Bifunctional Electrocatalytic Activity Research Articles

The Trade-Off Relationship between Particle Proximity Effect and Low-Pt Loading to Optimize Oxygen Reduction and Methanol Oxidation Reaction Activity

Pt-based electrocatalysts have long been considered as the most effective oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) catalysts due to their excellent intrinsic activity. For supported catalysts, Pt loading, particle size, interparticle distance (ipd), and interaction with support are identified as key contributors for high activity and selectivity. The proximity effect is a relatively new topic in catalysis research. There is a contradiction between the traditional view which induces the electronic interaction to reduce the activity and the new view which causes the electrical double-layer overlap of adjacent nanoclusters, changes the potential distribution and improves the specific activity. [1, 2]To this end, we have developed the nitrogen-doped graphite-like carbon sheets supporting low-Pt loading (Pt@N-GC) with uniform sizes and controllable ipd, and disentangled the main effect of ipd on ORR activity/selectivity and MOR activity/CO tolerance. Combining electrochemical tests and the trade-off mechanism between proximity effect and low-Pt loading, the following trends were obtained:1) 10.0 wt% Pt@N-GC with highest Pt loading and lowest ipd inhibits 2e- ORR by strong adsorption and reabsorption of *OOH due to the presence of closer Pt sites, and improves 4e- ORR selectivity. However, the mass activity/specific activity reached the maximum under the optimal low-Pt loading of 5.0 wt%.2) Similarly, 10.0 wt% Pt@N-GC weakened the adsorption of the -OH group of oxidized COads intermediates, led to the strong adsorption of COads on the catalyst surface, inactivated of Pt sites and reduced the CO resistance. Considering the need to improve CO tolerance while increasing MOR activity, the 5.0 wt% low-Pt loading catalyst exhibiting the best MOR performance under the optimal ipd.3) Benefiting by the synergistic effect of Pt nanoparticles and N-GC support, all Pt@N-GCs exhibit bifunctional electrocatalytic activity and durability.We attribute these findings to the underlying mechanism trade-off between the particle proximity effect and low-Pt loading under the uniform particle size and controlled ipd (Figure. 1). We believe the proximity effect has positive and negative effects, how to maximize the advantages of proximity effect can provide valuable guidance for the design and optimization of low-Pt loading bifunctional electrocatalysts in the future.[1] M. Nesselberger, M. Roefzaad, R.F. Hamou, P.U. Biedermann, F.F. Schweinberger, S. Kunz, K. Schloegl, G.K. Wiberg, S. Ashton, U. Heiz, K.J. Mayrhofer, M. Arenz, Nat. Mater., 12 (2013) 919-924.[2] M. Watanabe, H. Sei, P. Stonehart, J. Eelectroanal. Chem., 261 (1989) 375-387. Figure 1. The trade-off mechanism analysis between proximity effect and low-Pt loading. Figure 1

Metal(Pt, Pd)-Perovskite Oxide(Ba0.5Sr0.5Co0.8Fe0.2O3-δ) Hybrid Material As a Bifunctional Electrocatalyst for Lithium-Air Battery

The rapid depletion of fossil fuel resources and growing concerns over climate change have made the development of next-generation batteries a top priority. Among these, Li-O2 batteries have attracted significant interest due to their potential for much higher gravimetric energy storage density compared to other chemical batteries. However, efficient and cost-effective catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are critical for the efficient functioning of these batteries.In recent years, complex perovskite oxides, such as Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), have been identified as promising candidates for bifunctional catalysts due to their defective structures and excellent oxygen mobility. However, while BSCF exhibits high OER activity, its ORR performance is poor. To address this issue, researchers have turned to metal-oxide composite catalysts, where nanosized metals are deposited on the surface of perovskite oxides, to increase activity and stability towards ORR due to the synergistic effect between metal and oxide support.In this study, we report the development of bifunctional electrocatalysts with highly electrocatalytic activity for ORR and OER. We used a simple wet-chemical processing technique to deposit metal catalysts with superior ORR activity on perovskite oxide-based catalysts with high OER activity. The direct deposition method is an effective way to create a good distribution of metal catalysts, intimate contact between metal catalysts and BSCF perovskite oxide, which may contribute to the creation of a synergistic effect between them. Our results showed that the metal catalysts deposited on perovskite oxides of Pd@BSCF and Pt@BSCF exhibited better ORR activity than others and higher OER activity than the perovskite oxides alone, resulting in much-enhanced bifunctionality through a synergistic effect between the metal catalysts and perovskite oxides.We further investigated the enhanced bifunctional electrocatalytic activity of the metal catalysts deposited perovskite oxides for Li-O2 batteries. The assembled Li-O2 batteries with Pd@BSCF cathode demonstrated lower discharge/charge overpotential (0.8 V at the cutoff capacity of 500 mAh gcat -1) and improved cycling stability (over 70 cycles), indicating the effectiveness of our approach in enhancing the bifunctional activities of ORR and OER for application in electrochemical energy storage and conversion systems. The encouraging results obtained from this study might have been attributed to two mechanisms, namely, the synergistic effect of electronic transfer and RDS/spillover. Our study suggests that the deposition of metal catalysts on the surface of perovskite oxides (Pd@BSCF and Pt@BSCF) is an effective approach to enhance bifunctional activities of ORR and OER, making it a promising strategy for the development of next-generation batteries. Figure 1

