Non-noble Metal Electrocatalysts Research Articles

Rare-earth metal multicomponent perovskite as a electrocatalyst for water splitting

It is urgent to exploit non-noble metal electrocatalysts for water splitting. Herein, the multicomponent perovskites containing rare-earth metals La and Y were synthesized. The as-synthesized La0.7Y0.3Co0.5Ni0.5O3 shows a low OER overpotential of 338 mV at 10 mA cm−2 and fast kinetics, which are superior to those of commercial RuO2. Moreover, the overall water splitting voltage of La0.7Y0.3Co0.5Ni0.5O3 is 1.63 V at 10 mA cm−2, which is slightly higher than that of a commercial RuO2//Pt/C system (1.60 V).

Different Growth Behavior of MOF-on-MOF Heterostructures to Enhance Oxygen Evolution.

The exploration of non-noble metal electrocatalysts with high catalytic activity and stability for oxygen evolution reaction (OER) has become particularly urgent. Here, FeNi-based Prussian blue analogues (PBAs) were obtained by adding different solvents, where PBA particles preferentially grew on the surface plane/edge of coordination polymer precursor (Ni-ABDC) with various polarities. This resulted in the formation of FeNi-PBA-plane/edge morphologies, respectively. Notably, on account of more exposed PBAs, FeNi nanoparticles were uniformly supported on the porous N-doped carbon nanomaterials. Among them, the calcined FeNi-NC-800 underwent an interesting pre-activation process and exhibited a low overpotential of 281 mV at 10 mA cm-2 and a small Tafel slope of 82 mV dec-1 in 1.0 m KOH. This bimetallic sample showed superior OER activity and stability in comparison with control materials, which could be attributed to its abundant FeNi nanoparticles, high nitrogen content, large specific surface area, and synergistic effects between Fe and Ni atoms. In addition, relevant theoretical calculation on the optimal catalyst, FeNi-NC-800, further demonstrated its efficient OER performance with effective Fe-doping in the Ni-based oxyhydroxides.

Graphene-templated growth of MoS2−Ni3S2 heterostructures as efficient electrocatalysts for overall water splitting

Due to the advantages of large specific surface area, high mass transfer efficiency and easy access to active sites, two dimensional (2D) nanomaterials provide a great opportunity for the construction of new versatile electrocatalysts with superior properties. Herein, a graphene-templated growth of MoS2-Ni3S2 heterostructure with porous structure is successfully prepared on the Ni foam (MoS2/Ni3S2@G/NF) by one pot hydrothermal method. The electronic structure and surface properties of 2D chalcogenides are modified by heterogeneous interface and component engineering, so as to prepare a high-performance transition metal composite catalytic electrode for electrochemical reaction. The optimized MoS2/Ni3S2 @G/NF shows excellent bifunctional activity and durability in alkaline medium. It only needs 53 mV and 265 mV overpotential to reach 10 mA cm−2 current density of HER and 20 mA cm−2 current density for OER, respectively. When the composite is used as an advanced electrocatalyst for water splitting, the 1.47 V voltage required to achieve a current density of 10 mA cm−2, which is better than the most non-noble metal electrocatalysts. The heterostructures between MoS2, Ni3S2 and graphene are conducive to the synchronous chemical adsorption of hydrogen and oxygen-containing intermediates, which can improve the catalytic activity of overall water splitting.

Facile synthesis of self-support vanadium-doped Ni2P nanosheet arrays for highly efficient overall water splitting

