Oxygen Evolution Reaction In Alkaline Electrolyte Research Articles

Ultrafast synthesis of biphase Ni-doped FeOOH for efficient and stable oxygen evolution at high current density

NiFe oxyhydroxides, generally reconstructed on surface during oxygen evolution reaction (OER), are real active species for water oxidation; however, their direct and convenient preparation remains challenging. Here, we develop a one-step approach to prepare biphase (α/δ) Ni-doped FeOOH catalyst in 3 min under room temperature. The core of this ultrafast method is that Fe2+ derived from the redox reaction of Fe3+ and Ni2+ accelerate Fenton-like reaction, while simultaneously producing mixed-valence Ni ions(Ni2+, Ni3+) results in not only homovalent and heterovalent doping, but also biphase Ni-doped FeOOH heterojunction with high and low crystallinity. Specifically, Ni2+ doping leads to a preferred formation of low-crystalline δ-oriented Ni-doped FeOOH with abundant oxygen vacancies, which is in favor of triggering the lattice oxygen mechanism (LOM) during OER. Benefitting from high/low crystalline biphase heterojunction and LOM, the optimized Ni-FeOOH merely needs low overpotential of 300 mV to reach 1000 mA cm−2 for OER in alkaline electrolyte and also shows excellent durability even at a high current density of 500 mA cm−2. This work provides a cost-effective strategy to fabricate highly active and robust non-noble electrocatalysts that can potentially be applied for industrial-scale OER electrolysis.

Bifunctional Noble-Metal Free Ternary Chalcogenide Electrocatalysts for Water Splitting

With the ever-increasing global energy demand, the development of renewable energy technologies is crucial to fulfilling the energy requirements in a sustainable manner. Hydrogen has emerged as a promising energy carrier that can provide emission-free energy for end-use applications. Among the several pathways of hydrogen production, green hydrogen production by electrochemical water splitting using renewable energy is an emission-free, efficient energy conversion technology. Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) occur at the cathode and anode, respectively. Water splits into hydrogen and oxygen at the thermodynamic potential of 1.23 V; however, overpotentials are observed experimentally due to the kinetic barriers, which increases the required potential for water splitting. Catalysts lower the required overpotentials, making the process more energy efficient. A significant issue with large-scale hydrogen production by water electrolysis is that the state-of-the-art catalysts for HER and OER are based on precious metals and thus are limited by their high cost and net production capacity. Thus, there is a lot of interest in developing noble-metal-free electrocatalysts based on earth-abundant materials that can efficiently lower the associated overpotentials for the two halves of the water-splitting reaction.A large number of late transition metal-based ternary complex oxides have been investigated for their catalytic performance towards water splitting, where fine-tuning of the properties using compositional engineering has been demonstrated. Binary sulfides, selenides, and phosphides have also been explored as candidates for water splitting. Recently, early transition metal-based ternary complex materials have emerged as a novel class of electronic materials with applications in infrared optics and photovoltaics. However, similar chalcogenide compositions based on late-transition metals remain underexplored.We have synthesized a series of LaMS3 (M = Mn, Fe, Co, Ni) materials by high-temperature sulfurization of corresponding ternary oxides, using carbon disulfide (CS2) as the sulfurizing agent. The LaMS3 compounds are isostructural and crystallize in the hexagonal P 63 space group. When tested for catalytic performance towards water splitting, they demonstrate good activity towards both HER and OER, with LaNiS3 (LNS) being the most active material, and a periodic activity trend is observed, where LNS > LCS >> LFS > LMS. For OER in alkaline electrolyte, LNS demonstrates an overpotential of 373 mV at 10mA/cm2 in 1.0 M KOH, and a low Tafel slope value of 48 mV/dec. The long-term stability was tested using chronopotentiometry measurements, and LNS shows excellent stability, with negligible change in overpotential over several hours. For HER testing in both acidic and alkaline electrolyte, LNS again seems to be the most active material, and a periodic activity trend in the HER activity of LaMS3 materials, similar to the OER activity trend, is observed. LNS has an overpotential of 340 mV in 0.5 M H2SO4 and 362 mV in 1.0 M KOH, indicating that LNS is catalytically active over a wide range of pH levels. LNS also shows excellent long-term stability towards HER in both acidic and alkaline electrolyte. We also compared the activity of LaMS3 materials with their ternary oxide counterparts from which they were synthesized, and the LaMS3 compounds outperform the LaMO3 compounds, demonstrating lower overpotentials and Tafel slope values for both HER and OER, with the HER overpotentials for LaMO3 materials being > 250 mV higher compared to LaMS3, for both acidic and alkaline electrolytes. The catalytic activity of the LaMS3 series towards both HER and OER, along with their excellent long-term stability, makes these materials promising candidates for bifunctional electrocatalysts for water splitting while offering a wide compositional range that allows for further optimization of their performance.

