Synthesis Of Electrocatalysts Research Articles

Surfactant-assisted fabrication of prussian blue analogs as bifunctional electrocatalysts for water and hydrazine oxidation

The development of multifunctional catalysts for sustainable and proficient utilization of chemical energy is the utmost demand of the time. Water and hydrazine are auspicious energy carriers because of their high hydrogen content and henceforth can be employed as chemical hydrogen storage materials or as fuels for the direct fuel cells. In the present study, cationic surfactant-assisted Prussian blue analogs (PBAs) i.e., Mx[Fe(CN)5(N2C6H4)]·yC19H34NBr abbreviated as SF[Fe-CNPy-M]; SF = N-tridecyl-3-methylpyridinium bromide and M = manganese (Mn), cobalt (Co) and nickel (Ni), are synthesized and utilized as bifunctional heterogeneous OER and HzOR electrocatalysts under mild reaction conditions. The synthesis of electrocatalysts is confirmed by spectroscopic techniques i.e., Fourier transforms infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX) analysis, and X-ray photoelectron spectroscopy (XPS). The electrochemical measurements reveal an increase in current density, electrochemical surface area and catalytic stability compared to the reported PBAs for OER and HzOR. Among all the synthesized PBAs, SF[Fe-CNPy-Co] displays better electrochemical activity towards OER with 101 mV·dec−1 Tafel slope and appreciably low overpotential value of 470 mV to attain the current density of 10 mA.cm−2. SF[Fe-CNPy-Co] is further tested for HzOR and the results show that it exhibits high activity with the diffusion coefficient of 3.55 × 10−6 cm2.s−1 and rate constant of 3.411× 10−4 cm.s−1. This work proposes a pristine pathway to formulate efficient bifunctional electrocatalysts employing surfactant-assisted pentacyanoferrates-based PBAs for OER and HzOR.

Synthesis of PtRe electrocatalysts supported on mesoporous carbon for the ethanol oxidation reaction

Mesoporous carbon was synthesized to be employed as support in PtRe anodic electrocatalysts. The catalysts were prepared by the polyol method with the following Re loadings: 1, 3, 5, and 10 wt.%. The N2 adsorption-desorption isotherms, thermogravimetric measurements, temperature programmed desorption and temperature programmed reduction of the support were performed and the catalysts were structurally characterized by temperature programmed reduction, H2 chemisorption, X-ray diffraction, X-ray photoelectron spectroscopy, benzene hydrogenation reaction, and transmission electron microscopy. Furthermore, the electrochemical characterization of the catalysts was carried out by cyclic voltammetry, chronoamperometry, and CO stripping techniques. The addition of Re leads to a decrease in the CO oxidation onset potential value. The PtRe(3)/MC catalyst exhibited the best electrocatalytic activity, showing an electrochemical active surface area value of 82.5 m2 gPt−1. Moreover, the potential and anodic current values for ethanol oxidation reaction were 889 mV vs Ag/AgCl and 648 mA mgPt−1, respectively. This result is consistent with electronic effects and the smallest particle size found for this catalyst.

Critical review on the development of biomass waste as precursor for carbon material as electrocatalysts for metal-air batteries

The latest and state-of-art research on biomass waste-derived carbon materials synthesized for air electrodes used in metal-air batteries were succinctly and comprehensively reviewed in this report. This report also aims to provide greater understanding as well as to identify the strength and challenges of metal-air batteries (MAB), biomass wastes as precursor and the synthesis steps of carbon materials from biomass wastes as well as to propose several research routes for the shortcomings of carbon material synthesis from biomass wastes. MAB is a promising energy storage technology, but its commercialization was hindered due to the absence of a stable and active bifunctional electrocatalyst as well as costly air cathode material. The air cathode which is the key component of MAB is desired to have bifunctional catalytic properties and hierarchical porous structure. Carbon materials were known to be able to perform as an electrode material while acting as a catalyst towards the charge-discharge reactions. Due to its abundance and renewability, biomass wastes have great potential as low-cost and sustainable precursors to synthesize carbon materials as the air cathode while achieving waste reduction. The synthesis of carbon electrocatalyst from biomass waste usually include but not limited to pretreatments, carbonization, activation and doping. The synthesis method controls the structure and size, as well as the elemental content of carbon particles. Activation and doping of heteroatoms or metals were proven to enhance the efficiency and stability of the synthesized carbon material. However, each biomass waste have unique properties which requires tailored synthesis method to obtain carbon material with desired properties. Information on the synthesis methods as well as other crucial information were reviewed in this work which can help to spur more research to promote the utilization of biomass waste materials in energy storage application and to accelerate the commercialization of MAB.