It is urgent to explore non-noble metal electrocatalysts with high efficiency and durability for oxygen evolution reaction (OER), which is key to a spectrum of sustainable energy technologies. The electronic regulation via foreign ion/atom doping presents a valid route to improve the intrinsic activity of earth-abundant electrocatalysts. In this research, a facile and cost-effective self-assembly strategy is developed to fabricate the vanadium-doped nickel phosphide electrocatalysts (V-Ni2P) with a three-dimensional nanosheets structure. Then the effect of initial vanadium concentration on the morphology and properties of the target catalyst is investigated. It is found that the V-Ni2P electrocatalyst obtained at the NH4VO3 concentration of 1 mg mL−1 only requires a low overpotential of 228 mV to afford an OER current density of 80 mA cm−2, with a Tafel slope of 76 mV dec–1 and excellent electrocatalytic stability. On the other hand, enhanced hydrogen evolution reaction (HER) performance can also be acquired based on this unique structure under alkaline conditions. Finally, a water electrolysis device is assembled using V-Ni2P as the cathode and anode materials. To afford a current density of 50 mA cm−2, this device only needs a small voltage of 1.65 V, suggesting the potential of V-Ni2P as a bifunctional electrocatalyst for overall water splitting. This study provides a reference for the preparation of a highly active electrocatalyst with controllable composition and microstructure.

Synergistic effect of bimetallic nitride micro-flower promotes highly efficient overall water splitting

Developing efficient, low-cost, high-active, and durable bifunctional non-noble metal electrocatalysts is an essential requirement for hydrolytic hydrogen production. In this work, a three-dimensional (3D) flower-like bimetallic nitride (Co2NiN) is synthesized on the flexible carbon cloth (CC) that increases the surface area and exposes more active sites. At the same time, the synergistic effect between Ni3N, CoN and Co increases the electron transfer rate and optimizes the binding energy of intermediate products. The Co2NiN/CC electrode is superhydrophilic and superaerophobic, which guarantees intimate contact with the electrolyte and promotes timely the bubble release from the electrode, ensuring a high efficiency and stable working state. Therefore, the Co2NiN/CC electrode exhibits excellent catalytic performance for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media. Low overpotentials of only 123 mV and 315 mV are required to achieve the current densities of 10 mA·cm−2 and 20 mA·cm−2 for HER and OER, respectively. For overall water splitting, Co2NiN/CC as both anode and cathode require only 1.457 V for 10 mA·cm−2. This work shows the feasibility and potential of fabricating bimetallic nitrides electrocatalysts.

Inter-Electronic Interaction between Ni and Mo in Electrodeposited Ni-Mo-P on 3D Copper Foam Enables Hydrogen Evolution Reaction at Low Overpotential.

Electrocatalytic hydrogen evolution reaction (HER) via water electrolysis has been considered the most effective and sustainable route to produce clean hydrogen. Designing and structure optimization are the two important parameters to develop an affordable, easy to fabricate, and stable non-noble metal electrocatalyst for the production of hydrogen as a clean, sustainable, and green fuel. Herein, we have synthesized Ni-Mo-P on copper foam (Cuf) via a facile single-step electrodeposition method, which can show stratospheric efficiency toward HER with a Tafel slope of 67 mV dec-1 and a very low overpotential of only 53 mV at a current density of 20 mA cm-2. Cuf acts as a conducting substrate support and the existence of the inter-electronic effect between Ni and Mo results in substantial catalytic activity toward hydrogen generation. In addition to this, the catalyst shows long time stability of around 97.5 h with almost negligible degradation under the applied overpotential for HER in alkaline media. This work features the significance of structure design and construction of non-noble metal catalysts via a simple method for efficient hydrogen generation.

Bio-inspired micro-reactor mimicking multi-ridged mitochondrial intimae for efficient oxygen reduction

Fe3C embedded N-doped hollow rGO carbon spheres (Fe/N-HRCS) with multi-layered porous multi-ridged structure have been constructed as micro-reactors mimicking mitochondrial intimae. It is the first report on the application of a multi-layered porous hollow multi-ridged structure in oxygen reduction reaction (ORR) catalysis. Notably, the content of sacrificial template, silica nanoparticles, plays a decisive role on the microscopic morphology of micro-reactors. The optimal electrocatalyst, Fe/N-HRCS-1, exhibits a remarkable catalytic performance toward ORR with the onset potential of 1.03 V and half-wave potential of 0.88 V, which are comparable to that of commercial Pt/C. Such an extraordinary activity can be attributed to the synergistic effect between Fe3C nanoparticles embedded N-doped rGO layers and the distinctive bio-inspired structure. Moreover, the Fe/N-HRCS-1 catalyst also possesses superior methanol tolerance and durability, and thus holds a good promise for practical application. This work demonstrates a good example to design nature-inspired structures for high-efficiency non-noble metal electrocatalysts.