Structural Reconstruction of a Cobalt- and Ferrocene-Based Metal-Organic Framework during the Electrochemical Oxygen Evolution Reaction.

Metal-organic frameworks (MOFs) are increasingly being investigated as electrocatalysts for the oxygen evolution reaction (OER) due to their unique modular structures that present a hybrid between molecular and heterogeneous catalysts, featuring well-defined active sites. However, many fundamental questions remain open regarding the electrochemical stability of MOFs, structural reconstruction of coordination sites, and the role of in situ-formed species. Here, we report the structural transformation of a surface-grown MOF containing cobalt nodes and 1,1'-ferrocenedicarboxylic acid linkers (denoted as CoFc-MOF) during the OER in alkaline electrolyte. Ex situ and in situ investigations of CoFc-MOF film suggest that the MOF acts as a precatalyst and undergoes a two-step restructuring process under operating conditions to generate a metal oxyhydroxide phase. The MOF-derived metal oxyhydroxide catalyst, supported on nickel foam electrodes, displays high activity toward the OER with an overpotential of 190 mV at a current density of 10 mA cm-2. While this study demonstrates the necessity of investigating structural evolution of MOFs during electrocatalysis, it also shows the potential of using MOFs as precursors in catalyst design.

Oxygen-bridging Fe, Co dual-metal dimers boost reversible oxygen electrocatalysis for rechargeable Zn–air batteries

Rechargeable zinc-air batteries (ZABs) are regarded as a remarkably promising alternative to current lithium-ion batteries, addressing the requirements for large-scale high-energy storage. Nevertheless, the sluggish kinetics involving oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) hamper the widespread application of ZABs, necessitating the development of high-efficiency and durable bifunctional electrocatalysts. Here, we report oxygen atom-bridged Fe, Co dual-metal dimers (FeOCo-SAD), in which the active site Fe-O-Co-N6 moiety boosts exceptional reversible activity toward ORR and OER in alkaline electrolytes. Specifically, FeOCo-SAD achieves a half-wave potential (E1/2) of 0.87 V for ORR and an overpotential of 310 mV at a current density of 10 mA cm-2 for OER, with a potential gap (ΔE) of only 0.67 V. Meanwhile, FeOCo-SAD manifests high performance with a peak power density of 241.24 mW cm-2 in realistic rechargeable ZABs. Theoretical calculations demonstrate that the introduction of an oxygen bridge in the Fe, Co dimer induced charge spatial redistribution around Fe and Co atoms. This enhances the activation of oxygen and optimizes the adsorption/desorption dynamics of reaction intermediates. Consequently, energy barriers are effectively reduced, leading to a strong promotion of intrinsic activity toward ORR and OER. This work suggests that oxygen-bridging dual-metal dimers offer promising prospects for significantly enhancing the performance of reversible oxygen electrocatalysis and for creating innovative catalysts that exhibit synergistic effects and electronic states.

Nanoflowers of Ternary Cobalt–Copper–Manganese Oxide as an Efficient Electrocatalyst for Oxygen Evolution Reaction

Oxygen evolution reaction (OER) is an integral step in the water‐splitting process. Hence, to promote OER, efficient catalysts are required to lower the energy barriers at the electrode/electrolyte interface. Low‐cost and highly active catalysts are in great demand. Herein, a ternary metal oxide, CoCuMnOx, synthesized by a facile hydrothermal method is reported, which possesses excellent catalytic ability for OER in alkaline electrolytes. The nanoscale morphology of the catalyst with flower‐like nanostructures is instrumental in increasing the electrochemical surface area of the electrode. The presence of multivalent ions and the incorporation of copper greatly enhance the electrochemical properties of the catalysts. The catalysts typically demonstrate an overpotential value of 220 mV for achieving 10 mA cm−2 current density and a Tafel slope of 73 mV dec−1. The catalysts demonstrate good stability with minimal degradation in OER activity even after 20 h of chronopotentiometry test. For practical applications, this low‐cost material holds great potential.