Low loading ORR selectivity evaluation of Pt-free catalysts with scanning electrochemical microscopy

The challenges associated to oxygen reduction reaction (ORR) electrocatalysis are undoubtedly the most intricate impediments to solve regarding fuel cell vehicle (FCV) commercialization, mainly due to the complexity of this reaction and the scarcity of the required electrocatalysts. The synthesis of non-precious electrocatalysts with high intrinsic selectivity is indeed crucial in this field, but the methodology utilized to come to selectivity conclusions is undeniably equally important. In this work, we demonstrate how the higher required electrode loadings of a Fe-N-MWCNT catalyst in a rotating ring disc electrode (RRDE) prevent access to all of the peroxide produced by the catalyst during ORR. Via a spraying technique, much smaller amounts of the same catalyst were deposited on a flat boron-doped diamond (BDD) and their loading was determined meticulously by atomic force microscopy (AFM). These ultra-low loadings were investigated using scanning electrochemical microscopy (SECM), which revealed higher peroxide production and lower selectivity. This finding may have crucial implications for future ORR investigations in the laboratory, considering the harmful effect peroxide has on the catalyst.

Pt-Te alloy nanowires towards formic acid electrooxidation reaction

The high-performance anodic electrocatalysts is pivotal for realizing the commercial application of the direct formic acid fuel cells. In this work, a simple polyethyleneimine-assisted galvanic replacement reaction is applied to synthesize the high-quality PtTe alloy nanowires (PtTe NW) by using Te NW as an efficient sacrificial template. The existence of Te atoms separates the continuous Pt atoms, triggering a direct reaction pathway of formic acid electrooxidation reaction (FAEOR) at PtTe NW. The one-dimensional architecture and highly active sites have enabled PtTe NW to reveal outstanding electrocatalytic activity towards FAEOR with the mass/specific activities of 1091.25 mA mg−1/45.34 A m−2 at 0.643 V potential, which are 44.72/23.16 and 20.26/11.75 times bigger than those of the commercial Pt and Pd nanoparticles, respectively. Density functional theory calculations reveal that Te atoms optimize the electronic structure of Pt atoms, which decreases the adsorption capacity of CO intermediate and simultaneously improves the durability of PtTe NW towards FAEOR. This work provides the valuable insights into the synthesis and design of efficient Pt-based alloy FAEOR electrocatalysts.

Study on synthesis and characterization of electrocatalyst containing platinum on graphite electrode for hydrogen evolution reaction

In this study, we have successfully synthesized electrode materials containing Pt on modified graphite by electrodeposition method, such as: Pt/C, Pt-Au/C Pt-Pd/C, Pt-Ni/C, Pt-Ni-Au/C, Pt-Ni-Pd/C. The formation of materials coating on the modified graphite surface is demonstrated through SEM, EDS results. Synthetic materials are used as catalysts for hydrogen evolution reaction (HER). The results show that Bimetallic composites containing Pt exhibit higher catalytic activity than the monometallic material Pt/C. Trimetallic materials Pt-Ni-Au/C and Pt-Ni-Pd/C have catalytic activity for HER insignificant lower than that of Pt-Au/C and Pt-Pd/C electrodes. However, the precious metal composition in the trimetallic composite material system is reduced, which is also an important goal of research and opens up prospects for the fabrication of next-generation composite materials systems.

