Electrocatalysts For OER Research Articles

Self-supported N-doped hierarchical Co3O4 electrocatalyst with abundant oxygen vacancies for acidic water oxidation

The development of low-cost, efficient and robust non-precious metal electrocatalysts for acidic oxygen evolution (OER) is a major challenge. A novel self-supported N-doped hierarchical Co3O4 (3D Co3O4/NC-250) electrocatalyst with abundant oxygen vacancies was prepared by a facile carbonization-oxidation process. XAFS and EPR results clarified that N doping regulated electronic state of central Co atom to generate abundant oxygen vacancies, which activated lattice oxygen in the water oxidation process. The key intermediate O*O was observed via in-situ ATR-FTIR, providing direct evidence for LOM mechanism on active oxygen vacancy sites. DFT calculations showed that LOM mechanism on oxygen vacancy sites was conducive to reduce adsorption free energy of oxygen-containing intermediates in limiting steps of acidic OER process. The as-prepared 3D Co3O4/NC-250 electrocatalyst exhibited ultra-high OER performance with a low overpotential of 225 mV at 10 mA cm−2 in acidic media. This study provided a new insight to rational design of efficient transition metal-based electrocatalysts for acidic OER.

Iron Oxyhydroxide: Structure and Applications in Electrocatalytic Oxygen Evolution Reaction

AbstractOxygen evolution reaction (OER) is the anodic half‐reaction for crucial energy devices, such as water electrolysis, metal–air battery, and electrochemical CO2 reduction. Fe‐based materials are recognized as one of the most promising electrocatalysts for OER because of its extremely low price and high activity. In particular, iron oxyhydroxide (FeOOH) is not only highly active toward OER, but also widely accepted as the true active species of Fe‐based OER electrocatalysts for plenty of Fe‐based materials are converted into FeOOH during OER test. Herein, the recent advances of FeOOH‐based nano‐structure and its application in OER are reviewed. The relationship between FeOOH structure and its catalytic performance, followed by the introduction of current strategies for enhancing the OER activity (i.e., crystalline phase engineering, element doping, and construction of hybrid materials) is mainly focused. Finally, a summary and perspective about the remaining challenges and future opportunities in this area and further the design of Fe‐based OER electrocatalysts are provided.

Hierarchically Structured CoNiP/CoNi Nanoparticle/Graphene/Carbon Foams as Effective Bifunctional Electrocatalysts for HER and OER

The rational assembly of multiple active components has been regarded as a feasible approach to constructing effective electrocatalysts for overall water splitting. In this work, we have first developed effective bifunctional electrocatalysts, namely, hierarchically structured CoNiP/CoNi nanoparticle/graphene/carbon foams. Reduced graphene oxide nanosheets like papers encapsulate the backbones of carbonized melamine foams; meanwhile, numerous hybrid CoNiP/CoNi nanoparticles are dispersedly attached to the carbon matrix. These special structures endow electrocatalysts with excellent HER and OER performances. Their overpotentials of 224 mV and 341 mV can carry out the current density of 10 mA/cm2, and the corresponding Tafel slopes are 85 mV/dec and 58 mV/dec. Moreover, this electrocatalyst has good durability in the long term electrolysis of HER and OER. In the end, the role of each component in the HER and OER processes has been revealed. Well-dispersed nanoparticles function as the main roles owing to their rich active sites and desirable electronic structures. Graphene nanosheets not only provide good substrates for nanoparticles but also hinder the shrinkage of carbonized melamine foams. Besides, 3D carbon foams inserted with plentiful graphene nanosheets could construct interconnected conductive networks and hierarchical porous structures, promoting electron-transfer kinetics and enhancing mass-transfer efficiency. Therefore, partially doping P atoms can largely enhance the electrocatalytic performances of bimetal CoNi, and the conjugation of 2D graphene nanosheets and 3D carbon foams would be one promising candidate for electrocatalytic support. This work may deliver valuable guidance for exploiting high-performance electrocatalysts.