Zirconium (Oxy)Nitrides for (Photo)Electrochemical Applications

Transition metal (TM) nitrides are an emerging class of (photo)electrocatalytic materials that have recently received growing research interest.1,2 In general, nitrogen-poor TM nitrides are usually refractory materials with metallic character while nitrogen-rich nitrides often possess semiconducting character.3 Hence, while the former are potential electrocatalyst candidates, the latter may qualify as photoelectrode absorber materials. For example, ZrN has recently been proposed as an electrocatalyst for both the electrochemical nitrogen4 and oxygen5 reduction reactions (ORR and NRR), while Zr3N4 and also Zr2N2O have been suggested as potential photoanode materials in photoelectrochemical water oxidation.2 In this contribution, we test these hypotheses regarding the (photo)electrochemical characteristics of Zr-based (oxy)nitrides by experiment. To this end, we investigate reactively sputtered thin films for the electrochemical NRR/ORR and the photoelectrochemical oxygen evolution reaction (OER). Previous experiments on Ta-based nitrides have shown that addition of oxygen during the reactive sputter process is necessary to access higher metal oxidation states.6 As we introduce controlled amounts of oxygen at otherwise fixed deposition conditions, we observe a transition from metallic ZrN to a disordered nitrogen-rich ZrxNy to a crystalline bixbyite-type Zr2N2O to nitrogen-doped cubic ZrO2. Crystalline Zr3N4 was not accessible under the used experimental conditions. In our experiments, we observe a lack of electrocatalytic activity for ZrN in NRR and ORR and instabilities of the disordered nitrogen-rich ZrxNy in the photoelectrochemical OER. Introducing more oxygen into the structure, however, leads to a more stable crystalline structure (Zr2N2O), the opening of a band gap in the visible range, and the emergence of photoelectrochemical activity for oxidation reactions. Based on chopped linear sweep voltammetry measurements, we show that Zr2N2O films are photoactive for the OER in alkaline electrolyte with low onset potentials, indicating an overall favorable band alignment of the material with respect to the water oxidation and reduction potentials. While the observed photocurrents are still about one order of magnitude lower than for the benchmark oxynitride photoanode TaON, further material optimization could potentially close this gap and provide a materials system functioning as sustainable photoanode.References 1 W. Sun, C.J. Bartel, E. Arca, S.R. Bauers, B. Matthews, B. Orvañanos, B.R. Chen, M.F. Toney, L.T. Schelhas, W. Tumas, J. Tate, A. Zakutayev, S. Lany, A.M. Holder, and G. Ceder, Nat. Mater. 18, 732 (2019). 2 Y. Wu, P. Lazic, G. Hautier, K. Persson, and G. Ceder, Energy Environ. Sci. 6, 157 (2013). 3 A. Salamat, A.L. Hector, P. Kroll, and P.F. McMillan, Coord. Chem. Rev. 257, 2063 (2013). 4 Y. Abghoui, A.L. Garden, J.G. Howalt, T. Vegge, and E. Skúlason, ACS Catal. 6, 635 (2016). 5 Y. Yuan, J. Wang, S. Adimi, H. Shen, T. Thomas, R. Ma, J.P. Attfield, and M. Yang, Nat. Mater. 19, (2019). 6 C.M. Jiang, L.I. Wagner, M.K. Horton, J. Eichhorn, T. Rieth, V.F. Kunzelmann, M. Kraut, Y. Li, K.A. Persson, and I.D. Sharp, Mater. Horizons 8, 1744 (2021).

