Transition Metal-based Electrocatalysts Research Articles

N-doped carbon wrapped CoFe alloy nanoparticles with MoS2 nanosheets as electrocatalyst for hydrogen and oxygen evolution reactions

Developing efficient and cost-effective transition metal-based electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is crucial to generate clean and renewable hydrogen energy. The construction of hybrid catalysts with multiple active sites is an effective approach to promote catalytic performance. Herein, a molybdenum disulfide (MoS2)-based hybrid with N-doped carbon wrapped CoFe alloy (MoS2/CoFe@NC) was synthesized through a typical hydrothermal method. The MoS2/CoFe@NC exhibits excellent electrocatalytic performance with overpotentials of 172 mV for HER and 337 mV for OER at 10 mA cm−2, and long-term stability of 24-h electrolytic reaction in 1 M KOH solution. The chemical coupling between MoS2 and CoFe@NC provides improved electronic structures and more accessible active sites. The CoFe@NC substrate accelerates the charge transfer to MoS2 through a synergistic effect. This work demonstrates that the CoFe@NC is a promising substrate for depositing MoS2 nanosheets (NSs) to achieve excellent catalytic performance for both HER and OER.

In Situ Surface Restructuring of Amorphous Ni-Doped CoMo Phosphate-Based Three-Dimensional Networked Nanosheets: Highly Efficient and Durable Electrocatalyst for Overall Alkaline Water Splitting

Developing cost-efficient bifunctional electrocatalysts with high efficiency and durability for the production of green hydrogen and oxygen is a demanding and challenging research area. Due to their high earth abundance, transition metal-based electrocatalysts are alternatives to noble metal-based water splitting electrocatalysts. Herein, binder-free three-dimensional (3D) networked nanosheets of Ni-doped CoMo ternary phosphate (Pi) were prepared using a facile electrochemical synthetic strategy on flexible carbon cloth without any high-temperature heat treatment or complicated electrode fabrication. The optimized CoMoNiPi electrocatalyst delivers admirable hydrogen (η10 = 96 mV) and oxygen (η10 = 272 mV) evolution performances in 1.0 M KOH electrolyte. For overall water splitting in a two-electrode system, the present catalyst demands only 1.59 and 1.90 V to reach current densities of 10 and 100 mA/cm2, respectively, which is lower than that of the Pt/C||RuO2 couple (1.61 V @ 10 mA/cm2, 2 V > @ 100 mA/cm2) and many other catalysts reported previously. Furthermore, the present catalyst delivers excellent long-term stability in a two-electrode system continuously over 100 h at a high current density of 100 mA/cm2, exhibiting nearly 100% faradic efficiency. The unique 3D amorphous structure with high porosity, a high active surface area, and lower charge transfer resistance provides excellent overall water splitting. Notably, the amorphous structure of the present catalyst favors the in situ surface reconstruction during electrolysis and generates very stable surface-active sites capable of long-term performance. The present work provides a route for the preparation of multimetallic-Pi nanostructures for various electrode applications that are easy to prepare and have superior activity, high stability, and low cost.

Cooperative Boron and Vanadium Doping of Nickel Phosphides for Hydrogen Evolution in Alkaline and Anion Exchange Membrane Water/Seawater Electrolyzers.

Developing low-cost and high-performance transition metal-based electrocatalysts is crucial for realizing sustainable hydrogen evolution reaction (HER) in alkaline media. Here, a cooperative boron and vanadium co-doped nickel phosphide electrode (B, V-Ni2 P) is developed to regulate the intrinsic electronic configuration of Ni2 P and promote HER processes. Experimental and theoretical results reveal that V dopants in B, V-Ni2 P greatly facilitate the dissociation of water, and the synergistic effect of B and V dopants promotes the subsequent desorption of the adsorbed hydrogen intermediates. Benefiting from the cooperativity of both dopants, the B, V-Ni2 P electrocatalyst requires a low overpotential of 148mV to attain a current density of -100mAcm-2 with excellent durability. The B, V-Ni2 P is applied as the cathode in both alkaline water electrolyzers (AWEs) and anion exchange membrane water electrolyzers (AEMWEs). Remarkably, the AEMWE delivers a stable performance to achieve 500and 1000mAcm-2 current densities at a cell voltage of 1.78and 1.92V, respectively. Furthermore, the developed AWEs and AEMWEs also demonstrate excellent performance for overall seawater electrolysis.