First principles calculation study of single transition metal atom grafted Au25 as efficient electrocatalysts for OER and ORR

The method of grafting metal atoms by ligands can construct 'grafted single-atom catalysts' with good catalytic activity without destroying the cluster structure. In this study, the catalytic performance of Fe2+, Co2+ and Ni2+ grafted Au25(SR)18 cluster through l-cysteine ligand as bridging ligand (denoted as Au25-nCys-M, where n is the number of grafted Cys-ligand) in OER and ORR was investigated by density functional theory (DFT) simulations. A volcanic diagram between the overpotential of OER and ORR and the adsorption free energy of intermediates on Au25–nCys-M was determined, which showed that the adsorption strength of oxygenated intermediates can be adjusted by the grafting method and the number of bridging ligands, thus affecting the catalytic performance. Among three kinds of metal ions, the grafted Ni2+single atom catalysts showed excellent bi-functional OER and ORR activities. In particular, the Au25–1Cys-Ni2+ (n = 1) had the lowest overpotentials of 0.48 and 0.27 V for OER and ORR. Through in-depth analysis, we found that the spin magnetic moments of metal cations can be used as the descriptor of the catalytic performance of the grafted single atom catalyst. The excellent catalytic performance of Au25–nCys-Ni2+was originated from the smaller spin magnetic moment of Ni2+. These findings provided new idea for the preparation of nanocomposites with excellent OER and ORR catalytic performance.

Metal-organic framework derived core-shell nanoparticles as high performance bifunctional electrocatalysts for HER and OER

Development of an affordable, stable, and efficient electrocatalyst using nonprecious material to generate green H2 and O2 is still a challenging research problem. This research demonstrates the development of an efficient bifunctional electrocatalyst for HER as well as OER. Self-sacrificial nickel-based MOF acted as a precursor in facile pyrolysis carried out at 600, 700, and 800 °C temperatures to yield three bifunctional electrocatalysts viz Ni@NCS-600, Ni@NCS-700, and Ni@NCS-800, respectively. A blend of metallic Ni-nanoparticles and heteroatoms (N, S, & O) doped graphitic matrix has shown a synergistic effect for efficient electrocatalysis. The facile transformation of Ni-MOF into core-shell structure imparts stability to metal electrocatalyst by preventing direct exposure to the electrolytes during water splitting. After systematic characterization by various analytical techniques, their electrocatalytic performances were evaluated for OER and HER in alkaline and acidic medium, respectively. Bifunctional electrocatalytic activity of Ni@NCS-800 was found to be highly efficient, and comparable to precious state-of-the-art catalysts (RuO2 and Pt/C). Ni@NCS-800 exhibits extremely low overpotential, which needs only 330 mV and 366 mV to reach 10 mAcm−2 current density in OER and HER, respectively. The Tafel slope has been derived from the EIS also, imparting the alternating current. Thereby, a superior electrokinetic activity of Ni@NCS-800 has been observed, due to the elimination of non-faradaic current, with a Tafel slope of 32 mV/dec. The stability was evaluated by potentiostatic and potentiodynamic techniques. Therefore, this study explores a suitable pathway for the fabrication of simple, nonprecious, stable, yet catalytically efficient material for HER and OER activity.

Manganese-doped cobalt spinel oxide as bifunctional oxygen electrocatalyst toward high-stable rechargeable Zn-air battery

High-performance and low-cost bifunctional electrocatalysts for ORR and OER are urgently required for rechargeable Zn-air batteries. Herein, a series of Mn-doped Co3O4 nanoparticles grown on carbon nanotubes (Mn-Co3O4@CNTs) bifunctional electrocatalysts are designed. Owing to the moderate doped Mn atoms, the Mn-Co3O4 heightens ORR activity via the synergistic effect between Co and Mn atoms, and more Co3+ active sites are exposed on the surface of Mn-Co3O4 to enhance the OER rate. As a result, the 40% Mn-doped Mn-Co3O4@CNTs electrocatalyst exhibits higher ORR (E1/2 = 0.84 V) and OER (η10 = 356 mV at 10 mA cm−2) performance. More significantly, the Mn-Co3O4@CNTs equipped with rechargeable ZAB displays a high power density of 116 mW cm−2, a low charge-discharge voltage gap of 0.94 V at 10 mA cm−2, and superior cycling stability of over 425 h and 1200 cycles, being much more outperforming than Pt- and Ru-based ZABs.

