Self-supported Electrocatalysts Research Articles

Cathodic corrosion induced selective nano-crystallization of Nickel oxo/hydroxo complex on (NiFeCr)SiB amorphous ribbon for alkaline oxygen evolution reaction and methanol oxidation reaction

The study focuses on the development and optimization of (Ni87Fe4Cr9)78Si8B14 amorphous ribbons as self-supported electro-catalysts for oxygen evolution reaction (OER) and methanol oxidation reaction (MOR). Electro-catalytically active nano α-Ni(OH)2 phase (5–10nm) was generated in the amorphous ribbon surface through potentiostatic cathodic corrosion for different time intervals (0–120 min). The X-ray diffraction and scanning electron microscopy results shows the favourable occurrence of dense nanocrystallization of α-Ni(OH)2 between 45 and 90 min of corrosion time. For OER in 1 M KOH, the 60-min surface modified ribbon exhibits an overpotential of 295 mV at 10 mA/cm2 current density and tafel slope of 51 mV dec−1. In case of MOR in 1 M KOH +1 M MeOH, the 90-min corroded ribbon shows lowest potential of 1.38 V vs RHE, at 10 mA/cm2 and tafel slope of 34 mV dec−1. In addition to superior electro-catalytic activity, the optimal surface-modified ribbons show superior long-term stability for OER and MOR studies, indicating its potential application in hydrogen generation and direct methanol fuel cell.

Interface Engineering of Flower-like Co 2 P/WO 3-x /Carbon Cloth Catalysts with Oxygen Vacancies for Efficient Oxygen Evolution Reaction.

The Constructing an efficient and low-cost oxygen evolution reaction (OER) electrocatalyst is critical for improving the performance of electrolysis in alkaline water. In this study, a self-supported electrocatalyst of flower-like cobalt phosphide and tungsten oxide (Co2P/WO3-x/CC) was prepared on carbon cloth (CC)surface by hydrothermal reaction with solution immersion etching and phosphorization annealing under H2/Ar atmosphere. This strategy can generate oxygen vacancies (OV), improving the speed of charge transfer between cobalt phosphide (Co2P) and tungsten oxide (WO3-x) components. The catalyst greatly increases the electrochemical active surface area, which is beneficial for efficient oxygen evolution. Electrochemical testing studies show that in 1.0 M KOH solution, Co2P-WO3-x/CC catalyst exhibits good OER activity, with a low overpotential of 254 mV at 10 mA cm-2, a small Tafel slope of 58.32 mV dec-1. The synergistic effect of oxygen vacancies and Co2P with WO3-xcan regulate electronic structures, expose more active sites, and cooperatively enhancing the OER activity. This study provides a workable strategy for preparing efficient non-noble metal OER electrocatalysts on engineered interfaces and OV.

Electrospun Co-MoC Nanoparticles Embedded in Carbon Nanofibers for Highly Efficient pH-Universal Hydrogen Evolution Reaction and Alkaline Overall Water Splitting.

The construction of highly efficient and self-supported electrocatalysts with abundant active sites for pH-universal hydrogen evolution reaction (HER) and alkaline water splitting is significantly challenging. Herein, Co and MoC nanoparticles embedded in nitrogen-doped carbon nanofibers (Co-MoC/NCNFs) which display a bamboo-like morphology are prepared by electrospinning followed by the carbonization method. The electrospun MoC possesses an ultrasmall size (≈5nm) which can provide more active sites during electrocatalysis, while the introduction of Co greatly optimizes the electronic structure of MoC. Both endow the Co-MoC/NCNFs with superior HER performances over a wide pH range, with low overpotentials of 86, 116, and 145mV to achieve a current density of 10mAcm-2 in alkaline, acidic, and neutral media, respectively. Additionally, the catalyst exhibits remarkable alkaline oxygen evolution reaction (OER) activity with an overpotential of 254mV to reach 10mAcm-2. Density functional theory calculations confirm that electron transfer from Co to MoC regulates the adsorption free energy for hydrogen, thereby promoting HER. Moreover, an electrolyzer assembled with Co-MoC/NCNFs requires only a cell voltage of 1.59V at 10mAcm-2 in 1m KOH. This work opens new pathways for the design of high-efficiency electrocatalysts for energy conversion applications.