Dual-purpose nickel-iron layered double hydroxides by controlled lanthanide and phosphide incorporation for promoting overall water splitting efficiency

Developing non-noble metal and binder-free bifunctional electrocatalysts is of paramount importance but challenging for simultaneously promoting oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) processes. In the work, we introduce the dual-purpose utilization of nickel-iron layered double hydroxides (LDH) by a lanthanide and phosphide incorporation strategy for highly efficient overall water splitting (OWS). The screening of lanthanides effect shows that the lanthanide dopants (Ce, La and Nd) greatly contribute to the layer lattice distortion of LDH host structure and strong electronic interaction with Fe2+ species, leading to the increment of OER active species content of α-Ni(OH)2 phase and Fe3+. Specially, the formation of Ce3+/4+ reversible redox species can significantly promote charge transfer efficiency, thus corporately attributing to the excellent OER activity (η10 = 207 mV) and durability (300 mA·cm−2 for 200 h). On the other hand, we found that with further phosphide anions engineering, the HER Volmer step is accelerated in lanthanide and phosphide co-doped LDH, as compared to the solely phosphide doped LDH. The present of co-doped lanthanide can modify the adsorption energy of hydrogen intermediates and the Ce3+/4+ reversible redox species also facilitate the formation of HER active Ni2P phase, resulting in the lowest η10 value of 134 mV. The dual-purpose configuration of the Ce LDH // Ce LDH-P electrodes, provides low OWS potentials of 1.638 and 1.839 V to reach current densities of 10 and 100 mA·cm−2, respectively. These findings could introduce a new way to integrate nonprecious-metal bifunctional electrocatalysts into an efficient OWS system.

High-Performance Ternary NiCoMo Electrocatalyst with Three-Dimensional Nanosheets Array Structure.

Oxygen evolution reaction is a key process in hydrogen production from water splitting. The development of non-noble metal electrode materials with high efficiency and low cost has become the key factor for large-scale hydrogen production. Binary NiCo-layered double hydroxide (LDH) has been used as a non-noble metal electrocatalyst for OER, but its overpotential is still large. The microstructure of the catalyst is tuned by doping Mo ions into the NiCo-LDH/NF nanowires to form ternary NiCoMo-LDH/NF nanosheet catalysts for the purpose of enhancing the active sites and reducing the initial overpotential. Only 1.5 V (vs. reversible hydrogen electrode (RHE), ≈270 mV overpotential) is required to achieve a catalytic current density of 10 mA cm-2 and a small Tafel slope of 81.46 mV dec-1 in 1 M KOH solution, which manifests the best performance of NiCo-based catalysts reported up to now. Electrochemical analysis and micro-morphology show that the high catalytic activity of NiCoMo-LDH/NF is attributable to the change of the microstructure. The interconnected nanosheet arrays have the obvious advantages of electrolyte diffusion and ion migration. Thus, the active sites of catalysts are significantly increased, which facilitates the adsorption and desorption of intermediates. We conclude that NiCoMo-LDH/NF is a promising electrode material for its low cost and excellent electrocatalytic properties.

Interface engineering of Ni/NiO heterostructures with abundant catalytic active sites for enhanced methanol oxidation electrocatalysis

Designing efficient and stable non-noble metal electrocatalysts with good performance in reaction kinetics is desirable yet challenging for the study of methanol oxidation reaction (MOR). Herein, we have reported well-defined nanoscale nickel/nickel oxide (Ni/NiO) heterostructures supported by a three-dimensional (3D) porous graphene network (RG) via a delicate interface engineering technique. The as-prepared 3D Ni/NiO/RG composites achieve outstanding catalytic activity (79.5 mA cm−2/1262.1 mA mg−1) for MOR in alkaline solution, outperforming most reported non-precious catalysts. A combined experimental and computational investigation shows that such a good performance benefits from the specific Ni/NiO interface, which not only bears abundant accessible active sites but also improves the energetics of MOR. Moreover, this interface contributes to favorable kinetic and improved structural stability during electrocatalysis, ensuring superior catalytic performance after 1000 consecutive cyclic voltammetry tests for MOR. Our work demonstrates the potential of interface engineering in the rational design of efficient precious-metal-free electrocatalysts.