Lamellar-stacked cobalt-based nanopiles integrated with nitrogen/sulfur co-doped graphene as a bifunctional electrocatalyst for ultralong-term zinc-air batteries

Sluggish oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) kinetics inevitably impede the practical performance of rechargeable zinc–air batteries. Thus, combing the structural designability of transition metal-based electrocatalysts with anionic regulation is highly desired. Herein, mesoporous lamellar-stacked cobalt-based nanopiles with surface-sulfurization modification are elaborately designed and integrated with N/S co-doped graphene to build a robust OER/ORR bifunctional electrocatalyst. The lamellar-stacking mode of mesoporous nanosheets with abundant channels accelerates gas–liquid mass transfer, and partial-sulfurization of cobalt-based matrix surface efficiently improves the intrinsic OER activity. Meanwhile, N/S co-doped graphene further reinforces the ORR active sites while providing a stable conductive skeleton. As expected, this composite electrocatalyst delivers considerable bifunctional activity and stability, with an OER overpotential of 323 mV at 10 mA cm−2 and high durability. When applied in zinc–air batteries, remarkable ultralong-term stability over 4000 cycles and a maximum power density of 150.1 mW cm−2 are achieved. This work provides new insight into structure-composition synergistic design of rapid-kinetics OER/ORR bifunctional electrocatalyst for next-generation metal–air batteries.

Investigation of Charge–Discharging Behavior of Metal Oxide–Based Anode Electrocatalysts for Alkaline Water Electrolysis to Suppress Degradation due to Reverse Current

In the bipolar-type alkaline water electrolysis powered by renewable energy, electrocatalysts are degraded by repeated potential change associated with the generation of reverse current. If an electrode has large discharge capacity, the opposite electrode on the same bipolar plate is degraded by the reverse current. In this study, discharge capacity of various transition metal-based electrocatalysts was investigated to clarify the determining factors of electrocatalysts on the reverse current and durability. The discharge capacities from 1.5 to 0.5 V vs. RHE (Qdc,0.5) of electrocatalysts are proportional to the surface area in most cases. The proportionality coefficient, corresponding to the specific capacity, is 1.0 C·m–2 for Co3O4 and 2.3 C·m–2 for manganese-based electrocatalysts. The substitution of Co3+ in Co3O4 with Ni3+ increased Qdc,0.5. The upper limit of theoretical specific capacity for Co3O4 is estimated to be 1.699 C·m–2, meaning the former and latter cases correspond to 2- and 1-electron reactions, respectively, per a cation at the surface. The discharge capacities of the elctrocatalysts increased because of the dissolution and recrystallization of nickel and/or cobalt into metal hydroxides. The increase in the capacities of Co3O4 and NiCo2O4 during ten charge–discharge cycles was below 2–9% and 0.5–38%, respectively. Therefore, if a cathode electrocatalyst with relatively low redox durability is used on the one side of a bipolar plate, it is necessary to control optimum discharge capacity of the anode by changing surface area and constituent metal cations to minimize the generation of reverse current.Graphical

Thin Films Fabricated by Pulsed Laser Deposition for Electrocatalysis

Thin Films Fabricated by Pulsed Laser Deposition for Electrocatalysis

Surface reconstruction of Fe(III)/NiS nanotubes for generating high-performance oxygen-evolution catalyst

Designing high-performance and cost-effective oxygen-evolution electrocatalysts is highly required toward sustainable water electrolysis. Surface reconstruction is a promising strategy to realize the improvement of the oxygen-evolution reaction (OER) performance of transition metal-based electrocatalysts. Herein, we present a simple electrospinning-post treatment route to construct a novel Fe(III)/NiS electrocatalyst and investigate the key role of the surface reconstruction to significantly promote the OER performance. Owing to the unique tubular morphology and the formation of the highly efficient electrochemical active species of Ni(Fe)OOH during OER process, the prepared Fe(III)/NiS nanotubular catalyst exhibits a low overpotential of 264 mV at 10 mA cm−2, superior to the benchmark RuO2 and many other metal sulfide electrocatalysts. Furthermore, the catalyst also presents an excellent durability with no distinct activity reduction for over 70 h. This study offers a reliable surface reconstruction way to fabricate high-efficiency and outstanding durable OER electrocatalyst, enabling it promising prospect for water electrolysis with a reduced energy consumption.