Bimetallic MOF derived Cu3P/Co2P grown on coal-based carbon fibers as self-supporting electrocatalyst for enhanced hydrogen evolution

Transition metal phosphides (TMPs) are often considered as a cost-effective replacement for precious metal catalysts in hydrogen evolution reaction (HER). Herein, the fibers are produced by combining coal with electrospinning technology, and then undergoing a pre-oxidation process for transforming into pre-oxidized coal-based fibers. Subsequently, CuCo-metal organic framework (CuCo-MOF) is grown on the pre-oxidized coal-based fibers using solvothermal method, and the Cu3P/Co2P/coal-based carbon fibers (Cu3P/Co2P/C-CFs) composite catalyst is successfully fabricated by phosphating at low temperature and carbonizing at high temperature. The uniformly grown nanoparticles (NPs) on the surface of C-CFs enhance the electrochemically active area, while the electron transfer between Cu3P and Co2P effectively modulates the electronic structure, increasing the catalytic activity of the catalyst for HER. In addition, the flexible C-CFs not only serve as self-supporting electrode but also effectively inhibit the agglomeration of Cu3P/Co2P NPs. Remarkably, the overpotential of Cu3P/Co2P/C-CFs is 83 mV at 10 mA cm−2 current density for HER in 0.5 mol L−1 H2SO4 solution. This study presents promising strategies for the high value-added utilization of coal and the synthesis of highly effective non-precious metal catalysts.

Arrayed metal phosphide heterostructure by Fe doping for robust overall water splitting

Transition metal phosphides (TMPs) show promise in water electrolysis due to their electronic structures, which activate hydrogen/oxygen reaction intermediates. However, TMPs face limitations in catalytic efficiency due to insufficient active sites, poor conductivity, and multiple intermediate steps in water electrolysis. Here, we synthesize a highly efficient bifunctional self-supported electrocatalyst, which consists of an N-doped carbon shell anchored on Fe-doped CoP/Co2P arrays on nickel foam (NC@Fe-CoxP/NF) using hydrothermal and phosphorization techniques. Experimental and theoretical results indicate that the modified morphology, with increased active site density and a tunable electronic structure induced by Fe doping in the CoP/Co2P heterostructure, leads to superior water electrolysis performance. The resulting NC@Fe0.1-CoP/Co2P/NF catalyst exhibits overpotentials of 122 mV for the hydrogen evolution reaction (HER) and 270 mV for the oxygen evolution reaction (OER) at 100 mA cm−2. Furthermore, using NC@Fe0.1-CoP/Co2P/NF as both the cathode and anode in an alkaline electrolyzer enables the cell system to achieve 100 mA cm−2 at a voltage of 1.70 V, while maintaining long-term catalytic durability. This work may pave the way for designing self-supported, highly efficient electrocatalysts for practical water electrolysis applications.

Upcycling Nickel Ions into self-supported Electrocatalyst by using ZIF-8/Bacterial cellulose adsorbent

Upcycling valuable metals from wastewater promises addressing the metal resource recycling and water pollution control issues simultaneously. In particular, upcycling Nickel (Ni) ions into electrocatalytic material has been proven a feasible route, but the current methods are still restricted by the complicated, environmentally-aggressive operation. Herein, we propose a low-cost, 3D-structured adsorbent, constructed by in-situ growing ZIF-8 on network-structured bacterial cellulose, for efficient Ni capture. It exhibits superior stability and 7.3-times higher Ni adsorption kinetics than the ZIF-8 alone. Importantly, the Ni-enriched adsorbent, after treatment of Ni-containing electroplating wastewater, could be pyrolytically converted into an efficient self-supported electrocatalyst for oxygen evolution reaction (OER), showing comparable OER activity to the state-of-the-art Ni-based electrode. This work provides a sustainable, facile route for Ni upcycling into self-supported electrode, which may be extended to recovery of various valuable metals from waste streams.