High-valence metal doped Co2FeAl alloy as efficient noble-metal-free electrocatalyst for alkaline hydrogen evolution reaction

Most efficient electrochemical hydrogen evolution reaction (HER) catalysts in alkaline solutions are based on precious metals, whose rarity and high cost are severely limiting their large-scale applications. In this work, we synthesized Mo-doped and W-doped Co2FeAl alloys by a simple coprecipitation method. The HER in alkaline solution is promoted through the synergistic effect of thermal annealing and doping of high-valence metal atoms. Thermal annealing could optimize the surface morphology and improve the crystallinity. In the meantime, the doping of high-valence metal atoms could further regulate the crystal structure and electronic structure of alloys. Therefore, annealing temperatures and doping concentrations have a marked impact on the catalytic performance. In particular, when the Mo doping concentration is 27 at% and the annealing temperature is 750 ℃, the synthesized Co2FeAlMo1.5 (750 ℃) alloy electrocatalyst exhibits the superior HER performance in alkaline media. It displays a low overpotential of only 71 mV at 10 mA cm−2 and a Tafel slope of 110 mV dec−1. An excellent stability is also demonstrated that the electrocatalyst can work stably for 20 h and the overpotential is only shifted by 2 mV after 1000 cycles. A series of characterization tests indicate that the crystal structure and electronic structure of Co2FeAlMo1.5 (750 ℃) are optimized, which can improve the catalytic activity and promote alkaline HER. This work provides a new strategy for improving the catalytic performance of non-noble metal electrocatalysts for alkaline HER.

Steady State Performance Evaluation of Noble-Metal Free Bifunctional Electrode for Overall Water Splitting

The emerging need of clean and renewable energy drives the exploration of effective strategies to produce molecular hydrogen. With the assistance of highly active non-noble metal electrocatalysts, electrolysis of water is becoming a promising candidate to generate pure hydrogen with low cost and high efficiency. This reaction takes place almost exclusively on Pt/C catalysts at the cathode which is expensive and need to be replaced by a metal-based catalyst that is cost effective and can show a comparable HER (Hydrogen Evolution Reaction) activity. Transition metal oxides, nitrides and sulfides have been widely explored as catalysts for HER and OER (Oxygen Evolution Reaction) due to their good electronic conductivity, stable and variable oxidation states, and superior corrosion resistance. In this research, MoNi4 embedded MoO3 nanorods are synthesized using facile hydrothermal method. Further, Molybdenum Vanadium Nitride is coated on top the synthesized electrode using RF/DC magnetron co-sputtering. This combination of hydrothermal and magnetron sputtering fabrication methods of the electrodes results in high surface area of the electrodes thereby improving the reaction kinetics of hydrogen production. The performance of the electrodes is tested in N2/O2 saturated 1M KOH solution using steady state technique called Staircase Voltammetry (SCV) instead of conventional dynamic LSV (Linear Sweep Voltammetry)/CV (Cyclic Voltammetry). This alternative method for testing is performed due to the exaggeration of the catalytic performance through conventional LSV/CV arising from double layer charging for nanostructured electrode. The electrodes are characterized by X-ray diffraction and SEM for structural and morphological analysis. Hence, we report the synthesis of novel MoVN on MoNi4/MoO2 nanorods using DC/RF Magnetron co-sputtering as an efficient, bifunctional, binder free electrode for overall water splitting. The electrode is characterised for both full-cell and half-cell configurations proving its stability for 12 hours. This work provides a reliable approach to the production of low cost and high-effectiveness electrodes for the application in commercial electrolyzers.