Self-supported Ni2P/NiMoP2 bimetallic phosphide with strong electronic interaction for efficient overall water splitting

Electronic regulation via interface engineering is recognized as an attractive strategy for boosting electrocatalytic activity. In this work, a self-supported heterostructure electrocatalyst is explored by a feasible hydrothermal-pyrolysis strategy, in which Ni2P nanoparticles are anchored on NiMoP2 nanosheet arrays grown on carbon cloth (Ni2P/NiMoP2/CC). Benefitting from the nanosheet array architecture and the synergy effect between the Ni2P and NiMoP2, the as-prepared Ni2P/NiMoP2/CC manifests highly efficient activity and stability toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Density functional theory calculations further indicates that the heterointerface in Ni2P/NiMoP2/CC enable optimized interface electron structure and reduce the activation barriers for intermediates, improving the intrinsic electrocatalytic activity. Remarkably, the Ni2P/NiMoP2/CC||Ni2P/NiMoP2/CC electrolyzer affords 10 mA cm−2 at a low voltage of 1.59 V, outperforming its monometallic phosphides counterparts and most of transition metal-based bifunctional electrocatalysts. The electrolyser was powered by a solar cell to produce H2 and O2 simultaneously, indicating its potential application in solar-to-hydrogen conversion.

Amorphous Mo-doped NiS0.5 Se0.5 Nanosheets@Crystalline NiS0.5 Se0.5 Nanorods for High Current-density Electrocatalytic Water Splitting in Neutral Media.

It is vitally important to develop highly active, robust and low-cost transition metal-based electrocatalysts for overall water splitting in neutral solution especially at large current density. In this work, amorphous Mo-doped NiS0.5 Se0.5 nanosheets@crystalline NiS0.5 Se0.5 nanorods (Am-Mo-NiS0.5 Se0.5 ) was synthesized using a facil one-step strategy. In phosphate buffer saline solution, the Am-Mo-NiS0.5 Se0.5 shows tiny overpotentials of 48 and 209 mV for hydrogen evolution reaction (HER), 238 and 514 mV for oxygen evolution reaction (OER) at 10 and 1000 mA cm-2 , respectively. Moreover, Am-Mo-NiS0.5 Se0.5 delivers excellent stability for at least 300 h without obvious degradation. Theoretical calculations revealed that the Ni sites in the defect-rich amorphous structure of Am-Mo-NiS0.5 Se0.5 owns higher electron state density and strengthened the binding energy of H2 O, which will optimize H adsorption/desorption energy barriers and reduce the adsorption energy of OER determining step.

Electrolyte modification method induced atomic arrangement in FeOx/NF nanosheets for efficient overall water splitting.

To explore transition metal-based electrocatalysts with remarkable energy storage and conversion performance, the rational design and synthesis of electrodes with rich active sites and favorable electrical conductivity are crucial. Herein, using fluoroethylene carbonate (FEC) additive in electrochemical conversion reaction (electrolyte modification method) is proposed as an effective strategy to enhance the catalytic activity of FeOx/NF. The optimal sample FeOx/NF-Li-FEC1 shows optimized HER activity with remarkably low overpotential of 222 mV at a current density of 200 mA cm-2. By employing FeOx/NF-Li-FEC1 as bifunctional electrocatalysts, the overall water-splitting device reaches a current density of 10 mA cm-2 at a low cell voltage of 1.56 V. The outstanding performance is mainly attributed to the atomic arrangement to offer rich active sites as well as the evolved electronic structure and the thin SEI layer to accelerate charge transfer process. This study opens up a novel avenue to rationally design and synthesize low-cost and high-performance electrode materials for electrochemical energy conversion and storage devices.