Porous freestanding FeCoMnNiSe2 medium-entropy bifunctional electrocatalyst for oxygen and hydrogen evolution reactions in alkaline medium

Efficient bifunctional electrocatalysts towards oxygen and hydrogen evolution reactions (OER/HER) in water splitting is highly desirable for fuel cells and sustainable energy storage. Herein, one novel three-dimensional medium-entropy freestanding flower-like OER/HER bifunctional FeCoMnNi diselenide (FeCoMnNiSe2) electrocatalyst is fabricated by a facile hydrothermal and selenizing method. Benefiting from three-dimensional porous frame structure, lattice distortion and synergy effects, the as-prepared FeCoMnNiSe2 presents superior OER/HER bifunctional electrocatalytic activities with the quite low overpotentials of 223.1 mV for OER and 142.2 mV for HER at 100 mA cm−2 in 1.0 M KOH. More impressively, when employed for water splitting in a full cell, this bifunctional FeCoMnNiSe2 only requires ca. 1.42 V to drive the current densities of 100 mA cm−2 and displays outstanding stability for more than 60 h in 1.0 M KOH at 10, 50, 80 and 100 mA cm−2, surpassing almost all of reported advanced non-noble metal-containing OER/HER bifunctional electrocatalysts, and showing a promising potential application for industrial-scale water splitting.

Construction of Dual-atom catalysts on MoTe2 monolayer to achieve high-efficiency OER/ORR performance

Developing efficient, economical and environmentally friendly multifunctional electrocatalysts is a prerequisite for developing renewable energy conversion and storage technologies. Dual-atom catalysts have significant catalytic performance compared to monoatomic catalysts due to the larger metal loading and synergistic effects between metal atoms, and the reduction of overpotentials and increase of the reaction rate are the keys to obtaining high-performance OER/ORR bifunctional electrocatalysts, as determined by the electrocatalytic thermodynamics and kinetics of electrocatalysis. This work investigates efficient electrocatalysts with bifunctional catalytic activity for OER/ORR. Modifying the MoTe2 material by doping with transition metal atoms shows that the catalysts exhibit better electrochemical stability due to higher solvation potentials. The Pd2@MoTe2 catalysts were screened for bifunctional electrocatalysts due to the change in the local chemical environments. The Pd2@MoTe2 catalysts have excellent bifunctional electrocatalytic activity with overpotentials for OER and ORR of 0.23 and 0.21 V. The results show it can compete with and outperform the currently developed catalysts. This excellent catalytic activity can be attributed to the change in the coordination environment around the modified material, resulting in a change in electronic properties. This effectively ensures excellent electrical conductivity and electron transfer to modulate the strength of adsorbate interactions and optimize the catalytic performance. This work provides new ideas for understanding and optimizing the active center of bifunctional catalysts and new strategies for designing high-performance multifunctional electrocatalysts for metal-air batteries.

Lanthanum strontium cobaltite-based perovskite as an electrocatalyst for zinc-air battery application

Developing a low-cost and highly efficient electrocatalyst for bifunctional oxygen electrocatalytic activity is crucial in the field of energy conversion and storage devices. In this study, we employed a doping strategy to finely tune the electronic structure of lanthanum strontium cobaltite-based perovskite. Furthermore, we introduce Mn, Ni, and Cu cations as dopants at the B-site of lanthanum strontium cobaltite, La0.5Sr0.5CoO3 (LSCO), to investigate oxygen electrocatalytic activity in alkaline electrolytes. Among the electrocatalysts we synthesized, La0.5Sr0.5Co0.8Ni0.2O3 (LSCNiO) exhibited the lowest OER overpotential (ηj=10) of 429 mV in 0.1 M KOH, surpassing LSCO by 71 mV and LCO by 204 mV, respectively. Additionally, LSCNiO demonstrated a positive potential of 0.68 V @ 1 mA cm−2 for ORR, which is 50 mV less for LSCO catalyst. The improved electrocatalytic activity was investigated using spectroscopic techniques, confirming the presence of oxygen vacancies and an elevated Co oxidation state. The synergistic interplay between Co and Ni cations enhanced the hybridization between Co/Ni 3d and O 2p bands, reducing energy barriers and improving oxygen reaction kinetics. Finally, LSCNiO oxide with a bifunctional index (ΔE) of 1.08 V is tested for zinc-air battery (ZAB) applications.