Engineering Transition Metals As Noble-Metal Free Bifunctional Electrode for Overall Water Splitting

The emerging need of clean and renewable energy drives the exploration of effective strategies to produce molecular hydrogen. With the assistance of highly active non-noble metal electrocatalysts, electrolysis of water is becoming a promising candidate to generate pure hydrogen with low cost and high efficiency.[1] This reaction takes place almost exclusively on Pt/C catalysts at the cathode which is expensive and need to be replaced by a metal-based catalyst which can show a comparable HER (Hydrogen evolution reaction) activity. Transition metal oxides, nitrides and sulfides have been widely explored as catalysts for HER and OER (Oxygen evolution reaction) due to their good electronic conductivity, stable and variable oxidation states, and superior corrosion resistance.[2] In this research, MoNi4 embedded MoO3 nanorods are synthesized using facile hydrothermal method. Further, Molybdenum Vanadium Nitride is coated on top the synthesized electrode using RF/DC magnetron co-sputtering.[3] This combination of hydrothermal and magnetron sputtering fabrication methods of the electrodes results in high surface area of the electrodes thereby improving the reaction kinetics of hydrogen production. The performance of the electrodes is tested in N2/O2 saturated 1M KOH solution using steady state technique called Staircase Voltammetry (SCV) instead of conventional dynamic LSV (Linear sweep voltammetry)/CV (Cyclic Voltammetry).[4] This alternative method for testing is performed due to the exaggeration of the catalytic performance through conventional LSV/CV arising from double layer charging for nanostructured electrode. The electrodes are characterized by X-ray diffraction and SEM for structural and morphological analysis. Hence, we report the synthesis of novel MoVN on MoNi4/MoO2 nanorods using DC/RF Magnetron co-sputtering as an efficient, bifunctional, binder free electrode for overall water splitting. The electrode is characterised for both full-cell and half-cell configurations proving its stability for 12 hours. This work provides a reliable approach to the production of low cost and high-effectiveness electrodes for the application in commercial electrolyzers.[1] J. Zhang et al., “Efficient hydrogen production on MoNi4 electrocatalysts with fast water dissociation kinetics,” Nat. Commun., vol. 8, no. May, pp. 1–8, 2017, doi: 10.1038/ncomms15437.[2] L. A. Santillán-Vallejo et al., “Supported (NiMo,CoMo)-carbide, -nitride phases: Effect of atomic ratios and phosphorus concentration on the HDS of thiophene and dibenzothiophene,” Catal. Today, vol. 109, no. 1–4, pp. 33–41, 2005, doi: 10.1016/j.cattod.2005.08.022.[3] B. Wei et al., “Bimetallic vanadium-molybdenum nitrides using magnetron co-sputtering as alkaline hydrogen evolution catalyst,” Electrochemistry Communications, vol. 93. pp. 166–170, 2018, doi: 10.1016/j.elecom.2018.07.012.[4] S. Anantharaj and S. Kundu, “Do the Evaluation Parameters Reflect Intrinsic Activity of Electrocatalysts in Electrochemical Water Splitting?,” ACS Energy Lett., vol. 4, no. 6, pp. 1260–1264, 2019, doi: 10.1021/acsenergylett.9b00686. Figure 1

Ni-B-Co nanoparticles based on ZIF-67 as efficient electrocatalyst for oxygen evolution reaction

• The excellent ZIF@Ni-B-Co catalyst was prepared via two-step static precipitation method at room temperature without any energy loss. • ZIF-67 as a precursor is beneficial to increase the specific surface area of the ZIF@Ni-B-Co catalyst, which facilitates exposure of active sites and electron transfer during OER. • The co-catalytic effect between Ni-B-Co nanoparticles and ZIF-67 support in ZIF@Ni-B-Co synergistically enhances OER performance. Exploiting efficient and earth-abundant non-noble metal electrocatalysts for oxygen evolution reaction (OER) is extremely important for energy conversion and storage infrastructure. Herein, we synthesized a Co-based zeolite imidazolate framework-derived bimetallic boride electrocatalyst by a facile method without any energy loss, named ZIF@Ni-B-Co, which exhibits excellent OER activity and stability. At the current density of 10 mA cm −2 , it has a low overpotential of 300 mV and a Tafel slope of 77 mV dec −1 , which is better than noble metal RuO 2 . The superior OER performance is attributed to the formation of a metal-boron bond, the morphology of specific dodecahedron, the large surface area and the fast charge transfer rate for the ZIF@Ni-B-Co catalyst. This work will provide new clues for the design and fabrication of metal-organic framework-derived composites, and offer some insights into the construction of crystallinity engineering.