Fe7C3 nanoparticles anchored on N-doped biochar as electrocatalyst for highly efficient oxygen evolution reaction

As the crucial step of electrolytic water, oxygen evolution reaction (OER) is urgent to be enhanced by developing the most efficient electrocatalysts to accelerate the sluggish OER kinetics. Herein, nitrogen-doped carbon-based Fe7C3 clusters with hierarchical pore structure (NHAC@Fe7C3) were synthesized via a two-step method of FeCl3 and seaweed liquid-phase impregnation combined with physical activation. The optimum NHAC@Fe7C3 = 3:1 catalyst (with a mass ratio of Sargassum Horneri to FeCl3 of 3:1) demonstrated much better catalytic activity and durability towards OER in alkaline electrolyte than the most noble-metal-free catalysts, of which the overpotential reached 181 mV at 10 mA cm−2. Long-term discharging stability of over 33 h at 10 mA cm−2 current density. The excellent performance is attributed to the synergistic effect of graphitic carbon and Fe7C3 clusters, hierarchical pore structure and good electrical conductivity. Density functional theory calculations confirm that the free energy for the potential-limiting step is reduced by the synergistic effect of N-doped carbon and Fe7C3 substrance. This study employs a simple and effective method to synthesize iron carbide embedded in algae-derived biochar, providing an opportunity for the rational design of robust performance electrocatalysts for oxygen evolution reaction.

Exciting lattice oxygen of nickel–iron bi-metal alkoxide for efficient electrochemical oxygen evolution reaction

High efficiency, cost-effective and durable electrocatalysts are of pivotal importance in energy conversion and storage systems. The electro-oxidation of water to oxygen plays a crucial role in such energy conversion technologies. Herein, we report a robust method for the synthesis of a bimetallic alkoxide for efficient oxygen evolution reaction (OER) for alkaline electrolysis, which yields current density of 10 mA cm−2 at an overpotential of 215 mV in 0.1 M KOH electrolyte. The catalyst demonstrates an excellent durability for more than 540 h operation with negligible degradation in activity. Raman spectra revealed that the catalyst underwent structure reconstruction during OER, evolving into oxyhydroxide, which was the active site proceeding OER in alkaline electrolyte. In-situ synchrotron X-ray absorption experiment combined with density functional theory calculation suggests a lattice oxygen involved electrocatalytic reaction mechanism for the in-situ generated nickel–iron bimetal-oxyhydroxide catalyst. This mechanism together with the synergy between nickel and iron are responsible for the enhanced catalytic activity and durability. These findings provide promising strategies for the rational design of non-noble metal OER catalysts.

Cyanogel-Based Preparation of Amorphous NiFe Nanoaggregates with Enhanced Activity and Stability for OER

The development of cost-efficient electrocatalysts for oxygen evolution reaction (OER) with high efficiency is crucial to widespread applications of water splitting for hydrogen production. In this work, porous three-dimensional (3D) amorphous NiFe nanoaggregates composed of interconnected nanograins were synthesized by a cyanogel-based wet chemical reduction method using the NiCl2/Na4Fe(CN)6 cyanogel as the precursor and NaBH4 as the reducing agent. The influence of the incorporated Fe amount was carefully studied by slightly changing the feeding molar ratios of the Ni/Fe atoms in the precursors. The intrinsic 3D backbone structure of the cyanogel resulted in crystal nuclei tending to generate along with the backbones, which is key to the formation of NiFe nanoaggregates with a porous 3D interconnected structure. The synthesized NiFe nanoaggregates with a 3D interconnected structure and high porosity, as well as the incorporation of Fe, are in favor of high surface area, more active sites, and abundant oxygen vacancies, leading to superior activity and stability of OER in alkaline electrolytes with a low overpotential of 0.35 V at 10 mA cm−2, a high current density of 24.8 mA cm−2 at 1.65 V, a small Tafel slope of 76.9 mV dec−1, and attractive durability in 1 M KOH solution.