Surface Engineered Ni-Fe Foam As a Bi-Functional Electrode for Water Electrolysis in Alkaline Media

Using fossil fuels as a main source of energy has resulted in various environmentally hazardous effects, including global warming, climate change, and environmental pollution. Consequently, the development of a sustainable and clean source of energy became of urgent need. Water electrolysis has captured considerable attention as the main technology of hydrogen fuel production. It is particularly enticing due to its eco-friendliness and sustainability. Self-supported electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) have prominent roles in water electrolysis. Growing self-supported metal oxides, hydroxides1, phosphates2, sulfides3, etc. that possess high electrical conductivity, electrocatalytic activity, and structural stability have attracted attention lately. FeNi-based catalysts are considered one of the most promising electrocatalysts for water electrolysis in alkaline solutions. However, improving their catalytic activity and stability is one of the research targets before further practical applications. Nickel foam is widely used as a self-supported electrocatalyst due to its high surface area, low cost, and exceptional catalytic activity, with several studies focused on the deposition of nickel-iron materials on nickel foam for the development of a bifunctional catalyst for water electrolysis4. However, very few studies used NiFe mesh or foam to grow a self-supported catalyst material5.In this study, surface-engineered NiFe foam electrodes were developed by facile control of the Ni/Fe surface ratio via chemical leaching and oxidation with NaOH and NaClO4 followed by electrochemical activation, aiming to design a bifunctional electrocatalyst for both OER and HER. Results revealed that varying the ratios of NaOH and NaClO4 induced significant alterations to the surface composition (different Ni/Fe), and hence the active sites for OER and HER. The physicochemical and structural properties of the NiFe foam were characterized using glancing angle X-ray diffraction (GAXRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). Further, the catalytic activity of the modified electrode was assessed utilizing cyclic voltammetry, linear sweep voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy. References F. Dionigi and P. Strasser, Advanced Energy Materials, 6, 1600621 (2016).Y. Yu et al., Journal of Colloid and Interface Science, 607, 1091–1102 (2022).A. Shankar, R. Elakkiya, and G. Maduraiveeran, New J. Chem., 44, 5071–5078 (2020).H.-S. Hu, S. Si, R.-J. Liu, C.-B. Wang, and Y.-Y. Feng, International Journal of Energy Research, 44, 9222–9232 (2020).C. Sun et al., ACS Appl. Energy Mater., 4, 8791–8800 (2021).

Anchoring Ni(OH)2-CeOx Heterostructure on FeOOH-Modified Nickel-Mesh for Efficient Alkaline Water-Splitting Performance with Improved Stability under Quasi-Industrial Conditions.

Developing low-cost and industrially viable electrode materials for efficient water-splitting performance and constructing intrinsically active materials with abundant active sites is still challenging. In this study, a self-supported porous network Ni(OH)2-CeOx heterostructure layer on a FeOOH-modified Ni-mesh (NiCe/Fe@NM) electrode is successfully prepared by a facile, scalable two-electrode electrodeposition strategy for overall alkaline water splitting. The optimized NiCe0.05/Fe@NM catalyst reaches a current density of 100 mA cm-2 at an overpotential of 163 and 262mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, in 1.0m KOH with excellent stability. Additionally, NiCe0.05/Fe@NM demonstrates exceptional HER performance in alkaline seawater, requiring only 148mV overpotential at 100mA cm-2. Under real water splitting conditions, NiCe0.05/Fe@NM requires only 1.701V to achieve 100mA cm-2 with robust stability over 1000h in an alkaline medium. The remarkable water-splitting performance and stability of the NiCe0.05/Fe@NM catalyst result from a synergistic combination of factors, including well-optimized surface and electronic structures facilitated by an optimal Ce ratio, rapid reaction kinetics, a superhydrophilic/superaerophobic interface, and enhanced intrinsic catalytic activity. This study presents a simple two-electrode electrodeposition method for the scalable production of self-supported electrocatalysts, paving the way for their practical application in industrial water-splitting processes.

Combustion Growth of NiFe Layered Double Hydroxide for Efficient and Durable Oxygen Evolution Reaction.

