Electrocatalysts For Applications Research Articles

Self‐Supported Fe‐Based Nanostructured Electrocatalysts for Water Splitting and Selective Oxidation Reactions: Past, Present, and Future

AbstractElectrochemical water splitting plays a vital role in facilitating the transition towards a sustainable energy future by enabling renewable hydrogen (H2) production, energy storage, and emission‐free transportation. Developing earth‐abundant electrocatalysts with outstanding overall water‐splitting performance, excellent catalytic activity, and robust long‐term stability is highly important in the practical application of water electrolysis. Self‐supported electrocatalysts have emerged as the most appealing candidate for practical H2 production due to their increased active site loading, rapid mass and charge transfer, and strong interaction with the underneath conducting support. Additionally, these electrocatalysts also provide enhanced reaction kinetics and stability. Here, a comprehensive review of recent progress in developing self‐supported Fe‐based electrocatalysts for water splitting and selective oxidation reactions is presented with examples of oxyhydroxides, layered double hydroxides, oxides, chalcogenides, phosphides, nitrides, and other Fe‐containing electrocatalysts. A comprehensive historical development in the synthesis of self‐supported Fe‐based electrocatalysts is provided, with an emphasis on the various deposition methods and the choice of self‐supported conducting substrates considering large‐scale commercial applications. An overview of mechanistic understanding and approaches for enhanced H2 production are also presented. Finally, the challenges and opportunities associated with developing Fe‐based electrocatalysts for practical applications in water splitting and alternative oxidation reactions are discussed.

Ce Hydroxide-Interfaced NiFe Sulfide Electrocatalyst with Improved Performance for the Oxygen Evolution Reaction.

The development of electrochemically inexpensive, durable, and active electrocatalysts for the oxygen evolution reaction (OER) is attracting considerable attention. The heterogeneous interfacing might regulate the electronic structure and further improve the electrochemical activity. Herein, a Ce(OH)3 nanoparticle-interfaced Fe-doped nickel sulfide (Ce(OH)3@Fe-Ni3S2) electrocatalyst was prepared to improve the OER performance. The fabricated electrocatalyst displayed excellent intrinsic activity and long-term stability in 1 M KOH for the OER. The catalyst shows an ultralow overpotential of 195 mV at a current density of 10 mA cm-2 and a Tafel slope of 52 mV dec-1, which are remarkably smaller than those of the control samples. This excellent electrocatalytic activity is attributed to the incorporation of Ce(OH)3 nanoparticles on the surface of the Fe-Ni3S2 nanosheet, which increases the electrochemical activity and enlarges the active surface area of the catalyst. In comparison to previous nonprecious OER electrocatalysts, the prepared Ce(OH)3@Fe-Ni3S2 exhibits greater electrocatalytic activity and longer durability, allowing for the selection of new electrocatalysts for practical applications.

Effect of the calcination temperature on the characteristics of Ni/Fe-oxide electrocatalysts for application in anion exchange membrane electrolysers

Ni–Fe oxides were prepared by the oxalate pathway and heat-treated at three different temperatures. An outstanding performance was achieved in AEMWE by NiFeOx 450-anode-based MEA.

Construction of N-doped carbon frames anchored with Co single atoms and Co nanoparticles as robust electrocatalyst for hydrogen evolution in the entire pH range

The development of low-cost, efficient, and high atomic economy electrocatalysts for hydrogen evolution reaction (HER) in the entire pH range for sustainable hydrogen production is of great importance but still challenging. Herein, we synthesize a highly dispersed N-doped carbon frames (NCFs) anchored with Co single atoms (SAs) and Co nanoparticles (NPs) catalyst by a doping-adsorption-pyrolysis strategy for electrocatalytic hydrogen evolution. The Co SAs-Co NPs/NCFs catalyst exhibits an excellent HER activity with small overpotential, low Tafel slope, high turnover frequency as well as remarkable stability. It also exhibits a superior HER performance in the entire pH range. Combining with experimental and theoretical calculation, we find that Co SAs with Co-N3 coordination structure and Co NPs have a strong interaction for promoting synergistic HER electrocatalytic process. The H2O molecule is easily activated and dissociated on Co NPs, while the generated H* is easily adsorbed on Co SAs for HER, which makes the Co SAs-Co NPs/NCFs catalyst exhibit more suitable H adsorption strength and more conducive to the activation and dissociation of H2O molecules. This work not only proposes a novel idea for constructing coupling catalyst with atomic-level precision, but also provides strong reference for the development of high-efficiency HER electrocatalysts for practical application.