Simply embedding α-Fe2O3/Fe3O4 nanoparticles in N-doped graphitic carbon polyhedron layered arrays as excellent electrocatalyst for rechargeable Zn-air battery

Hybrids of α-Fe2O3/Fe3O4 nanoparticles embedded in N doped graphitic carbon polyhedron layered arrays (FeOx/NCLA) were simply constructed by pyrolyzing the composite precursor of NH2-MIL-101(Fe) (a metal organic framework, MOF) and glycylglycine. The experimental and calculated results reveal that the obtained catalysts exhibited multiple active components, synergistic heterojunction effect, high BET surface areas and conductivity, and consequently greatly improved intrinsic electrocatalytic activities and kinetics for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). As the results, the optimized catalyst FeOx/NCLA-1.2 exhibited positive half-wave potential of 0.846 V for ORR and only 218 mV of overpotential (at 10 mA/cm2) for OER in alkaline electrolyte, which is superior than Pt/C (20 %) and RuO2, respectively. The Zn-air battery (ZAB) employing the FeOx/NCLA-1.2 as electrocatalyst obtained a peak power density of 104.3 mW·cm−2, a specific capacity of 840 mAh·gZn-1 and an energy density of 890 Wh·kgZn-1, which is also much higher than that for the noble metal based one. The catalyst is promised to be applied in water electrolysis, fuel cells and metal-air batteries.

MOF-derived ultrasmall Ru@RuO2 heterostructures as bifunctional and pH-universal electrocatalysts for 0.79 V asymmetric amphoteric overall water splitting

Developing heterostructures in nano-electrocatalyst has been demonstrated as a feasible method to enhance electrocatalytic activities for water splitting, since it still remains a grand challenge to develop highly efficient and stable electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) within a wide pH range. Herein, we report a facile pyrolysis strategy of Ru-MOF for rationally constructing ultrasmall Ru@RuO2 heterostructures, which exhibit extremely remarkable electrocatalytic performance toward both HER and OER in pH-universal electrolytes. Impressively, optimal Ru@RuO2-250 achieves ultralow overpotentials for both OER (198 mV, 263 mV and 182 mV @ 10 mA cm−2 in acidic, neutral and alkaline media) and HER (31 mV, 43 mV and 32 mV @ 10 mA cm−2 in acidic, neutral and alkaline media) due to the full exposure of highly active sites, which are derived from the synergism of abundant heterointerfaces, ultrafine heterostructure size and hierarchical porous structure with high surface area. Theoretical calculations reveal the charge rearrangement and electron conduction intensification near Ru-RuO2 heterointerfaces, the electronic structure changes of the active sites optimize the adsorption behavior toward various reaction intermediates, reducing the activation barriers and speeding up the reaction kinetics. Deservedly, an asymmetric-electrolyte electrolyzer employed with Ru@RuO2-250 is assembled to acquire an ultralow applied voltage of 0.79 V at 10 mA cm−2 based on amphoteric water electrolysis (HER in acidic electrolyte while OER in alkaline electrolyte).

Novel transition-metal phosphides@N, P-codoped carbon electrocatalysts synthesized via a universal strategy for overall water splitting

Developing highly efficient and stable bifunctional electrocatalysts plays a crucial role in water splitting reaction. Benefiting from their abundant reserves, superior conductivity and excellent intrinsic catalytic properties, transition metal phosphides (TMPs) draw wide attentions in recent years. However, most of TMPs synthesis processes are still acomplicated and dangerous as the common use of toxic and flammable phosphorus sources. Herein, we propose a universal and scalable synthetic strategy to prepare a series of nanosized transition metal phosphide encapsulated in nitrogen-phosphorus co-doped carbon (TMP@NPC) catalysts by using green and inexpensive adenosine triphosphate (ATP) as a new phosphorus source. Profiting from the in situ and confined synthetic strategy, as-prepared TMP@NPC catalysts not only show nanosized dimension, but also endow extremely intimate interaction with N, P component derived from ATP. All as-prepared TMP@NPC catalysts exhibit excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities with small overpotentials and robust capabilities. Especially, the CoP@NPC displays the lowest overpotentials of 184.35 mV and 303 mV at 10 mA cm−2 toward HER and OER in alkaline electrolyte, respectively, which also exhibits outstanding stability (over 50 h at 10 mA cm−2) in both reactions. As a proof of further application, as-prepared CoP@NPC acting as both cathode and anode shows excellent performance in overall water splitting. This work not only highlights the green and general synthesis strategy importance in designing and constructing TMPs, but also reinforces the understanding of intimate interaction in coupled hybrid electrocatalysts.