Plasma-modified iron-doped Ni3S2 nanosheet arrays as efficient electrocatalysts for hydrogen evolution reaction

The development of efficient transition-metal catalysts for the hydrogen evolution reaction is significant to meeting global energy demands. In this study, to realize a high-performance electrocatalyst, we synthesize an Fe-doped Ni3S2 nanosheet material in situ on 3D structured nickel foam via the hydrothermal sulfide method, and then modify it by the dielectric barrier discharge plasma technique. Combining Fe atom doping and plasma modification increases the electrochemical surface area, provides an abundance of active sites, optimizes the electronic structure, and accelerates the reaction kinetics, thereby improving catalytic activity. As a result, the PA@Fe1/4-Ni3S2/NF catalyst exhibits excellent hydrogen evolution reaction activity, only requires ultra-low overpotentials to achieve a current density of 10 mA cm−2, and exhibits excellent durability. This study proposes a novel method for rationally designing non-noble metal electrocatalysts.

P-doped MoS2/CoxSy heterojunction for high-efficiency electrocatalytic hydrogen evolution performance in both acidic and alkaline electrolytes

It is still challenging for the development of highly efficient non-noble metal electrocatalysts toward hydrogen evolution reaction (HER). Herein, an unreported material constructing strategy of combining crystalline-amorphous hetero-interface and heteroatomic doping towards electrocatalytic HER is firstly presented. The authors fabricate a self-supported P-MoS2/CoxSy@C/CFP electrode consisting of P-doped crystalline-amorphous MoS2/CoxSy heterojunction in-situ grown on carbon fiber paper (CFP). Benefitting from the strong electronic interaction at the interface of crystalline MoS2 and amorphous CoxSy, the electronic structure of MoS2/CoxSy@C/CFP is optimized. Moreover, the P doping can further optimize the electronic structure and enhance water adsorption of the catalyst and lower the kinetic energy barrier of HER. The heterojunction P-MoS2/CoxSy@C/CFP can not only exhibit excellent HER activity in alkaline electrolyte but also in acidic electrolyte, with the relatively lower overpotentials of 59 mV and 135 mV at the current density of 10 mA cm−2 in 1 M KOH and 0.5 M H2SO4; 140 mV and 205 mV at the current density of 100 mA cm−2 in 1 M KOH and 0.5 M H2SO4, respectively, which the HER performance is among the best for non-precious metal-based electrocatalysts usable in both acidic and alkaline mediums. Theoretical calculations also confirm that the construction of crystalline-amorphous heterointerface between MoS2 and CoxSy and P doping can effectively accelerate the electron transport and promote the HER reaction kinetics, thus enhancing the HER performance. This construction strategy for HER electrocatalyst provides a new avenue on electrocatalytic research.

Surface engineering of Ni2P/CoP nanosheet heterojunctions by the formation of F-doped carbon layers for boosting urea-rich water electrolysis

It's highly desirable but still challenging to design bifunctional non-noble metal electrocatalysts for the hydrogen evolution reaction (HER) and urea oxidation reaction (UOR) with high activity and boosted mass transport, especially under large-current densities. Hence, a novel 3D reticular heterostructure nanosheet arrays are fabricated (Ni2P/CoP/P,F–C) through coupling the F-doped carbon to realize urea-rich water electrolysis. The interface of carbon doping F can effectively enhance the conductivity and stability of Ni2P/CoP heterojunctions along with possible changes in surface hydrophobicity to accelerate release of generated bubbles under large-current densities. Benefiting from tailored d-band center of CoP nanosheet arrays and well-designed hydrophilic-superaerophobic feature, the elaborated Ni2P/CoP/P,F–C electrode shows brilliant electrocatalytic HER (198 mV) and UOR (251 mV) performance at 100 mA cm−2 current density. Meanwhile, the assembled alkaline urea-rich water electrolyzer with Ni2P/CoP/P,F–C as both the cathode and anode present ultralow cell voltages of 1.57 V to achieve 100 mA cm−2 with long-time stability. This work will promote research interest in material design for energy conversion technologies and urea-assisted hydrogen production.