Recent developments on transition metal–based electrocatalysts for application in anion exchange membrane water electrolysis

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Self‐Supported Electrocatalysts for Practical Water Electrolysis

AbstractOver the years, significant advances have been made to boost the efficiency of water splitting by carefully designing economic electrocatalysts with augmented conductivity, more accessible active sites, and high intrinsic activity in laboratory test conditions. However, it remains a challenge to develop earth‐abundant catalysts that can satisfy the demands of practical water electrolysis, that is, outstanding all‐pH electrolyte capacity, direct seawater splitting ability, exceptional performance for overall water splitting, superior large‐current‐density activity, and robust long‐term durability. In this context, considering the features of increased active species loading, rapid charge, and mass transfer, a strong affinity between catalytic components and substrates, easily‐controlled wettability, as well as, enhanced bifunctional performance, the self‐supported electrocatalysts are presently projected to be the most suitable contenders for practical massive scale hydrogen generation. In this review, a comprehensive introduction to the design and fabrication of self‐supported electrocatalysts with an emphasis on the design of deposited nanostructured catalysts, the selection of self‐supported substrates, and various fabrication methods are provided. Thereafter, the recent development of promising self‐supported electrocatalysts for practical applications is reviewed from the aforementioned aspects. Finally, a brief conclusion is delivered and the challenges and perspectives relating to promotion of self‐supported electrocatalysts for sustainable large‐scale production of hydrogen are discussed.

Structure and Interface Modification of Carbon Dots for Electrochemical Energy Application.

Carbon dots (CDs) as new nanomaterials have attracted much attention in recent years due to their unique characteristics. Notably, structure and interface modification (carbon core, edge, defects, and functional groups) of CDs have been considered as valid methods to regulate their properties, which contain electron transfer effect, electrochemical activity, fluorescence luminescent, and so on. Additionally, CDs with ultrasmall size, excellent dispersibility, high specific surface area, and abundant functional groups can guarantee positive and extraordinary effects in electrical energy storage and conversion. Therefore, CDs are used to couple with other materials by constructing a special interface structure to enhance their properties. Here, diverse structural and interfacial modifications of CDs with various heteroatoms and synergy effects are systematically analyzed. And not only several main syntheses of CDs-based composites (CDs/X) are summarized but also the merit and demerit of CDs/X in electrical energy storage are discussed. Finally, the applications of CDs/X in energy storage devices (supercapacitors, batteries) and electrocatalysts for practical applications are discussed. This review mainly provides a comprehensive summary and future prospect for synthesis, modification, and electrochemical applications of CDs.

Fabrication of Three-Dimensional Porous Materials with NiO Nanowalls for Electrocatalytic Oxygen Evolution

Nanosheets are two-dimensional (2D) nanocrystals that exhibit superior electrochemical performance. However, nanosheets are typically stacked horizontally toward the current collector, leading to poor utilization of individual nanosheets. Although most studies have fabricated three-dimensional (3D) structures using nanosheets, the wall thickness was a few hundred nanometers, suggesting that hundreds of nanosheets were restacked along the wall. In this study, we demonstrated the fabrication of a 3D structure constructed by NiO nanowalls with a thickness of 2–3 nm (3D-NiO). The specific surface area of 3D-NiO was found to be 42 m2 g–1, which is 2.6 times larger than that of NiO nanoparticles. The specific capacity of 3D-NiO was 2.5 times higher than that of NiO nanoparticles and could be attributed to the large specific surface area because of the nature of the thin nanowalls. The O2-evolution reaction (OER) activity of 3D-NiO at 1.65 V vs RHE was sixfold greater than that of NiO nanoparticles. The enhanced OER activity of 3D-NiO could be attributed to both the large specific surface area and the fabrication of diffusion paths within the 3D structure. The OER activity of 3D-NiO after 500 cycles was four times higher than that of NiO nanoparticles. Our results show that the 3D structure fabricated with thin nanowalls is a promising porous material for capacitor electrodes and electrocatalysts for applications in electrolysis and fuel cells.