Rational design of MOFs-derived Co-Ru species embedded N-doped carbon/carbon matrix for highly-efficient and multifunctional electrocatalysis

Developing efficient and durable multifunctional electrocatalysts for HER, OER and ORR is a pressing challenge for the practical application of water splitting and regenerative Zn-air batteries. Herein, core–shell Co-Ru nanocomposites embedded in N-doped carbon matrix (CoRu@NC) is fabricated for highly active HER by using hexamethylenetetramine (HMT) based MOFs as precursor, which is further developed into bimetallic oxide encapsulated into carbon (CoRuOx@C) as multifunctional catalysts for OER and ORR. Taking advantage of synergistic effects between two species and the porous core–shell structure, the resulting water electrolyzer (CoRu@NC||CoRuOx@C) displays excellent performance in pH-universal electrolyte, surpassing Pt/C||RuO2 counterpart and most reported electrocatalysts. More attractively, the CoRuOx@C exhibites significantly high-activity for ORR in 0.1 M KOH, possessing a half-wave potential of 0.864 V (23 mV higher than that of Pt/C benchmark) with excellent durability. This work provides a feasible strategy to construct multifunctional catalysts for efficient water splitting and Zn-air batteries.

The critical role of A, B-site cations and oxygen vacancies on the OER electrocatalytic performances of Bi0.15Sr0.85Co1−xFexO3−δ (0.2 ≤ x ≤ 1) perovskites in alkaline media

Development of perovskite-type electrocatalysts with high activity, excellent durability and affordable cost provides a promising solution to promote commercialization of clean energy technologies. Here we prepared Bi0.15Sr0.85Co1−xFexO3−δ (x = 0.2, 0.4, 0.6, 0.8, 1) perovskites by the conventional solid-state reaction route, and investigated their OER electrocatalytic activity and durability in 0.1 M KOH solution to reveal the critical role of A, B-site cations and oxygen vacancies. Results show the OER activity decreases with increasing x. The optimum composition, BiSC0.8F0.2, presents impressive electrocatalytic performances with low overpotential (330 mV on rotation disk electrode, and 283 mV on carbon paper electrode at 10 mA/cm2) and excellent long-time durability showing a small increase in the overpotential of 17 mV in 167.5 h. Comprehensive analysis and discussion on the bulk and surface properties reveal the critical role of A, B-site cations and oxygen vacancies on OER, and interrelations of Co2+ fraction, oxygen non-stoichiometry and the OER overpotential have been established. Most importantly, a highly A-site deficient surface layer is found on the as-synthesized perovskite, which facilitate OER by exposing more active B-site cations. This work not only reports a promising OER electrocatalyst with high activity and superior durability, but also provides perspectives on relational design for highly efficient and stable perovskite electrocatalysts for OER using solid-state reaction method.

Bimetallic-ZIFs derived quaternary amorphous LDHs decorated with crystalline Ag nanoparticles for highly efficient oxygen evolution reaction