Recent developments and prospects for engineering first-row transition metal-based catalysts for electrocatalytic NOx− reduction to ammonia

First-row transition metal-based electrocatalysts, including Cu, Fe, Co, Ni, and Ti-based electrocatalysts, for high-efficiency NOx− reduction are reviewed. These electrocatalysts should possess three advantages indicated in the figure above.

Research on engineered electrocatalysts for efficient water splitting: a comprehensive review.

Water electrolysis plays an interesting role toward hydrogen generation for overcoming global environmental crisis and solving the energy storage problem. However, there is still a deficiency of efficient electrocatalysts to overcome sluggish kinetics for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Great efforts have been employed to produce potential catalysts with low overpotential, rapid kinetics, and excellent stability for HER and OER. At present, hydrogen economy is driven by electrocatalysts with excellent characteristics; thus, systematic design strategy has become the driving force to exploit earth-abundant transition metal-based electrocatalysts toward H2 economy. In this review, the recent progress on newer materials including metals, alloys, and transition metal oxides (manganese oxides, cobalt oxides, nickel oxides, PBA-derived metal oxides, and metal complexes) as photocatalysts/electrocatalysts has been overviewed together with some methodologies for efficient water splitting. Metal-organic framework (MOF)-based electrocatalysts have been highly exploited owing to their interesting functionalities. The photovoltaic-electrocatalytic (PV-EC) process focused on harvesting high solar-to-hydrogen efficiency (STH) among various solar energy conversion as well as storage systems. Electrocatalysts/photocatalysts with high efficiency have become an urgent need for overall water splitting. Also, cutting-edge achievements in the fabrication of electrocatalysts along with theoretical consideration have been discussed.

Iron-induced lattice distortion generally boots the graphene-supported nickel phosphide nanoparticles catalysis for efficient overall water splitting

Rational design of high-efficient, low-cost and stable bifunctional electrocatalysts is necessary but challenging for water electrolysis. Transition metal phosphides (TMPs) with rich redox properties are considered to be the most promising substitutes for noble-metal materials but with aggregation and poor intrinsic electrical conductivity. Herein, we report an ultra-fast and controllable microwave strategy for synthesizing Fe-doped nickel phosphide on reduced graphene oxide (Fe-Ni12P5/rGO) as a highly active bifunctional electrocatalyst for both hydrogen and oxygen evolution reactions (HER and OER). It is noteworthy that Fe introduction can significantly cause the lattice distortion of Ni12P5 and lead to the increase of electrocatalytic active sites and modulation of the electronic structure of each catalytic center. Benefiting from the highly active Fe-Ni12P5 nanoparticles and two-dimensional graphene conductive network, the as-fabricated Fe-Ni12P5/rGO shows excellent electrocatalytic activity for HER and OER with good stability. In addition, an overall water splitting device with Fe-Ni12P5/rGO as both the cathode and anode electrocatalysts requires only an extremely low cell voltage of 1.57 V to reach 10 mA cm−2, which is attractive among the latest research. This work provides a facile and effective approach for the design of high-performance transition metal-based electrocatalysts.

Charge-Polarized Selenium Vacancy in Nickel Diselenide Enabling Efficient and Stable Electrocatalytic Conversion of Oxygen to Hydrogen Peroxide.

Vacancy engineering is deemed as one of the powerful protocols to tune the catalytic activity of electrocatalysts. Herein, Se-vacancy with charge polarization is created in the NiSe2 structure (NiSe2 -VSe ) via a sequential phase conversion strategy. By a combined analysis of the Rietveld method, transient photovoltage spectra (TPV), in situ Raman and density functional theory (DFT) calculation, it is unequivocally discovered that the presence of charge-polarized Se-vacancy is beneficial for stabilizing the structure, decreasing the electron transfer kinetics, as well as optimizing the free adsorption energy of reaction intermediate during two-electron oxygen reduction reaction (2e- ORR). Benefiting from these merits, the as-prepared NiSe2 -VSe delivered the highest selectivity of 96% toward H2 O2 in alkaline media, together with a selectivity higher than 90% over the wide potential range from 0.25 to 0.55V, ranking it in the top level among the previously reported transition metal-based electrocatalysts. Most notably, it also displayed admirable stability with only a slight selectivity decay after 5000 cycles of accelerated degradation test (ADT).