Fe doped NiSe2 nanoarrays to boost electrocatalytic oxygen evolution reaction

• Fe doped NiSe 2 on carbon cloth (CC) catalysts were synthesized by a two-step hydrothermal method. • Ni 0.8 Fe 0.2 Se 2 /CC is evidenced by the overpotential of 257 mV at the current density of 10 mA cm −2 , and Tafel slope of 43 mV dec −1 . • Doping engineering strategy makes Ni 0.8 Fe 0.2 Se 2 /CC manifest a superb performance for OER. • Ni 0.8 Fe 0.2 Se 2 transforms into NiFe-based (oxy)hydroxides, which serves as “real” active phase. Transition metal selenides (TMSes) have attracted increasing attention for electrocatalysts due to fascinating properties, such as low cost, intrinsic metallic properties, and high catalytic activities. In addition, bimetallic selenides exhibit more excellent performance in the oxygen evolution reaction (OER) process than monometallic selenides via synergistic effect. Herein, we synthesized Fe doped NiSe 2 on carbon cloth (CC) employed as electrodes for boosting OER by a facile two-step hydrothermal method. These electrodes display excellent electrocatalytic activity for OER in alkaline electrolytes, in which Ni 0.8 Fe 0.2 Se 2 /CC is evidenced by the overpotential of 257 mV at the current density of 10 mA cm −2 , and Tafel slope of 43 mV dec −1 . The synthesized three-dimensional structure with the aid of carbon cloth helps for the mass and charge transfer. Furthermore, Fe doping not only induces stronger electron interaction but tunes electronic structure, thus improving the OER performance. After a long-term OER process, Ni 0.8 Fe 0.2 Se 2 transforms into NiFe-based (oxy)hydroxides, which may serve as “real” active phase. Doping engineering strategy makes TMSes manifest a superb performance for OER and expands ways for designing effective OER electrodes. Herein, we synthesized Fe doped NiSe 2 on carbon cloth (CC) employed as electrodes for boosting OER by a facile two-step hydrothermal method. These electrodes display excellent electrocatalytic activity for OER in alkaline electrolytes, in which Ni 0.8 Fe 0.2 Se 2 /CC is evidenced by the overpotential of 257 mV at the current density of 10 mA cm −2 , and Tafel slope of 43 mV dec −1 . Fe doping not only induces stronger electron interaction but enlarges Ni 3+ /Ni 2+ ratio, thus improving the OER performance. Ni 0.8 Fe 0.2 Se 2 transforms into NiFe-based (oxy)hydroxides, which serve as “real” active phase in OER process.

Computational atomic‐scale design and experimental verification for layered double hydroxide as an efficient alkaline oxygen evolution reaction catalyst

Electrochemical water splitting is one of the most efficient techniques to produce hydrogen in an environmentally friendly way. However, a sluggish anodic reaction, namely oxygen evolution reaction (OER), requires the use of an efficient electrocatalyst for achieving economic hydrogen production. Transition-metal-based layered double hydroxides (LDHs) are promising electrocatalysts for reducing the overpotential of OER in alkaline electrolyte, which is essential for efficient water electrolysis. Nickel-iron-based LDHs (Ni-Fe LDH) have been regarded as the best OER electrocatalysts under alkaline conditions. Hence, a number of research studies have been conducted on further improving the electrocatalytic performance of Ni-Fe LDH. Although the chemical blending of other transition metals with Ni-Fe-LDH is a simple and reliable strategy to enhance the OER activity of Ni-Fe-LDH, a systematic investigation on designing Ni-Fe-LDH with different additional elements is still lacking. In addition, the design of multi-metallic LDH compound via only experimental method is very costly and time-consuming process. In this study, atomic-scale computational and experimental studies are performed to design OER electrocatalysts including unary, binary, and ternary LDH compounds consisting of Ni, Fe, Al, and Co. Density functional theory calculations predict that Ni-Fe-Co ternary LDH can lead to the lowest overpotential for alkaline OER among various computationally modeled LDH systems. Further, experimental verifications successfully demonstrate the computational prediction wherein Ni-Fe-Co-LDH exhibits superior catalytic performance compared with Ni-Fe-LDH and benchmark IrO2 catalysts.