Ordered macroporous carbonous skeletons implanted with dual-phase Co/CoFe nanoparticles for boosting electrocatalytic performance

The accessibility of active sites is crucial to electrochemical applications, therefore, rationally controlled synthesis of novel electrocatalysts with favorable mass transfer and active site exposure is imperative. In this work, ordered macroporous N-doped carbonous skeletons implanted with dual-phase Co/CoFe nanoparticles are successfully synthesized by directly pyrolyzing Fe3+-incorporated ZIF-67 (ZIF = zeolitic imidazolate framework), which are pre-synthesized by confined growth of Fe3+/ZIF-67 inside the ordered voids of well-assembled polystyrene template. The incorporated Fe species not only benefits the formation of dual-phase Co/CoFe active sites, but also activates the carbon skeletons by enhancing the content of pyridine-N. Benefiting from the favorable accessibility of these active sites caused by the macroporous structure, the Co/CoFe2.5@OMNC sample exhibits good performance toward oxygen reduction reaction (ORR) with four-electron transfer pathway. More importantly, the Co/CoFe2.5@OMNC sample retains the activity even after 10,000 sweeping cycles of durability test, which outperforms commercial Pt/C-20% and other samples.

Self-supporting ZnO-Cu2S nanoflower arrays heterostructure with superhydrophilic and aerophobic properties for oxygen evolution reaction

Oxygen evolution reaction (OER) is often considered as a major bottleneck in water splitting because of its slow kinetics and limited energy conversion efficiency. Herein, we constructed ZnO-Cu2S nanoflower arrays on copper foam (CF) substrate with porous structure and high conductivity for accelerated mass transfer and electron transfer. The ZnO-Cu2S heterostructure can generate a simple electron transport pathway, optimize the water adsorption energy, and thus improve the electrochemical performance. Meanwhile, superhydrophilic and aerophobic of ZnO-Cu2S/CF is conducive to the immersion of electrolyte, and the bubbles can be quickly detached from the electrode surface. As a result, the current density of ZnO-Cu2S/CF is 20 mA·cm−2, the potential is only 1.359 V, and it is stable for 24 h. The improvement of OER performance of electrocatalyst is mainly due to the increase of active sites, the acceleration of electron transfer between electrode and electrolyte, and the synergistic effect between ZnO and Cu2S. The design concept of ZnO-Cu2S/CF with aerophobic heterostructures provides new ideas for the design and synthesis of future electrocatalysts.

Palladium metallene confined on MXene with increased hydroxyl binding strength for highly efficient ethanol electrooxidation

Rational design and synthesis of high-performance electrocatalysts for ethanol oxidation reaction (EOR) is crucial to large-scale commercialization of direct ethanol fuel cells, but it is still an incredible challenge. Herein, a unique Pd metallene/Ti3C2Tx MXene (Pdene/Ti3C2Tx)-supported electrocatalyst is constructed via an in-situ growth approach for high-efficiency EOR. The resulting Pdene/Ti3C2Tx catalyst achieves an ultrahigh mass activity of 7.47 A mgPd-1 under alkaline condition, as well as high tolerance to CO poisoning. Insitu attenuated total reflection-infrared spectroscopy studies combined with density functional theory calculations reveal that the excellent EOR activity of Pdene/Ti3C2Tx catalyst is attributed to the unique and stable interfaces which reduce the reaction energy barrier of *CH3CO intermediate oxidation and facilitate oxidative removal of CO poisonous species by increasing the Pd-OH binding strength.