Amorphous LDHs materials have been considered promising electrocatalysts for OER since their abundant coordination sites but still undergo poor stability. It is an efficient strategy to rationally architect amorphous/crystalline hybrid nanostructures on the ZIFs-derived amorphous LDH counterparts. Herein, we provide a facile two-step method to fabricate crystalline Ag NPs decorated amorphous QLDHs (Ag/QLDHs) nanosheet arrays on the Ni foam through ions exchange and spontaneous redox reaction. Based on the multi-metal synergetic effects (Co, Zn, Fe, Ni) and regulation of Ag nanoparticles (NPs), the as-formed Ag/QLDHs with heterogeneously hierarchal structures exhibit excellent OER performance with a low overpotential of 216 and 247 mV under 10 and 100 mA cm−2 in 1 M KOH, respectively, together with highly structural robustness. Through using the in situ-Raman spectroscopy, we reveal that the Ag NPs play the important role in enhancing the oxidation state of Ni and Fe species in Ag/QLDHs, which facilitates the generation of active MOx(OH)y at a much lower potential. The synthesized approach proposed in this work will supply a promising pathway for constructing amorphous/crystalline hybrid structures applied to alkaline water oxidation.

Tailoring structural properties of carbon via implanting optimal co nanoparticles in n‐rich carbon cages toward high‐efficiency oxygen electrocatalysis for rechargeable zn‐air batteries

AbstractRational construction of carbon‐based materials with high‐efficiency bifunctionality and low cost as the substitute of precious metal catalyst shows a highly practical value for rechargeable Zn‐air batteries (ZABs) yet it still remains challenging. Herein, this study employs a simple mixing‐calcination strategy to fabricate a high‐performance bifunctional composite catalyst composed of N‐doped graphitic carbon encapsulating Co nanoparticles (Co@NrC). Benefiting from the core‐shell architectural and compositional advantages of favorable electronic configuration, more exposed active sites, sufficient electric conductivity, rich defects, and excellent charge transport, the optimal Co@NrC hybrid (Co@NrC‐0.3) presents outstanding catalytic activity and stability toward oxygen‐related electrochemical reactions (oxygen reduction and evolution reactions, i.e., ORR and OER), with a low potential gap of 0.766 V. Besides, the rechargeable liquid ZAB assembled with this hybrid electrocatalyst delivers a high peak power density of 168 mW cm−2, a small initial discharge‐charge potential gap of 0.45 V at 10 mA cm−2, and a good rate performance. Furthermore, a relatively large power density of 108 mW cm−2 is also obtained with the Co@NrC‐0.3‐based flexible solid‐state ZAB, which can well power LED lights. Such work offers insights in developing excellent bifunctional electrocatalysts for both OER and ORR and highlights their potential applications in metal‐air batteries and other energy‐conversion/storage devices.

Interfacial Fe−O−Ni−O−Fe Bonding Regulates the Active Ni Sites of Ni‐MOFs via Iron Doping and Decorating with FeOOH for Super‐Efficient Oxygen Evolution

AbstractThe integration of Fe dopant and interfacial FeOOH into Ni‐MOFs [Fe‐doped‐(Ni‐MOFs)/FeOOH] to construct Fe−O−Ni−O−Fe bonding is demonstrated and the origin of remarkable electrocatalytic performance of Ni‐MOFs is elucidated. X‐ray absorption/photoelectron spectroscopy and theoretical calculation results indicate that Fe‐O−Ni−O−Fe bonding can facilitate the distorted coordinated structure of the Ni site with a short nickel–oxygen bond and low coordination number, and can promote the redistribution of Ni/Fe charge density to efficiently regulate the adsorption behavior of key intermediates with a near‐optimal d‐band center. Here the Fe‐doped‐(Ni‐MOFs)/FeOOH with interfacial Fe−O−Ni−O−Fe bonding shows superior catalytic performance for OER with a low overpotential of 210 mV at 15 mA cm−2 and excellent stability with ≈3 % attenuation after a 120 h cycle test. This study provides a novel strategy to design high‐performance Ni/Fe‐based electrocatalysts for OER in alkaline media.

Interfacial Fe-O-Ni-O-Fe Bonding Regulates the Active Ni Sites of Ni-MOFs via Iron Doping and Decorating with FeOOH for Super-Efficient Oxygen Evolution.