Bimetallic-MOF derived nickel-iron phosphide nanosheets on carbon cloth for efficacious oxygen evolution reaction

It is of momentously realistic significance to exploit highly efficacious and cost-effective non-noble metal electrocatalysts for oxygen evolution reaction (OER), considering its promising renewable energy application. Herein, a self-supporting electrocatalyst composed of nickel-iron phosphide nanosheets on carbon cloth (NiFeP@CC) is proposed for OER, which are derived from the phosphating treatment of two-dimensional NiFe-MOF nanosheets. The NiFeP@CC composite possesses the synergistic effect of bimetallic NiFe phosphides in promoting the OER, the fully exposed active sites of the nano-sheet structure and the fast charge/mass transfer from the hierarchical porous structure. Owing to the above structural features, the optimized NiFeP@CC presents an impressive OER performance in alkaline solution. The overpotential and Tafel slope are as low as 229 mV and 36.4 mV dec−1 under a current density of 10 mA cm−2, respectively, much superior to those for the commercial IrO2 catalyst. More excitingly, this self-supporting electrocatalyst also possesses an exceptionally high durability, showing no activity degradation for 25 h. This work offers a simple and feasible strategy for developing practically available OER catalysts with a high activity and stability.

Ni3+-enriched nickel-based electrocatalysts for superior electrocatalytic water oxidation

A good understanding of the strategy to improve the reconstruction process and catalytic mechanism of non-noble transition metal electrocatalysts in the oxygen evolution reaction (OER) is crucial to achieving high-efficiency and energy-saving hydrogen production because it is considered the rate-determining step in water splitting. In this work, Fe-doped NiO nanosheet arrays are prepared on carbon cloth (Fe/NiO/CC) by a simple solution method and subsequent sonication. The Fe dopants facilitate energy-efficient and rapid surface reconstruction, activate more Ni3+ species, and generate more oxygen vacancies to enable fast and efficient OER. As a result, an overpotential of merely 288 mV is required for a current density of 100 mA cm−2 by the Fe/NiO/CC electrocatalyst and a small Tafel slope of 72.6 mV dec−1 is observed in the alkaline electrolyte. Based on density-functional theory calculation, the difference in the bonding and charge redistribution in NiO caused by Fe dopants modulates the electronic structure and coordination unequally, consequently increasing the number of active sites and enhancing the intrinsic catalytic activity as well. The results provide a deeper understanding of how heteroatom doping modulates the intrinsic activity of active atoms in transition metal-based electrocatalysts and reveal the role in reconstruction in electrocatalytic OER.

Preparation of ultrahigh surface area carbon microspheres under solvent-free hypersaline environment for zinc-air batteries with high power density

It is of great significance to develop efficient non-noble metal electrocatalysts for oxygen reduction reaction (ORR). Herein, the starch-based carbon microspheres (CMS) electrocatalyst with ultrahigh specific surface area (SSA) of 2799 m2 g-1 is prepared by solvent-free method under hypersaline environment that composed of ZnCl2 and FeCl3·H2O. The formed carbon microspheres with hierarchical porous structure are beneficial to the adequate exposure of active sites and the free transportation of electrolyte. Importantly, the hypersaline environment favors not only the high yield of carbon material, but also the creation of abundant carbon defects with the presence of ZnFe2O4 coated on carbon microspheres, thus promoting the oxygen adsorption and desorption. The assembled zinc-air battery based on CMS2-800 exhibits prominent cycle stability, high open circuit voltage (1.43 V) and big power density (183.5 mW cm-2), superior to the battery constructed with commercialized Pt/C + RuO2. This work provides an efficient strategy to prepare electrocatalysts with starch as the starting material for high-performance zinc-air battery.