Rational design of PANI incorporated PEG capped CuO/TiO2 for electrocatalytic hydrogen evolution and supercapattery applications

Synthesis of efficient electrocatalysts for energy applications is a major area scientists are currently focusing on to address the twin challenges of energy shortfall and the production of clean energy. Herein, an efficient electrocatalyst, polyaniline incorporated with polyethylene glycol capped CuO/TiO2 is prepared, which is effective in hydrogen evolution reactions and energy storage applications. The characterizations like XPS, XRD, FT-IR, FE-SEM, HR-TEM, and BET have been carried out to confirm the successful formation of the synthesized PANI/CuO/TiO2 composite. At 10 mA/cm2 current density, the prepared composite exhibits a lesser overpotential of 536 mV and 1587.2 C/g at 1 A/g as the specific capacity. The electrode prepared using the PANI/CuO/TiO2 composite also shows cyclic stability up to 2000 cycles. The synthesized composite is an efficient electrocatalyst for energy related applications.

Assembly of NiFe-PBA nanoparticles on nanoflower-like NiFe-PBA@IF as enhanced oxygen evolution electrocatalyst at room temperature

Oxygen Evolution Reaction (OER) catalysts that overcome low energy barriers to improve the reaction efficiency of the OER are important for the development of future green energy sources. Herein, NiFe-PBA@IF layered nanoflowers were successfully prepared by etching iron foam (IF) using Prussian blue-like (PBA) material as a precursor. Notably, the fractured PBA nanosheets prepared by etching at room temperature had a suitable growth gradient and growth environment with the homogeneous nucleation environment, compared to the conventional method. In this environment, a layered NiFe-PBA structure can be formed on the surface of IF, enabling efficient green synthesis, reducing ecological and economic costs, and providing a clear source of catalytic activity. More importantly, NiFe-PBA@IF has a nanoparticle structure anchored on NiFe-PBA stacked nanoflowers, which can expand the surface roughness and electrochemical active area of the sample, so the OER performance in 1 M KOH is 253 mV@10 mA·cm−2. The green and direct synthesis of PBA electrocatalysts can provide new ideas for the efficient synthesis of other OER electrocatalysts at room temperature and will further provide an effective template for the industrial application of OER electrocatalysts.

Controllable synthesis of Co/MnO heterointerfaces embedded in graphitic carbon for rechargeable Zn–air battery

Owing to the unique geometric and electronic structure, design and synthesis of electrocatalysts with well defined heterointerfaces are essential for clean energy technologies, for instance water-splitting and Zn-air batteries. Herein, a bifunctional electrocatalyst assembled by Co/MnO nanoparticles and nitrogen doping double-sphere carbon (denoted as Co/MnO@N-DSC), was fabricated via a solvothermal and pyrolysis strategy. The Co/MnO@N-DSC catalysts exhibit an enhanced bifunctional oxygen electrocatalytic performance for Oxygen reduction reaction (ORR) (E1/2, 0.84 V vs. RHE) and oxygen evolution reaction (OER) (Eonset, 1.54 V vs. RHE). As an air cathode catalyst, the Co/MnO@N-DSC-based Zn-air battery can afford prime performance, over the commercial noble-metal-based Zn-air battery. Theoretical calculation results indicate that the synergism of Co (111)/MnO (200) heterointerfaces can enhance charge transfer and provide extra electrons for the reaction processes. This work provides a promising manoeuvre to uplift bifunctional catalytic activity by increasing the synergy from heterointerfaces of transition-metal/metal oxide in oxygen electrocatalysis.

Green fabrication of nanostructured Ni(OH)2/Ni/Carbon felt electrodes with water-containing deep eutectic solvent for enhanced water electrolysis performance

