electrocatalyst shows an overpotential of 258 mV at 10 mA cm^?2 in OER. More significantly, the assembled Ni₄₀Mo₆₀//Ni₉₀Mo₁₀ electrolyzer only needs a cell voltage of 1.57 V to reach 10 mA cm^?2 for overall water splitting.     

Tungsten(VI) oxide as a versatile support for Pd nanocatalysts for alkaline direct alcohol fuel cells

The instability of carbon support materials has motivated the development of metal oxides supports which are stable under the fuel cell environment. In this study, tungsten (VI) oxide (WO₃) is utilized as a secondary support and cocatalyst for the electrooxidation of methanol and ethanol. Functionalized carbon nanodots employed as primary supports were blended with WO₃ nanoparticles to form a composite support onto which Pd nanoparticles were deposited by a borohydride reduction method. The synthesized Pd/fCNDs-WO₃ electrocatalysts were characterized by Transmission Electron microscopy (TEM), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy. XRD results proved that incorporating WO₃ into Pd/fCNDs electrocatalyst shifts the Pd diffraction peaks to lower 2Ɵ value due to lattice relaxation. XPS results revealed that W exist in oxidised form and confirmed the strong interaction between the support material and the catalyst. The Pd/fCNDs-WO₃ electrocatalysts exhibited a remarkable catalytic activity towards methanol and ethanol oxidation. High current densities of 87.24 mA cm⁻² and 44.23 mA cm⁻² were obtained for ethanol and methanol oxidation, respectively, using a catalyst with 2.5% Pd loading. EIS, CA and stability tests revealed that the presence of WO₃ in Pd/fCNDs electrocatalyst improves the kinetics, tolerance to poisoning and long-term durability in alkaline conditions. This superior performance is attributed to the electronic coupling between Pd and WO₃ nanoparticles.     

Synthesis and characterization of transition metal mixed oxide doped graphene embedded durable electrocatalyst for hydrogen evolution reaction

A promising electrocatalyst containing variable percentage of V₂O₅–TiO₂ mixed oxide in graphene oxide support was prepared by embedding the catalyst on Cu substrate through facile electroless Ni–Co–P plating for hydrogen evolution reaction. The solvothermal decomposition method was opted for tuning the crystalline characteristics of prepared material. The optimized mixed oxide was well characterized, active sites centres were identified and explained by X-ray diffraction, high resolution tunnelling electron microscopy, scanning electron microscopy coupled with energy dispersive X-ray and X-ray photon spectroscopy analysis. The structural and electronic characteristics of material was done by fourier transform infrared spectroscopy and the electrochemical behaviour of the prepared material was evaluated by using Tafel plot, electrochemical impedance analysis, linear sweep voltammetry, open circuit analysis and chronoamperometry measurements. The results show the enhanced catalytic activity of Ni–Co–P than pure Ni–P plate, due to synergic effect. Moreover, the prepared mixed oxide incorporated Ni–Co–P plate has a high activity towards HER with low over potential of 101 mV, low Tafel slope of 36 mVdec^?1, high exchange current density of 9.90 × 10^?2 Acm^?2.     

Boosting the activity of FeOOH via integration of ZIF-12 and graphene to efficiently catalyze the oxygen evolution reaction

Transition metal oxyhydroxides have been used as promising electrocatalysts for water splitting however, their catalytic activity is restricted due to low surface area and poor conductivity. Herein, we report novel composite FeOOH@ZIF-12/graphene composite as electrocatalyst for water oxidation, whereby ZIF-12 provide extra surface for the FeOOH dispersion whilst graphene act as excellent electron mediator. The composite shows a low overpotential value of 291 mV to attain a current density of 10 mA cm^?2 and a low Tafel slope value of 78 mV dec^?1. The catalyst offers a maximum current density of 101 mA cm^?2, while it gives a turnover frequency (TOF) value of 0.031 s^?1 at an overpotential of 291 mV only. The excellent activity and remarkable stability of composite is attributed to highly conductive and porous support.     