Encapsulation of Fe-CoP with P, N-co-doped porous carbon matrix as a multifunctional catalyst for wide electrochemical applications

Hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) serve as the most promising electrochemical processes for renewable energy. Developing multifunctional electrocatalysts with high performance for HER, OER and ORR still remains a challenge. Herein, we report a facile method to prepare P, N-co-doped porous carbon encapsulated Fe-CoP (A-Fe-CoP/CPN) electrocatalyst through freeze drying, carbonization, and KOH activation. The acquired A-Fe-CoP/CPN possesses abundant pores with large surface area, which provides sufficient defect-rich sites for HER, OER, and ORR, in alkaline or acidic electrolytes. The A-Fe-CoP/CPN shows low overpotential and good stability for HER and OER in alkaline electrolyte. Density functional theory (DFT) computations reveal that the addition of Fe greatly facilitates the rate-determining step and overall catalytic pathway for both HER and OER. A-Fe-CoP/CPN also exhibits low half-wave potential (E1/2) for ORR, which indicates an enhanced performance than that of the noble Pt/C catalyst. Zn-air battery equipped with the A-Fe-CoP/CPN catalyst exhibits a high energy density (849 mAh g−1) and a long-time stability at 5 mA cm−2. This finding not only offers a facile strategy to prepare porous carbon materials with defect-rich sites, but also provides guidance for developing multifunctional electrocatalysts for wide electrochemical reactions.

Interface engineering induced electrocatalytic behavior in core-shelled CNTs@NiP2/NbP heterostructure for highly efficient overall water splitting

Earth-abundant and efficient bifunctional electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) are crucial for electrochemical water splitting to produce green hydrogen fuel. In this work, core–shell heterostructure catalyst by NiP2/NiP nanosheets shelled carbon nanotubes supported on three-dimensional framework were prepared by new effective approach. Benefiting from the unique morphological feature of carbon nanotubes architecture, the synergy of inner carbon nanotubes and outer NiP2/NiP nanosheets, and the good couple interactions at interface between NiP2 and NbP phases, this electrocatalyst showed low overpotential of 137.0 and 248.2 mV for HER and OER at a current density of 20 mA cm−2, respectively. These overpotentials were one of the smallest values of noble-metal-free electrocatalyst for HER and OER in alkaline electrolyte. Moreover, when the advanced catalyst was assembled in two-electrode configuration for full water electrolysis, a very low cell voltage of 1.51 V was required to achieve 10 mA cm−2 current density and a higher current density of 100 mA cm−2 was reached at a cell voltage of only 2.32 V.

An integrated optimization of composition and pore structure boosting electrocatalytic oxygen evolution of Prussian blue analogue derivatives

Exploring efficient and low-cost electrocatalysts for oxygen evolution reaction (OER) is of great importance for renewable energy-related systems. Prussian blue analogues (PBAs) are considered as promising precursors to derive advanced heteroatom-doped carbonaceous materials. However, the pyrolysis treatment usually results in an inevitable aggregation of active sites as well as the reduction of specific surface area, apart from the uncontrollable composition and morphology. Herein, we develop a straightforward synthetic protocol for fabricating highly-active OER electrocatalysts of Co7Fe3, Co, N-codoped carbon (Co7Fe3/Co@NC) by annealing trimetallic CoZnFe-PBA precursors. The surface modification of cobalt species over ZnFe-PBA effectively tailors the active composition for as-derived products, whereas Zn volatilization at a high temperature not only promotes the dispersion of active sites but also fabricates the formation of an intriguing hierarchical structure with multimodal porosity and high specific surface area. The integrated advantages of multinary composition and fabulous pore structure endow the elegantly-designed Co7Fe3/Co@NC with a remarkable catalytic performance towards OER in alkaline electrolyte, as evidenced by an overpotential of 290 mV without iR-correction at a current density of 10 mA cm−2 and impressive long-term durability. The present synthetic strategy offers valuable insights for developing highly-efficient PBAs-derived electrocatalysts with compositional multiplicity and interesting pore texture.