To produce green hydrogen, the development of high-performance, environmentally friendly, and cost-effective electrocatalysts for efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is imperative. This study explores the potential application of water-containing deep eutectic solvents (DESs) in the synthesis of nanostructured electrocatalysts for water electrolysis. Ni(OH)2/Ni/carbon felt (CF) composite electrodes are developed via one-step electrodeposition in a water-containing choline chloride/urea DES as a green reaction medium. Heterostructured Ni(OH)2/Ni nanosheets are formed and uniformly deposited on the CF substrate with the addition of 10 wt% water to DES (CU10W), which increases active sites for HER and OER. The initial confinement of water molecules by the DES is found to be crucial in forming the hierarchical structure of the electrocatalysts. Notably, the CU10W electrode exhibits excellent bifunctional activity toward HER and OER, with reduced overpotentials of 192 and 564 mV, respectively, at 100 mA cm−2. This renders the CU10W electrode-based electrolysis system stable with a reduced cell voltage of 1.69 V and a high Faradaic efficiency of over 99% for the HER. The augmented electrochemical active surface area and reduced charge transfer resistance of the CU10W electrode account for the improved HER/OER performance associated with the special hierarchical Ni(OH)2/Ni nanostructure.

Rapid synthesis of NiMo-based electrocatalysts at room temperature for efficient oxygen and hydrogen evolution in seawater

Rapid synthesis of NiMo-based electrocatalysts at room temperature for efficient oxygen and hydrogen evolution in seawater

Conductive Ytterbium Metal–Organic Framework Composite: A Lanthanide-Based Complex ORR Catalyst

Extensive research work has been invested in the past decade in finding replacements for platinum-based electrocatalysts for the oxygen reduction reaction in fuel cells. The majority of these alternative electrocatalysts are based on transition-metal ions coordinated by organic ligands. Different from previously reported approaches for electrocatalysts, we describe here the synthesis, characterization, and oxygen reduction reaction activity of lanthanide complex electrocatalyst with ytterbium as the metal center. A metal–organic framework of Yb and benzene tricarboxylic acid as a ligand was synthesized on activated carbon (Yb(III)BTC@AC) to achieve electrical conductivity in a procedure similar to M-BTC@AC electrocatalysts with transition-metal centers. The Yb complex in activated carbon presents oxygen reduction reaction activity in alkaline solution with high onset potential relative to other nonpyrolyzed molecular electrocatalysts and proceeds mostly through the preferred four-electron reduction mechanism. This work presents a novel category of platinum group metal-free electrocatalysts as an alternative electrocatalyst for the oxygen reduction reaction.

Surface Structure Engineering of Two‐Dimensional Ni(OH)2 with Enhanced Urea Oxidation Performance

AbstractWe herein report a facile two‐pot method to prepare a series of the two‐dimensional Ni(OH)2 nanocrystals with varied surface structures via the in‐situ surface transformation derived from Nickel metal‐organic framework (Ni‐MOF) in KOH solution at room temperature. The Ni(OH)2 obtained at the KOH concentration of 0.25 M displayed superior performance among the samples in terms of activities and stability. Further investigation proves that the enhanced urea oxidation reaction (UOR) activities can be ascribed to the cooperation of the larger electrochemical surface area, a faster electronic transfer speed, and a lower transfer resistance on the surface. These findings provide a new route for the rational design and synthesis of advanced electrocatalysts with relatively lower energy consumption that aims to be large‐scale synthesized and utilized in clean energy conversion and applications.

Mechanistic insight into hydrothermally prepared molybdenum-based electrocatalyst for overall water splitting

Electrochemical water splitting is a technology that is gaining traction in the quest for zero-carbon energy and has the potential to produce enough hydrogen to meet the world's growing demand for sustainable and clean energy. It is still essential to develop inexpensive catalysts to replace noble metals like platinum or ruthenium in large-scale hydrogen production. Molybdenum (Mo)-based electrocatalysts have become extremely popular because of their high activity and wide pH range stability. The hydrothermal method is widely used among different synthetic methods due to its environmental friendliness. In this review, we briefly discuss the mechanistic insight of hydrothermally prepared Mo-based electrocatalysts for overall water splitting application. First, we cover some essential concepts and important aspects of water splitting and then discuss the fundamental processes by which oxygen and hydrogen evolve. Finally, the mechanistic understanding of several Mo-based electrocatalysts (monometallic, bimetallic, trimetallic, etc.) for total water splitting has been summarized. Additionally, we highlight novel strategies and impending challenges in the design and synthesis of high-performance electrocatalysts.