Three-dimensional porous graphene supported Ni nanoparticles with enhanced catalytic performance for Methanol electrooxidation

Three-dimensional porous graphene (3D-G) is prepared by template-assembly method and employed as catalyst support for Ni nanoparticles for methanol electrooxidation. Morphology characterization confirm that Ni nanoparticles with sizes around 20 nm are uniformly scattered on the pore wall surface of the three-dimensional graphene without apparent agglomeration. Electrochemical measurements indicate that the Ni/3D-G processes higher electrocatalytic activity for methanol oxidation reaction than that of the Ni nanoparticles supported on two-dimensional graphene (Ni/2D-G) and Ni nanoparticles without graphene. The peak current density on Ni/3D-G is 64.6 mA cm^?2, which is 1.5 times higher than that on Ni/2D-G. The remarkable electrocatalytic performance of the Ni/3D-G catalyst are mainly derived from the 3D graphene. As a carrier for methanol oxidation, the 3D-G with abundant pore architecture not only hinder the agglomeration of Ni particles that is beneficial to accelerating the efficient charge transport through the whole catalyst, but also offer readily accessible channels for the diffusion of CH₃OH to the active sites of catalyst surface.     

Uniform cobalt nanoparticles embedded in nitrogen-doped graphene with abundant defects as high-performance bifunctional electrocatalyst in overall water splitting

Co nanoparticles with uniform size (about 5 nm) embedded in N-doped graphene (Co-NG) were explored in this work. The introduction of a second carbon source of citric acid during synthesis prevented the Co atoms from growing up, thus regulating the size of the cobalt nanoparticles. N atoms in N-doped graphene had more lone-pair electrons, making it easier to capture electrons from hydrated ions, and facilitating the dynamics procedure of HER. Furthermore, N dopant rendered larger positive charge density on the adjacent carbon atoms, which was conducive to OER and HER. At 10 mA cm^?2 of the current density, the Co-NG/CC catalyst's overvoltage of HER was 78 mV, approaching that of 20% Pt/C (59 mV), an efficient precious metal electrocatalyst for HER, while its overvoltage of OER was about 225 mV, 12.5% lower than that of RuO₂ (257 mV, a common precious metal oxide OER electrocatalyst). In addition, this Co-NG/CC composite bifunctional catalyst displayed good electrochemical stability in alkali solution and might be designed as a dual-function catalyst in the application of overall water splitting. The cell voltage of Co-NG/CC//Co-NG/CC was only 1.66 V, approaching to that of full precious metal cell of Pt/C//RuO₂ (1.52 V), and revealing the good commercial application prospects of this composite bifunctional catalyst.     

Top-down preparation of Ni–Pd–P@graphitic carbon core-shell nanostructure as a non-Pt catalyst for enhanced electrocatalytic reactions

Electrochemical reactions such as the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and methanol oxidation reaction (MOR) are essential for energy conversion applications such as water electrolysis and fuel cells. Furthermore, Pt or Ir-related materials have been extensively utilized as electrocatalysts for the OER, ORR, and MOR. To reduce the utilization of precious metals, innovative catalyst structures should be proposed. Herein, we report a bi-metallic phosphide (Ni₂P and PdP₂) structure surrounded by graphitic carbon (Ni–Pd–P/C) with an enhanced electrochemical activity as compared to conventional electrocatalysts. Despite the low Pd content of 3 at%, Ni–Pd–P/C exhibits a low overpotential of 330 mV at 10 mA cm^?2 in the OER, high specific activity (2.82 mA cm^?2 at 0.8 V) for the ORR, and a high current density of 1.101 A mg^?1 for the MOR. The superior electrochemical performance of Ni–Pd–P/C may be attributed to the synergistic effect of the bi-metallic phosphide structure and core-shell structure formed by graphitic carbon.     

A highly active composite electrocatalyst Ni–Fe–P–Nb2O5/NF for overall water splitting

This work demonstrates a facile Nb₂O₅-decorated electrocatalyst to prepare cost-effective Ni–Fe–P–Nb₂O₅/NF and compared HER & OER performance in alkaline media. The prepared electrocatalyst presented an outstanding electrocatalytic performance towards hydrogen evolution reaction, which required a quite low overpotential of 39.05 mV at the current density of ?10 mA cm^?2 in 1 M KOH electrolyte. Moreover, the Ni–Fe–P–Nb₂O₅/NF catalyst also has excellent oxygen evolution efficiency, which needs only 322 mV to reach the current density of 50 mA cm^?2. Furthermore, its electrocatalytic performance towards overall water splitting worked as both cathode and anode achieved a quite low potential of 1.56 V (10 mA cm^?2).     