NiFe layered double hydroxide (LDH) with abundant heterostructures represents a state-of-the-art electrocatalyst for the alkaline oxygen evolution reaction (OER). Herein, NiFe LDH/Fe2O3 nanosheet arrays have been fabricated by facile combustion of corrosion-engineered NiFe foam (NFF). The in situ grown, self-supported electrocatalyst exhibited a low overpotential of 248 mV for the OER at 50 mA cm-2, a small Tafel slope of 31 mV dec-1, and excellent durability over 100 h under the industrial benchmarking 500 mA cm-2 current density. A balanced Ni and Fe composition under optimal corrosion and combustion contributed to the desirable electrochemical properties. Comprehensive ex-situ analyses and operando characterizations including Fourier-transformed alternating current voltammetry (FTACV) and in situ Raman demonstrate the beneficial role of modulated interfacial electron transfer, dynamic atomic structural transformation to NiOOH, and the high-valence active metal sites. This study provides a low-cost and easy-to-expand way to synthesize efficient and durable electrocatalysts.

Prussian blue analogue-derived Co-Ni5P4 porous nanosheet arrays composite coal-based carbon nanofibers as efficient self-supported electrocatalyst for overall water splitting

The development of economical, earth-rich, and high-performance transition metal phosphides electrocatalysts is crucial for water splitting. Herein, the NiCo PBA/Ni(OH)2 hierarchical nanostructure arrays are in situ grown on the coal-based carbon nanofibers (C-CNFs) using hydrothermal and co-precipitation methods. Subsequently, the Co-doped Ni5P4 porous nanosheet arrays composite coal-based carbon nanofibers electrocatalyst (Co-Ni5P4@C-CNFs) is obtained through low-temperature phosphorization process. Benefiting from cation-doped, porous nanosheet arrays structure and self-supported conductive substrates, the Co-Ni5P4@C-CNFs has excellent electrocatalytic performance for overall water splitting. It provides low overpotentials of 75 mV for hydrogen evolution reaction (HER) and 231 mV for oxygen evolution reaction (OER) to achieve the current density of 10 mA cm−2 in 1 M KOH electrolyte. Furthermore, the Co-Ni5P4@C-CNFs demonstrates a low overall water splitting cell voltage of 1.537 V at current density of 10 mA cm−2 and remarkable long-term stability for over 160 h. It outperforms the most transition metal phosphide bifunctional electrocatalysts reported to date. This research provides a novel strategy for synthesizing high-performance transition metal phosphides bifunctional electrocatalysts.

Review—Self-Supporting Electrocatalysts for HER in Alkaline Water Electrolysis

Hydrogen is a prime candidate for replacing fossil fuels. Electrolyzing water to produce hydrogen stands out as a particularly clean method, garnering significant attention from researchers in recent years. Among the various techniques for electrolyzing water to produce hydrogen, alkaline electrolysis holds the most promise for large-scale industrialization. The key to advancing this technology lies in the development of durable and cost-effective electrocatalysts for the hydrogen evolution reaction (HER). Self-supporting electrode is an electrode structure in which a catalyst layer is formed directly on a substrate (such as carbon cloth, nickel foam, stainless steel, etc) without using a binder and with good structural stability. In contrast to traditional nanocatalysts, self-supporting electrocatalysts offer significant advantages, including reduced resistance, enhanced stability, and prolonged usability under high currents. This paper reviews recent advancements in HER electrochemical catalysts for alkaline water electrolysis, focusing on the utilization of hydrogen-evolving catalysts such as metal sulfides, phosphides, selenides, oxides, and hydroxides. With self-supported electrocatalysts as the focal point, the paper delves into progress made in their preparation techniques, structural design, understanding of reaction mechanisms, and strategies for performance enhancement. Ultimately, the future development direction of promoting hydrogen evolution by self-supported electrocatalysts in alkaline water electrolysis is summarized.

Interface coupling induced built-in electric fields accelerate electro-assisted uranium extraction over Co3O4@FeOx nanosheet arrays

Revealing the nature of enhanced electro-assisted uranium extraction activity by hetero-interface and M-O-H coordination bonds is an important and challenging task. Hence, Co3O4@FeOx nanosheet arrays with abundant M-O-H coordination bonds is fabricated as a binder-free and self-supporting electrocatalyst for electro-assisted uranium extraction from fluorine-containing uranium wastewater. As revealed by self-consistent energy band calculations and in-situ Kelvin Probe Force Microscopy (KPFM) analysis, the p-n heterojunction formed by Co3O4@FeOx provides a well-designed built-in electric field (BIEF), triggering the interfacial accumulation of uranium and accelerating the electro reduction kinetics of uranium. Consequently, Co3O4@FeOx shows remarkable U(VI) extraction ability (>95 %) in fluorine-containing uranium wastewater. By virtue of the XAFS spectra, free uranyl ions are captured by M-O-H on Co3O4@FeOx to form a sturdy 2 Oax-1 U-3 Oeq configuration, confirming the electrically driven separation of uranium and fluorine. Furthermore, DFT calculation indicates that the existent of M-O-H enhances the adsorption energy of uranium species, thus promoting uranium extraction efficiency.