Single Cu atoms confined in N-doped porous carbon networks by flash nanocomplexation as efficient trifunctional electrocatalysts for Zn-air batteries and water splitting

Constructing efficient trifunctional single-atom electrocatalysts is exceedingly alluring and challenging for enhancing the efficiency of water splitting and Zn-air batteries (ZABs). Herein, a novel N-doped porous carbon network (SC-CuSA-NC) catalyst with Cu single atoms is constructed via flash nanocomplexation (FNC) technology and a double-network gel-limiting strategy. The novelty of this method lies in the combination of physical confinement and chemical confinement by FNC, which enables uniform spatial isolation and atomic-level dispersion of Cu atoms in the hydrogel, effectively inhibits the migration of Cu during synthesis, and achieves accurate and controllable preparation of Cu single atoms catalyst. Benefiting from the highly active Cu–N4 sites and distinct interconnected three-dimensional porous carbon network, SC-CuSA-NC shows superior ORR/OER/HER performance. Significantly, the ZAB assembled by SC-CuSA-NC displays a high specific capacity (775.0 mAh g−1) and could effectively drive water splitting (1.58 V at 10 mA cm−2). This work expands the synthesis method of single-atom catalysts and provides a new approach for the accurate and controllable synthesis of electrocatalysts for water splitting and ZABs.

Cu nanoclusters activating ultrafine Fe3N nanoparticles via the Mott-Schottky effect for rechargeable zinc-air batteries

The rational design and synthesis of cost-effective bifunctional oxygen electrocatalysts is crucial for the large-scale commercial applications of rechargeable zinc-air batteries. In this work, the CuNCs/Fe3N-NPCF catalyst was constructed by anchoring the metallic Cu/Fe3N ensembles with different sizes onto N-doped porous carbon nanosheets. The Mott-Schottky heterostructure formed by Fe3N nanoparticles and its surrounding Cu clusters enabled spontaneous electron transfer, which speeded up the electron supply from active sites to various oxygen intermediates. The electrophilic region on Cu side and the nucleophilic region on Fe3N side improved the adsorption of O2 and OH-, respectively. The CuNCs/Fe3N-NPCF exhibited onset potential of 0.98 V and low Tafel slope of 59.30 mV dec−1 in ORR, and overpotential of 282 mV at 10 mA cm−2 current density in OER. The CuNCs/Fe3N-NPCF-based zinc-air battery displayed the excellent catalytic activity and durability. These findings provided the guides in developing the efficient and stable Mott-Schottky bifunctional oxygen electrocatalysts.

Bimetallic substrate induction synthesis of binder-free electrocatalysts for stable seawater oxidation at industrial current densities

Oxygen evolution reaction (OER) is a bottleneck half-reaction of water splitting due to its sluggish kinetics involving four-electron transfer process. Developing a facile strategy for synthesis of low-cost and highly efficient OER catalysts is crucial but still very challenging. Herein, a bimetallic substrate induction (BSI) strategy to integrally construct supported metal catalysts (SMCs) as binder-free electrode in one step is proposed. As-used NiFe foam (NFF) not only plays the roles of the metal source and the reducing agent for in-situ growth of NiFeOOH supported Ru nanoparticles, but also guarantees the strong interaction between the SMCs and NiFe substrate. Consequently, the self-supported Ru/NiFeOOH/NFF electrode exhibits extraordinary OER performance in both alkaline salty water and seawater electrolytes. It can achieve the industrial current density of 500 mA cm−2 in 1 M KOH and 1 M KOH seawater at overpotentials of 285 and 330 mV, respectively, together with robust durability for over 400 h under current density of 100 mA cm−2. The combined theoretical and experimental investigations reveal that the in-situ formed metal-supported interaction accounts for both the optimal electronic states and the chemical stability. Furthermore, this BSI strategy can be applied in natural seawater for the scalable preparation of SMCs, demonstrating the universal applicability of BSI strategy.