Porous cobalt carbonate hydroxide nanospheres towards oxygen evolution reaction

• CoCO 3 PNSs are synthesized a facile precipitation transformation method. • The big discrepancy is inherent driving force for the generation of CoCO 3 PNSs. • CoCO 3 PNSs are consisted of tiny subnanorods with ca. 50 nm length and 5 nm diameter. • CoCO 3 PNSs reveal excellent electrocatalytic activity and durability for OER. • CoCO 3 PNSs can transform into the mixture of Co(OH) 2 and CoOOH during OER. Cost-effective nonprecious metal nanostructures are considered as highly promising electrocatalysts towards oxygen evolution reaction (OER). Optimizing their morphologies is an efficient strategy to enhance the electroactivity and durability of various electrocatalysts for practical application. Herein, porous cobalt carbonate hydroxide nanospheres (CoCO 3 PNSs) are successfully synthesized by using calcium carbonate (CaCO 3 ) nanospheres as a reaction precursor and self-template via a facile precipitation transformation method. Mainly, the solubility constant [ K sp (CoCO 3 ) = 1.4 × 10 −13 ] of CoCO 3 is much lower than that [ K sp (CaCO 3 ) = 2.8 × 10 −9 ] of CaCO 3 , resulting in the successful transformation of CaCO 3 nanospheres to CoCO 3 PNSs. Physical characterizations reveal that CoCO 3 PNSs consist of many tiny subnanorods (length of 50 nm, diameter of 5 nm), which have a high surface area and abundant channels between subnanorods. Compared to irregular cobalt carbonate hydroxide nanoparticles, CoCO 3 PNSs reveal enhanced OER performance in KOH solution, including a low overpotential of 310 mV and a small Tafel slope of 56 mV dec −1 .

Al, Fe-codoped CoP nanoparticles anchored on reduced graphene oxide as bifunctional catalysts to enhance overall water splitting

Rational design of high-efficiency and low-cost catalysts for water splitting electrolysis plays an important role in clean energy conversion technology. Herein, density functional theory simulations indicate that the codoping of p-metal Al and d-metal Fe could reasonably regulate the electronic structure of CoP, resulting in an optimal H adsorption free energy. Based on this finding, we successfully prepared a bifunctional catalyst of Al, Fe-codoped CoP nanoparticles/reduced graphene oxide, which displays superior HER performance in a wide pH range and OER performance in the alkaline medium with high H2/O2 evolution rates and Faradaic efficiencies. For overall water splitting, such a catalyst exhibits excellent activity (a low cell voltage of 1.66 V at 10 mA cm−2) and durability. The strategy of synergistic modulation of electronic structure by introducing different-type dopants into a hybrid proposed in this work is beneficial for designing novel electrocatalysts for applications in energy-conversion devices.

Ni-BTC Derived Porous Ni/C/Graphene Composite for Highly Sensitive Non-enzymatic Electrochemical Glucose Detection

Electrochemical detection of glucose, including enzymatic and non-enzymatic detections, has gained widespread attention due to its rapid response, unparalleled sensitivity, and common applications in both biomedical and healthcare fields. Compared with enzymatic glucose detection, non-enzymatic detection has lower cost, better stability and simpler immobilization operation. However, due to relatively inert nature of glucose and prone-to-contaminant characteristic of solid electrodes, non-enzymatic glucose detection suffers from weak sensitivity and reproducibility. To address these problems, various transition metal-based materials and graphene-based materials have been explored to improve electrochemical responses to glucose.Herein, a highly sensitive non-enzymatic glucose detection electrocatalyst was synthesized by in-situ growing porous NiO nanoparticles derived from Ni-BTC (1,3,5-Benzenetricarboxylic acid) on graphene (NiO/G). By virtue of highly porous Ni-BTC as a precursor, the composite exhibited homogeneous metal distribution, massive exposure of active sites, and spatially ordered structure. The NiO/G demonstrated superior steadiness, electron transfer rate, excellent electrocatalytic activity towards glucose oxidation, and high sensitivity (1030 μA mM−1 cm−2) in alkaline media. Thus, the NiO/G can be utilized as electrocatalysts for applications in non-enzymatic glucose detection, and the preparation strategy can be used to synthesize other nano-composites with low cost, such as CuO/G and Co/G, for non-enzyme glucose sensors.

Ni-BTC Derived Porous Ni/C/Graphene Composite for Highly Sensitive Non-enzymatic Electrochemical Glucose Detection

Electrochemical detection of glucose, including enzymatic and non-enzymatic detections, has gained widespread attention in both biomedical and healthcare fields. Non-enzymatic detection has lower cost, better stability, and simpler immobilization operation, but it lacks sensitivity and reproducibility. Herein, a highly sensitive non-enzymatic glucose detection electrocatalyst is synthesized by in-situ compositing porous Ni/C nanoparticles with graphene (G). By using a highly porous precursor, the Ni/C/G composite exhibits massive exposure and homogeneous distribution of metal active sites and spatially sequential structure, and thereby the composite demonstrates improved steadiness, electron transfer rate, superior electrocatalytic activity towards glucose oxidation, such as a high sensitivity of 1030 μA mM−1 cm−2 in alkaline media. Therefore, the Ni/C/G can be utilized as electrocatalysts for applications in non-enzymatic glucose detection, and the preparation strategy can be further developed to synthesize other low-cost nanomaterials for non-enzyme glucose sensors.