Engineering of Self-Supported Electrocatalysts on a Three-Dimensional Nickel Foam Platform for Efficient Water Electrolysis

Engineering of Self-Supported Electrocatalysts on a Three-Dimensional Nickel Foam Platform for Efficient Water Electrolysis

NiCo-LDH coupled with 2D ZIF-derived Co nitrogen doped carbon nanosheet arrays as a self-supporting electrocatalyst for detection of formaldehyde.

Formaldehyde is susceptible to illegal addition to foodstuffs to extend their shelf life due to its antimicrobial, preservative and bleaching properties. In this study, a self-supporting "nanosheet on nanosheet" arrays electrocatalyst with core-shell heterostructure was prepared in situ by coupling NiCo layer double hydroxide with 2D ZIF derived Co-nitrogen-doped porous carbon on carbon cloth (Co-N/C@NiCo-LDH NSAs/CC). Co-N/C nanosheet arrays act as a scaffold core with good electrical conductivity, providing more NiCo-LDH nucleation sites to avoid NiCo-LDH agglomeration, thus having fast mass/charge transfer performance. While the NiCo-LDH nanosheet arrays shell with high specific surface area provide more active sites for electrochemical reactions. As an electrocatalytic sensing electrode, Co-N/C@NiCo-LDH NSAs/CC has a wide linear range of 1 μM to 13 mM for formaldehyde detection, and the detection limit is 82 nM. Besides, the sensor has been applied to the detection of formaldehyde in food samples with satisfactory results.

Exploring suitability of solid 3D substrates for designing self-supported electrocatalysts for water splitting.

The choice of solid 3D substrates to design electrocatalysts significantly impacts the efficiency and effectiveness of self-supported electrocatalysts used in water splitting. These substrates are pivotal in significantly boosting the performance by providing structural support, facilitating electron transport, and increasing the active surface area. This improvement leads to higher catalytic performance and better stability, ultimately optimizing the electrocatalytic process. The interaction between the substrate and the electrocatalyst can also affect the intrinsic properties of the catalyst, further influencing its performance. Therefore, understanding and optimizing the use of solid 3D substrates is vital for advancing water-splitting technologies. This article explores the critical role of solid 3D substrates in enhancing the activity of self-supported materials for water splitting. By examining recent developments and research in this region, we target to showcase a comprehensive understanding of how different 3D substrates influence electrocatalyst properties and performance and to highlight future directions for optimizing these systems in water-splitting applications.

Ce-doping induces rapid electron transfer in a bimetallic phosphide heterostructure to achieve efficient hydrogen production.

Using electrochemical water splitting to generate hydrogen is considered a desirable approach, which is greatly impeded by the sluggish dissociation of H2O and adsorption and desorption of H*. Effective hydrogen production can be achieved by speeding up the chemical process with a suitable electrocatalyst. In this work, we designed and synthesized a rare earth element cerium (Ce) regulated iron-nickel bimetallic phosphide Ce-NiFeP@NF (here NiFeP represents Fe2P/NiP2) nanoarray with nanoflowers. For the hydrogen evolution reaction (HER), Ce-NiFeP@NF only needs an overpotential of 106 mV to provide a current density of 10 mA cm-2, compared to NiFeP@NF (175 mV@10 mA cm-2). This self-supported electrocatalyst Ce-NiFeP@NF with a composite morphology exhibits excellent performance in the HER. Specifically, the introduction of Ce promotes the electron transfer process at the Fe2P/NiP2 heterojunction interface and the Ce-NiFeP@NF nanocomposite structure with nanoflowers has a larger electrochemically active specific surface area, which is more conducive to improving the intrinsic catalytic activity. Also, a dual-electrode alkaline electrolytic cell (Ce-NiFeP@NF functions as both the anode and the cathode) operates with a cell voltage of only 1.56 V to achieve a current density of 10 mA cm-2. The synergistic effect of rare earth element doping and heterojunction engineering can improve the morphology of intrinsic catalysts to achieve more efficient electrochemical water splitting for hydrogen production.