Electrospinning construction of heterostructural Co3W3C/CoP nanoparticles embedded in N, P-doped hierarchically porous carbon fibers as excellent multifunctional electrocatalyst for Zn-air batteries and water splitting

A series of heterostructural Co 3 W 3 C/CoP nanoparticles embedded in N, P-doped hierarchically porous carbon fibers were fabricated facilely as excellent multifunctional electrocatalysts. The optimal sample CoWCP-NPC-2:1 exhibited highly efficient catalytic activities for HER, OER, ORR, overall water splitting and Zn-air batteries. • The preparing procedure is simple. • The interfacial engineering is employed. • Synergistic effect beween the muti-composition has been shown. • The catalysts show excellent multifunctional performances on ORR, OER and HER. • Broad application prospects in Zn–air batteries and water electrolysis are expected. In this work, facile electrospinning method has been adopted to construct the interfacial engineering heterostructures of Co 3 W 3 C/CoP nanoparticles embedded in N, P-doped hierarchically porous carbon fibers, in which abundant interfaces and multiple active sites were formed. The fabricated catalysts Co 3 W 3 C/CoP/NPC have shown prominent trifunctional electrocatalytic activities for hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), evidenced by a positive half-wave potential of 0.803 V for ORR and a much low overpotential (at 10 mA/cm 2 ) of 139/200 mV for HER and OER in alkaline electrolyte, respectively. Furthermore, the rechargeable zinc-air battery based on the optimum CoWCP-NPC-2:1 catalyst has shown a prominent high power density of 205.5 mW/cm 2 and a specific capacity of 800.5 mAh·g −1 after 83.5 h/501 cycles at 10 mA/cm 2 . When the catalyst CoWCP-NPC-2:1 was employed as anode and cathode electrocatalysts for overall water splitting, only 1.49 V of cell voltage was needed to reach 10 mA/cm 2 . This work will provide inspiration for the design of advanced, multifunctional, and performance-oriented heterogeneous catalysts in sustainable energy conversion technology.

Ultrafast Room-Temperature Synthesis of Self-Supported NiFe-Layered Double Hydroxide as Large-Current-Density Oxygen Evolution Electrocatalyst.

Water splitting is a promising sustainable technology to produce high purity hydrogen, but its commercial application remains a giant challenge due to the kinetically sluggish oxygen evolution reaction (OER). In this work, a time- and energy-saving approach to directly grow NiFe-layered double hydroxide (NiFe-LDH) nanosheets on nickel foam under ambient temperature and pressure is reported. These NiFe-LDH nanosheets are vertically rooted in nickel foam and interdigitated together to form a highly porous array, leading to numerous exposed active sites, reduced resistance of charge/mass transportation and enhanced mechanical stability. As self-supported electrocatalyst, the representative sample (NF@NiFe-LDH-1.5-4) shows an excellent large-current-density catalytic activity for OER in alkaline electrolyte, requiring low overpotentials of 190 and 220 mV to reach the current densities of 100 and 657 mA cm-2 with a Tafel slope of 38.1 mV dec-1 . In addition, NF@NiFe-LDH-1.5-4 as an overall water splitting electrocatalyst can stably achieve a large current density of 200 mA cm-2 over 300 h at a low cell voltage of 1.83 V, meeting the requirement of industrial hydrogen production. This exceedingly simple and ultrafast synthesis of low-cost and highly active large-current-density OER electrocatalysts can propel the commercialization of hydrogen producing technology via water splitting.

Benchmarking superfast electrodeposited bimetallic (Ni, Fe, Co, and Cu) hydroxides for oxygen evolution reaction

High-performing electrocatalysts of oxygen evolution reaction (OER) are essential for various clean energy devices. Due to their excellent OER performance, transition metal layered doubled hydroxides (LDHs) attract increasing interest. Herein, a systematic study of superfast single-step synthesis for a series of carbon-free, binder-free self-supported bimetallic hydroxides on Ni foam (NF) and their associated performance towards OER in alkaline electrolytes is presented. Transition metal hydroxides are directly deposited on NF by a superfast electrodeposition technique. The resultant bimetallic hydroxides are uniformly distributed over NF in short-range order crystalline or amorphous structures. All six electrodes demonstrate significantly greater OER activities than ruthenium oxide (RuO2). The interaction between transition metal LDHs and NF determines OER performance. Applying optimum conditions, the highest activities are accomplished. Overall, results show excellent OER performance. The fast electrodeposition technique provides a systematic and cost-effective way to achieve durable self-supported transition metal LDH structures showing excellent OER performance.