The integration of Fe dopant and interfacial FeOOH into Ni-MOFs [Fe-doped-(Ni-MOFs)/FeOOH] to construct Fe-O-Ni-O-Fe bonding is demonstrated and the origin of remarkable electrocatalytic performance of Ni-MOFs is elucidated. X-ray absorption/photoelectron spectroscopy and theoretical calculation results indicate that Fe-O-Ni-O-Fe bonding can facilitate the distorted coordinated structure of the Ni site with a short nickel-oxygen bond and low coordination number, and can promote the redistribution of Ni/Fe charge density to efficiently regulate the adsorption behavior of key intermediates with a near-optimal d-band center. Here the Fe-doped-(Ni-MOFs)/FeOOH with interfacial Fe-O-Ni-O-Fe bonding shows superior catalytic performance for OER with a low overpotential of 210 mV at 15 mA cm-2 and excellent stability with ≈3 % attenuation after a 120 h cycle test. This study provides a novel strategy to design high-performance Ni/Fe-based electrocatalysts for OER in alkaline media.

Boosting oxygen electrode kinetics by addition of cost-effective transition metals (Ni, Fe, Cu) to platinum on graphene nanoplatelets

Pt and Pt-M (M = Ni, Fe, Cu) nanoparticles supported on graphene nanoplatelets (GNPs) were synthesized by simultaneous supercritical carbon dioxide deposition method. Morphology analysis by TEM revealed the formation of metal nanoparticles of 2–3 nm size uniformly distributed over GNPs, while XPS was used to determine their oxidation states. Four materials were tested as electrocatalysts for ORR and OER in unitized regenerative fuel cells and rechargeable metal-air batteries. PtFe/GNPs exhibited favorable ORR kinetics in terms of the highest diffusion-limited current density, the lowest Tafel slope, and a high number of exchanged electrons (n = 3.66), which might be attributed to its high double-layer capacitance and, thus, high electrochemically active surface area. Furthermore, this material performance was comparable to that of commercial Pt/C electrocatalyst containing double the amount of Pt. The same material showed the best performance toward OER as evidenced by the highest current density, the lowest value of exchange current density, and overpotential to reach a current density of 10 mA cm-2, as well as the lowest Tafel slope.

N-doped hollow porous carbon spheres@Co Cu Fe alloy nanospheres as novel non-precious metal electrocatalysts for HER and OER

In this work, a string of different proportion trimetallic loaded the N-doped hollow porous carbon nanospheres (N-HPCS@Co Cu Fe NSs) were successfully crafted by a simple and economical method. Herein, the hollow-carbon structure was formed by etching carbon nanospheres. Moreover, owing to the presence of the PDA and P123, high dispersed nano spheres with mesopores were obtained. By this way, the catalyst can expose unique internal cavity and short transport path. Meanwhile, trimetal-based metal-organic frameworks (MOFs) Co Cu Fe alloy nano spheres (Co Cu Fe NSs) are first prepared. Creatively, PDA acts as the carbon resource, nitrogen resource and metal grafting agent simultaneously. Through a series of tests, N-HPCS@Co1 Cu1 Fe NSs has the best electrocatalytic performance and durable stability. This work highlights the current advances of hollow porous carbon structure, trimetallic active sites and N-doping, as well as, endow high electrocatalytic activity and durability for HER and OER.

Boron nitride-based electrocatalysts for HER, OER, and ORR: A mini-review

Boron nitride-based electrocatalysts for HER, OER, and ORR: A mini-review

Inside Back Cover: Hydrogen production coupled with water and organic oxidation based on layered double hydroxides (EXP2 3/2021)

In the cover of article number 20210050, Mingfei Shao and colleagues present an overview of latest progress of hydrogen production from perspectives of designing efficient LDHs-based electrocatalysts for OER and electrochemical hydrogen-evolution coupled with alternative oxidation (EHCO). The challenges and prospective in this promising research field were concluded, hoping to provide inspiration for the development of low-cost hydrogen production technology.