Constructing three-dimensional NiFe binary aerogel as anodic electrocatalyst for oxygen evolution reaction

Designing highly active and stable anodic electrocatalysts is of great essentiality to improve the efficiency for alkaline water electrolysis. Metal aerogels with three-dimensional structure are developing fast recently as efficient electrocatalysts but research efforts mainly focus on noble metal-based aerogels. Herein, the nonprecious NiFe aerogel is synthesized from a fast metal salt reduction-gelation method. The three-dimensional NiFe aerogel was assembled from nanosized branches, which contained NiFe alloy nanoparticles as the cores and NiFe hydroxide nanosheets as the shells. The porous NiFe aerogel can provide more surface sites and benefit the mass/charge transfer, as well as the low crystallinity in structure can provide more active sites. As the result, this NiFe aerogel demonstrated remarkable electrocatalytic activity with low overpotential of 267 mV at 50 mA cm−2 and good durability for alkaline oxygen evolution reaction, which is among the best transition metal-based OER electrocatalysts. Thus, this NiFe aerogel holds good potentials for alkaline water oxidation and brings a novel member to the family of metal aerogels.

Construction of micro-nano hierarchical wing-like iron/molybdenum oxide heterojunction with synergistic effect for accelerated overall water splitting

Designing heterojunction catalysts with high-energy interfacial effects, especially combining the geometrical advantages of hierarchical micro-nano structures with the advantages of bi- or multi-metal syergistically optimised electronic coordination environments, is crucial for achieving efficient and stable water splitting. In this study, a simple one-step hydrothermal method was used to construct a hierarchical wing-like iron/molybdenum oxide heterojunction with a porous structure on nickel foam (FMO/NF). The synergistic effect of Fe, Mo, and the heterostructures can enrich structural defects, overcome the disadvantages of the individual components, and improve material performance by optimising the structural configurations and electronic properties and exploiting the electronic interactions that occur between interfaces composed of different phases. In addition, owing to the high porosity of the hierarchical micro-nano structure and abundant active sites, the wing-like FMO/NF was utilised as an efficient bifunctional catalyst for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), presenting low overpotentials of 278.06 and 263.72 mV, respectively, at a current density of 100 mA·cm−2 in 1 mol/L KOH. Furthermore, assembling FMO/NF as both the anode and cathode (FMO/NF || FMO/NF) required a cell voltage of 1.87 V to drive 100 mA·cm−2 in 1 mol/L KOH, and it proceeded continuously for 110 h with negligible cell voltage decay. This work provides a rational synthetic route for the preparation of innovative double transition metal-based micro-nano hierarchical heterostructured electrocatalysts with a synergistic effect and further advances the development of energy-conversion technology.

Interface and cation dual-engineering promoting Ce-Co(OH)2/CoP/NF as bifunctional electrocatalyst toward overall water splitting coupling with oxidation of organic compounds

Transition metal-based electrocatalysts are the promising candidates to substitute noble metal-based catalysts for water electrolysis, owing to its abundant earth reserves and inexpensive fabrication costs. Interface engineering and cation doping engineering are verified as the effective methods to improve the sluggish electrocatalytic performance of transition metal-based electrocatalysts. Here, we synthesized a self-supported heterostructure of Ce doped Co(OH)2 nanosheets/CoP nanowires on the support of nickel foam (Ce-Co(OH)2/CoP/NF) by simple hydrothermal method, low-temperature phosphorization method. The Ce atom doping can lead to lattice distortion and abundant superficial defects on crystal surface, which will generate more active sites and faster charges transformation. The heterointerface between Ce-Co(OH)2 and CoP also can lead to electronic structure modulation at interface domain, which not can induce much fresh active sites in this area, but can optimize the active sites to the optimal state for superior catalytic activity. Benefitting from these, it only needs the overpotentials of 253 and 56 mV to realize 10 mA/cm2 for OER and HER under 1 M KOH solution, which is much enhance than single-phased samples. As the bifunctional electrocatalyst for two-electrode system, it merely requires 1.53 V to attain 10 mA/cm2 in 1 M KOH, and it also exhibits outstanding overall water splitting performance in alkaline natural electrolyte, along with excellent catalytic long-time durability. In addition, the Ce-Co(OH)2/CoP/NF-based electrolyzer also could achieve energy-saving hydrogen production, and simultaneously oxidative degradation of organic materials or biomass upgrading at anode under lower voltages. This work paves a novel idea to fabricate high-efficient bifunctional electrocatalysts for energy-saving H2 production.