Metal-organic framework derived transition metal sulfides grown on carbon nanofibers as self-supported catalysts for hydrogen evolution reaction

Metal-organic framework (MOF) derived transition metal-based electrocatalysts have received great attention as substitutes for noble metal-based hydrogen evolution catalysts. However, the low conductivity and easy detachments from electrodes of raw MOF have seriously hindered their applications in hydrogen evolution reaction. Herein, we report the facile preparation of Co-NSC@CBC84, a porous carbon-based and self-supported catalyst containing Co9S8 active species, by pyrolysis and sulfidation of in-situ grown ZIF-67 on polydopamine-modified biomass bacterial cellulose (PDA/BC). As a binder-free and self-supported electrocatalyst, Co-NSC@CBC84 exhibits superior electrocatalytic properties to other reported cobalt-based sulfide catalytic materials and has good stability in 0.5 M H2SO4 electrolyte. At the current density of 10 mA cm−2, only an overpotential of 138 mV was required, corresponding to a Tafel slope of 123 mV dec−1, owing to the strong synergy effect between Co-NSC nanoparticles and CBC substrate. This work therefore provides a feasible approach to prepare self-supported transition metal sulfides as HER catalysts, which is helpful for the development of noble metal-free catalysts and biomass carbon materials.

Heterostructured MoO3 Anchored Defect-Rich NiFe-LDH/NF as a Robust Self-Supporting Electrocatalyst for Overall Water Splitting.

The rational design of inexpensive metal electrocatalysts with exciting catalytic activity for overall water splitting (OWS) remains a significant challenge. Heterostructures of NiFe layered double hydroxides (NiFe-LDHs) with abundant oxygen defects and tunable electronic properties have garnered considerable attention. Here, a self-supporting heterostructured catalyst (named MoO3/NiFe-NF) is synthesized via a hydrothermal method to grow NiFe-LDH with oxygen vacancies (OV) in situ on inexpensive nickel foam (NF). Subsequently, MoO3 is anchored and grown on the surface of NiFe-LDH by electrodeposition. The obtained catalysts achieved outstanding oxygen/hydrogen evolution reaction (OER/HER, 212mV/85mV@10mAcm-2) performance in 1mKOH. Additionally, when MoO3/NiFe-NF is utilized as the cathode and anode in OWS, a current density of 10mAcm-2 can be obtained as an ultralow battery voltage of 1.43V, a significantly lower value compared to the commercial electrolyzer incorporating Pt/C and IrO2 electrode materials. Finally, density functional theory (DFT) calculations and advanced spectroscopy technology are conducted to reveal the effects of heterojunctions and OV on the internal electronic structure of the electrical catalysts. Mainly, the present study provides a novel tactic for the rational design of remarkable, low-cost NiFe-LDH electrocatalysts with heterostructures for OWS.

Design of wood-based self-supporting metal catalyst based on NiCo2O4 bridge for efficient oxygen evolution

Design the ingenious structure of catalyst via a simple method is critical for reducing the overpotential of OER reaction. Herein, a wood-based self-supporting electrocatalyst with a three-dimensional layered structure was developed by coupling lignification-electro-deposition-carbonization process from wood substrate, NiCo2O4 and NiFe-LDH. Significantly, the layered porous structure of the wood substrate ensures the high efficiency of mass transfer and the stability of the catalyst. NiCo2O4 with array structure as a bridge connected effectively wood substrate and the metal active material, resulted in Ni-Fe metal regular growth on NiCo2O4 bridge. The obtained NiFe-LDH@NiCo2O4/CW exhibited a low overpotential of 82 mV, excellent long-term stability at 10 mA cm−2, high activity and stability. This work broadens a facile route for high value-added utilization of wood-based materials in oxygen evolution electrocatalysts.

Mechanically mixing copper and silver into self-supporting electrocatalyst for hydrogen evolution

Mechanically mixing copper and silver into self-supporting electrocatalyst for hydrogen evolution