Efficient OER nanocomposite electrocatalysts based on Ni and/or Co supported on MoSe2 nanoribbons and MoS2 nanosheets

It is well known that the benchmark electrocatalysts for OER in alkaline solution are RuO2 and IrO2; however, the high cost, scarcity, and instability of these metal oxides impede their ample use in OER processes, and this has fueled the search for cheap Earth-abundant elements which are equally efficient for application as electrocatalysts in OER. The present work reports the use of hydrothermal and calcination methods for the synthesis of nanocomposites made up of Ni and/or Co salts and urea in combination with MoSe2 and MoS2 and their application as efficient and stable electrocatalysts for OER in alkaline solution. The NiCoMoSe, NiCoMo, CoMoSeS, and CoMo nanocomposites constructed in the present study presented high OER electrocatalytic activity and stability mainly as a result of the following: the combination of N atoms bonded to Ni and/or Co (and Mo); the electrons released from the oxidation of Co from the 2+ to 3+state, Ni oxidation from the 2+ to 3+state, and Mo oxidation from the 4+ to 6+state; and the metal oxides (CoMoO4, NiCo2O4, Co2Mo3O8, and Co3O4) supported on MoS2 nanosheets and MoSe2 nanoribbons which contributed to a decrease in charge transfer resistance, apart from keeping the ECSA values relatively low.

Co-modified Ni/N-doped carbon as electrocatalysts for HER and OER

Co-modified Ni/N-doped carbon as electrocatalysts for HER and OER

Facile synthesis of porous CoxFe1−xF2 microcubes derived from metal-organic frameworks for ultra-stable electrochemical oxygen evolution reaction

Fabricating efficient and low-cost noble-metal free electrocatalysts for the oxygen evolution reaction has been considered as a top priority for developing renewable energy devices. In this work, a series of CoxFe1−xF2 (x = 0.33, 0.50, 0.66, 0.75 and 0.80) with porous structure were prepared through low-temperature fluorination of MOFs precursors with controlled molar ratios of cobalt and iron and used as electrocatalysts for OER. Significantly, the Co0.66Fe0.33F2 exhibited the most excellent OER catalytic performance with a low overpotential of 260 mV at 10 mA cm−2 and a small Tafel slope of 54 mV dec−1. Moreover, it has an ultra-long durability of 50 h at current densities of 10 mA cm−2 and 50 mA cm−2, which is superior to most of non-noble metal and RuO2 electrocatalysts. The outstanding performance could be addressed to the porous structure and synergistic effect of CoF2 and FeF2 and in situ formed oxides, which could increase the active sites for electrochemical reactions and promote the proton transport and ion diffusion during the reaction process. This work proposes a brief and efficient way to design three-dimensional porous structure electrocatalyst.

Core-Shell-Structured Prussian Blue Analogues Ternary Metal Phosphides as Efficient Bifunctional Electrocatalysts for OER and HER.

Electrochemical water splitting is regarded as the most potential sustainable hydrogen production technology. However, the slow reaction kinetics and high overpotential of this process will result in low energy conversion efficiency. Therefore, it is of great practical value to research low-cost, efficient, and stable transition-metal-based bifunctional electrocatalysts. Herein, Fe-Co Prussian blue analogue (PBA) was coated with Ni-Co PBA to prepare the trimetallic PBA precursor, and the trimetallic phosphate (Fe-Co-Ni-P-1) has been prepared via the low-temperature phosphating process. The effects of metal ratios, the amount of sodium hypophosphite, and phosphating temperature on the catalytic performances were studied. When Fe-Co-Ni-P-1 was used as an electrocatalyst, the overpotential of oxygen evolution reaction and hydrogen evolution reaction was 247 and 215 mV, respectively, at a current density of 10 mA cm-2. At the same time, Fe-Co-Ni-P-1 showed faster kinetics and better long-term stability in the catalytic process. The catalytic performances of unary metal, binary metal, and ternary metal phosphides, oxides, and sulfides were systematically studied. It is demonstrated that the ternary metal phosphide Fe-Co-Ni-P-1 manifests the best catalytic performance, which is mainly attributed to the monodisperse core-shell structure, low resistance, large electrochemical active area, and the synergistic effect among metals.