Sm2O3 promoted Pd/rGO electrocatalyst for formic acid oxidation

Herein, we report the synthesis of Sm₂O₃ incorporated palladium based electrocatalyst, supported over reduced graphene oxide (rGO). Pd_xSm_y nanoparticles (20 wt %) are distributed over rGO surface by using sodium borohydride reduction technique. Different physicochemical analyses are used to characterize the Pd_xSm_y/rGO electro-catalysts (x = 2,4,6 and y = 8,6,4). The synthesized materials (Pd_xSm_y/rGOs) are investigated for their catalytic capabilities toward electro-oxidation of formic acid. The results show that adding Sm₂O₃ to the Pd/rGO electrocatalyst boosts electrochemical activities of the materials toward formic acid oxidation. The optimized catalyst (Pd₆Sm₄/rGO) shows excellent activity towards formic acid oxidation with current density of 46.70 mA/cm² compared to reference catalysts i.e., Pd/rGO (28.78 mA/cm²) and Pd/C (22.22 mA/cm²). The optimized catalyst also demonstrates high CO tolerance and great stability during formic acid oxidation reaction. The enhanced activity and stability are attributed to the synergistic interaction between Sm₂O_3, and palladium nanoparticles supported over reduced graphene oxide.     

Electrochemical conversion of CO2 to methanol using a glassy carbon electrode,modified by Pt@histamine-reduced graphene oxide

The electrochemical reduction of CO₂ to value-added products is one of the useful approaches to reducing the effects of global climate change. Herein, a novel electrocatalyst consisting of platinum nanoparticles on histamine-reduced graphene oxide plates (Pt@His-rGO) supported by a glassy carbon (GC) substrate for the electrochemical conversion of CO₂ to methanol has been developed. The nanocomposite was optimized in terms of pH, applied potential, CO₂ purging time and platinum loading for the highest current densities and faradaic efficiencies toward methanol production. The best results were obtained in a solution containing KNO₃ 0.1 mol L⁻¹ at the pH of 2.0, the applied potential of −0.3 V vs Ag/AgCl (KCl_sat), CO₂ purging duration of 30 min and Pt loading of 5.17 × 10⁻⁷ mol cm⁻². The faradaic efficiency of 37% was obtained for methanol production. The prepared nanocomposite requires a lower applied potential and serves as an intermediate stabilizer through the production of methanol.     

Highly dispersed MnO nanoparticles supported on N-doped rGO as an efficient oxygen reduction electrocatalyst via high-temperature pyrolysis

Transition metal-based compounds, due to their excellent ORR catalytic performance under alkaline condition, have recently emerged as one of the most promising alternatives to noble metal-based ORR catalysts. It is worth noting that manganese oxide can take an unique advantage for decomposition of intermediate adsorption products H₂O₂ and can effectively reduce O₂ to OH⁻. However, most research has focused on MnO₂, while attention has rarely been paid to MnO catalysts. In addition, under high-temperature pyrolysis condition, MnO is the most stable manganese oxide but MnO nanoparticles easily agglomerate. Hence, it is very difficult to obtain well-dispersed and small-sized MnO nanoparticles. Herein, on the basis of pre-synthesizing uniformly distributed manganese complexes on the reduced graphene oxide (rGO), we innovatively prepare highly dispersed and small-sized MnO nanoparticles (~3.94 nm) via high-temperature pyrolysis, which are uniformly anchored on N-doped reduced graphene oxide (NrGO) as an efficient oxygen reduction electrocatalyst. The as-obtained MnO/NrGO (1050 °C) electrocatalyst achieves satisfactory onset potential (0.942 V) and half-wave potential (0.820 V) under alkaline condition. And the limiting current density is 4.17 mA cm⁻², which is very close to that of Pt/C (20 wt%, JM). Meanwhile, MnO/NrGO (1050 °C) catalyst presents superior longstanding durability and methanol resistance than Pt/C (JM). This work indicates that high-temperature pyrolysis can improve the purity of manganese oxide, simultaneously the defects of NrGO can reduce particle size of MnO nanoparticles, which are greatly beneficial to improve ORR performance. This work provides a new idea for research of MnO catalysts for ORR in the future.