An efficient pH-universal electrocatalyst for oxygen reduction: defect-rich graphitized carbon shell wrapped cobalt within hierarchical porous N-doped carbon aerogel

The design and facile synthesis of active, robust, cheap, and earth-abundant electrocatalysts to replace precious Pt catalysts is highly desirable for the cathodic oxygen reduction reaction (ORR) in fuel cells and rechargeable metal batteries. However, maximizing the catalytic activity and stability of the electrocatalysts in catalyzing ORR is significantly important but still remains challenge. To address this issue, we herein reported an effective strategy that fabricate the cobalt nanoparticles encapsulated with defect-rich graphitized carbon shell in the hierarchical porous N-doped carbon aerogel (Co/NCA), which can simultaneously enhance the electrochemical stability while boosting the electrocatalytic activity for ORR. The desirable combination of the Co nanoparticles encapsulated with defect-rich graphitic carbon shells coupling with Co−Nx sites, the large accessible surface-active sites, and the hierarchical porous structure give rise to the superior electrocatalytic activity and stability for ORR in wide pH range. As expect, the as-obtained catalyst exhibits high efficiency for ORR with an onset potential of 0.95 V (versus reversible hydrogen electrode, vs. RHE) and a half-wave potential of 0.83 V in 0.1 M KOH, comparable to the commercial Pt/C. Importantly, the catalyst also provides excellent ORR properties in acidic and neutral media with almost a 4e− pathway and superior durability and methanol tolerance, showing a potential as electrocatalysts for practical applications.

Preparation and Characterization of Stable and Active Pt@TiO2 Core–Shell Nanoparticles as Electrocatalyst for Application in PEMFCs

PEMFCs are an established viable sustainable source of energy, especially for key sectors such as transportation and stationary and portable plants. Pt is their best performing electrocatalyst. How...

Highly improved electrocatalytic activity of NiSx: Effects of Cr-doping and phase transition

Hydrogen evolution reaction (HER) is a vital step for electrochemical energy conversion technologies. However, developing cost-efficient electrocatalysts remains a huge challenge. Here, we report that Cr-doped NiSx (Cr-NiSx) in situ grown on Ni foam via a hydrothermal sulfurization reaction can be an ultra-highly efficient and low-cost electrocatalyst for HER in alkaline condition. We find that the Cr-doping can trigger the formation of NiS and NiS1.19, leading to the suppression of Ni3S2 in the nanostructure. We show that Cr-NiSx exhibits an excellent HER activity with an ultralow overpotential of 81 mV at 10 mA cm−2, better than those of most nickel sulfide catalysts, and good stability. Our combined experimental and computational study reveals that the excellent performance is contributed by: (1) stabilized NiSx phase, (2) strongly improved conductivity, (3) greatly enhanced active sites, and (4) reduced Gibbs free energy for hydrogen adsorption (ΔGH) due to the Cr-doping. We believe that this work provides a simple approach to design cost-effective and ultra-highly efficient HER electrocatalysts for practical applications.

Cuprum Metal-Organic-Framework and Polyacrylonitrile-Derived Cu-N-C Electrocatalyst for Application in Zinc-Air Batteries

Cu-N-C electrocatalyst was successfully prepared with Cu-BTC and polyacrylonitrile as templates by electrospinning and in-situ growth method. The effect of various [Formula: see text]-doped content on the electrochemical performance of the catalyst were investigated and the Cu-N-C-0.25 exhibited the best OER/ORR catalytic activities. When it was applied to the cathode of the zinc-air batteries, the power density of Cu-N-C-0.25 was 209.1[Formula: see text]mW[Formula: see text]cm[Formula: see text], which exceeded that of the commercial Pt/C[Formula: see text]IrO2 hybrid catalyst (157[Formula: see text]mW[Formula: see text]cm[Formula: see text]). The excellent electrochemical performance may be attributed to large number of active sites and high specific surface area on Cu-N-C electrocatalyst. It will be a promising alternative to precious metal catalysts containing Pt, Ir or Ru and their oxides.