Orbital Occupancy and Spin Polarization: From Mechanistic Study to Rational Design of Transition Metal-Based Electrocatalysts toward Energy Applications.

Over the past few decades, development of electrocatalysts for energy applications has extensively transitioned from trial-and-error methodologies to more rational and directed designs at the atomic levels via either nanogeometric optimization or modulating electronic properties of active sites. Regarding the modulation of electronic properties, nonprecious transition metal-based materials have been attracting large interest due to the capability of versatile tuning d-electron configurations expressed through the flexible orbital occupancy and various possible degrees of spin polarization. Herein, recent advances in tailoring electronic properties of the transition-metal atoms for intrinsically enhanced electrocatalytic performances are reviewed. We start with discussions on how orbital occupancy and spin polarization can govern the essential atomic level processes, including the transport of electron charge and spin in bulk, reactive species adsorption on the catalytic surface, and the electron transfer between catalytic centers and adsorbed species as well as reaction mechanisms. Subsequently, different techniques currently adopted in tuning electronic structures are discussed with particular emphasis on theoretical rationale and recent practical achievements. We also highlight the promises of the recently established computational design approaches in developing electrocatalysts for energy applications. Lastly, the discussion is concluded with perspectives on current challenges and future opportunities. We hope this review will present the beauty of the structure-activity relationships in catalysis sciences and contribute to advance the rational development of electrocatalysts for energy conversion applications.

Research Progress of Bifunctional Oxygen Reactive Electrocatalysts for Zinc-Air Batteries.

Zinc-air batteries (ZABs) have several advantages, including high energy density, cheap price and stable performances with good application prospects in the field of power batteries. The charging and discharging reactions for the air cathode of ZABs are the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively, which play an important role in the whole performance of ZAB. Due to the cost and limited reserves of highly active precious metal catalysts, it is crucial to design alternative efficient and stable dual-functional non-precious metal catalysts. In the present review, we present a systematic summary of the recent progress in the use of transition metal-based electrocatalysts as alternatives to precious metals for the positive poles of ZAB air. Combined with state-of-the-art in situ characterization technologies, a deep understanding of the catalytic mechanism of OER/ORR provided unique insights into the precise design of excellent synthetic non-precious metal catalysts from the perspective of atomic structure. This review further shows that the hybrid electric battery is a new strategy to improve the efficiency of the hybrid electric battery, which could be available to alleviate the problem of resource shortage. Finally, the challenges and research trends for the future development of ZABs were clearly proposed.

In Situ Growth of Self-Supporting MOFs-Derived Ni2P on Hierarchical Doped Carbon for Efficient Overall Water Splitting

The in situ growth of metal organic framework (MOF) derivatives on the surface of nickel foam is a novel type of promising self-supporting electrode catalyst. In this paper, this work reports for the first time the strategy of in situ growth of Ni-MOF, where the metal source is purely provided by a nickel foam (NF) substrate without any external metal ions. MOF-derived Ni2P/NPC structure is achieved by the subsequent phosphidation to yield Ni2P on porous N, P-doped carbon (NPC) backbone. Such strategy provides the as-synthesized Ni2P/NPC/NF electrocatalyst an extremely low interfacial steric resistance. Moreover, a unique three-dimensional hierarchical structure is achieved in Ni2P/NPC/NF, providing massive active sites, short ion diffusion path, and high electrical conductivity. Directly applied as the electrode, Ni2P/NPC/NF demonstrates excellent electrocatalytic performance towards both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), with low overpotentials of only 58 mV and 208 mV to drive 10 mA cm−2, respectively, in 1 M KOH. Furthermore, Ni2P/NPC/NF acting as the overall water splitting electrodes can generate a current density of 10 mA cm−2 at an ultralow cell voltage of 1.53 V. This simple strategy paves the way for the construction of self-supporting transition metal-based electrocatalysts.