Designing transition-metal-boride-based electrocatalysts for applications in electrochemical water splitting.

Investigating renewable and clean energy materials as alternatives to fossil fuels can be foreseen as a potential solution to the global problems of energy shortages and environmental pollution. Recently, transition metal boride (TMB)-based materials have emerged as the rising star as efficient electrocatalysts for hydrogen evolution reaction (HER) and/or oxygen evolution reaction (OER). In this review, an overview of the most recent developments in the use of TMB-based materials as electrocatalysts for HER/OER or overall water splitting has been presented. Initially, we provide a comprehensive introduction of the fundamentals of electrochemical water splitting. Then, the synthesis approaches of TMB materials are summarized and compared. Emphasis is put on the various strategies for further improving the electrocatalytic performance of TMBs. Finally, challenges and future perspectives for TMBs in water-splitting applications are proposed.

Test factors affecting the performance of zinc–air battery

Abstract Zinc–air batteries provide a great potential for future large-scale energy storage. We assess the test factors that mainly affect the measured power density of the zinc–air battery. By fitting the polarization curves of the zinc–air batteries, we reveal the effect of testing parameters (electrode distance, electrolyte concentration, and oxygen flux) and preparation of catalysts ink on the activation, ohm, and concentration polarizations of the zinc–air battery. Finally, recommendations on evaluating the potentials of non-noble-metal electrocatalysts for applications in zinc–air batteries were given.

Bifunctional NiCo2Se4 and CoNi2Se4 nanostructures: Efficient electrodes for battery-type supercapacitors and electrocatalysts for the oxygen evolution reaction

We report the fabrication of bimetallic NiCo2Se4 and CoNi2Se4 nanostructures on nickel-foam (Ni-foam) substrates via a potentiostatic-deposition method by adjusting the molar ratio of Ni and Co metals. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses show that burl-like clusters with characteristic fluffy NiCo2Se4 and flake-like CoNi2Se4 hierarchical structures were deposited on the Ni-foam substrates. When used as battery-type electrodes in supercapacitors, both NiCo2Se4 and CoNi2Se4 electrodes exhibited outstanding capacity and good electrochemical properties. The CoNi2Se4 electrode delivered excellent capacity and cycling stability (602Cg–1 at 1Ag–1 and 98.30% retention after 5000 cycles at 40Ag–1) when compared to the NiCo2Se4 electrode (353Cg–1 at 1Ag–1 and 96.83% retention after 5000 cycles at 40Ag–1). Furthermore, as-deposited NiCo2Se4 and CoNi2Se4 hierarchical structures were employed as efficient electrocatalysts for water oxidation in alkaline solutions. NiCo2Se4 and CoNi2Se4 electrocatalysts showed low overpotentials of 257 and 244mV in a 1.0M KOH aqueous solution, respectively. The electrocatalysts also exhibited prolonged stability (NiCo2Se4 and CoNi2Se4 maintained currents of 95.6% and 97.5%, respectively, over 10h), which makes them comparable to well-known Ni and Co-based catalysts. Collectively, the as-deposited NiCo2Se4 and CoNi2Se4 are the most efficient bifunctional electrodes and electrocatalysts for application in battery-type supercapacitors and the oxygen evolution reaction, respectively, and can potentially be applied for energy conversion and storage processes.

Investigating the Role of Ligand Electronics on Stabilizing Electrocatalytically Relevant Low-Valent Co(I) Intermediates.

Cobalt complexes have shown great promise as electrocatalysts in applications ranging from hydrogen evolution to C-H functionalization. However, the use of such complexes often requires polydentate, bulky ligands to stabilize the catalytically active Co(I) oxidation state from deleterious disproportionation reactions to enable the desired reactivity. Herein, we describe the use of bidentate electronically asymmetric ligands as an alternative approach to stabilizing transient Co(I) species. Using disproportionation rates of electrochemically generated Co(I) complexes as a model for stability, we measured the relative stability of complexes prepared with a series of N, N-bidentate ligands. While the stability of Co(I)Cl complexes demonstrates a correlation with experimentally measured thermodynamic properties, consistent with an outer-sphere electron transfer process, the set of ligated Co(I)Br complexes evaluated was found to be preferentially stabilized by electronically asymmetric ligands, demonstrating an alternative disproportionation mechanism. These results allow a greater understanding of the fundamental processes involved in the disproportionation of organometallic complexes and have allowed the identification of cobalt complexes that show promise for the development of novel electrocatalytic reactions.