Bifunctional Electrocatalytic Activity of Two-Dimensional Metallophthalocyanine-Based Metal–Organic-Frameworks for Overall Water Splitting: A DFT Study

Bifunctional Electrocatalytic Activity of Two-Dimensional Metallophthalocyanine-Based Metal–Organic-Frameworks for Overall Water Splitting: A DFT Study

Heteroatom-doped carbon attached to ultra-fine Fe-NiCoP as high-performance oxygen electrocatalyst for Zn-air batteries

The construction of efficient and durable electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) remains a challenge for rechargeable Zn-air batteries (ZABs). Bimetallic phosphide (NiCoP) holds considerable promise as a bifunctional catalyst. Here, an efficient NiCoP-based bifunctional electrocatalyst was fabricated using PCN-222-assembled organophosphorus complexes, specifically 1,1-bis(diphenylphosphine)ferrocene (DPPF). These DPPF complexes serve as sources of phosphorus and metals, undergoing in-situ conversion into Fe-doped NiCoP nanoparticles (Fe-NiCoP) while simultaneously constructing a heteroatom-doped carbon matrix (NPC). The final catalytic structure, composed of ultra-fine Fe-NiCoP nanoparticles confined within the NPC, exhibits superior bifunctional electrocatalytic activity (with a ΔEgap of 0.69 V between OER and ORR) and exceptional stability. In-situ Raman spectroscopy and DFT calculations reveal that the high performance arises from the synergistic effect of Fe-NiCoP and NPC, where Fe-NiCoP triggers the catalytic activity of the attached NPC. The calculated active site is identified as the C atom near the N atom on the NPC, lowering the potential barrier for O-containing intermediate compounds and enhancing the catalytic performance. In addition, NPC protects the Fe-NiCoP core from oxidation during battery cycles, allowing ZABs equipped with this catalyst to achieve high power density and long-term cycling performance.

Nickel Phosphonate MOF Derived N-Doped Carbon-Coated Phosphorus-Vacancies-Rich Ni2 P Particles as Efficient Bifunctional Oxygen Electrocatalyst.

The design of non-noble metal bifunctional electrocatalysts with outstanding performance and remarkable stability for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the most essential issues to the realization of rechargeable zinc-air battery, and transition metal phosphides (TMPs) have emerged as robust candidates for oxygen electrocatalysts. Herein, N-doped carbon-coated phosphorus-vacancies-rich Ni2 P particles (Vp -Ni2 P@NC) is proposed via simple carbonization and following Ar plasma treatment from a single nickel phosphonate metal-organic framework (MOF) without extra phosphine and nitrogen sources. The facile and rapid plasma treatment can achieve phosphorus vacancies which could modulate the electronic structure to enhance the inherent active and electrical conductivity. Meanwhile, the pyridine-N and graphitized-N produced during calcination also could provide more active sites and increase the electrical conductivity. The resultant Vp -Ni2 P@NC catalyst shows excellent bifunctional electrocatalytic activity (OER/ORR) based on synergistic effect of introducing P vacancies into Ni2 P and N-doped carbon. Vp -Ni2 P@NC catalyst shows more advantageous ΔE value (0.70 V) compared to Pt/C+RuO2 (0.73 V) and most reported catalysts. Additionally, the zinc-air bbatterie (ZAB) employing Vp -Ni2 P@NC as air cathode shows excellent performance. The maximum power density of 203.48 mW cm-2 , the cycling stability of more than 150 h at 10 mA cm-2 .

Investigation of improved Bifunctional electrocatalytic HER and OER performances of Lanthanum Molybdate supported Graphene oxide composite in Acidic and Alkaline media

Developing low-cost and high-performance emergent bifunctional electrocatalysts (ECs) is crucial to catalyze the overall electrocatalytic water-splitting. In this work, Lanthanum Molybdate (LaM) in the graphene oxide (GO) surface to develop its electrocatalytic applications in various environments is designed and presented. LaM/GO ECs could enhance the HER catalytic efficiency with a less overpotential of −0.21 V and less Tafel slope value of 81 mV dec−1 at an optimum current density of 10 mA cm−2 on typical acid media. Also, the less Tafel slope of 186 mV dec−1 and less overpotential (0.56 V) for catalyzing OER in alkaline media signifies its bifunctional electrocatalytic HER and OER activity. Moreover, it could exhibit admirable durability after 5000 cycles in both alkaline and acidic media. The outstanding bifunctional electrochemical activity of LaM/GO might be accredited to the novel construction method and benefits of LaM not only facilitates electron transfer but also interacts with the GO layer surface to make a synergic catalytic effect and might offer a large electrochemical surface area. Hence, this present work could be prolonged to propose and fabricate these sequence composites with the advantage of bifunctional catalysts for practical water-splitting applications.

Synthesis of five polyoxometalate-based compounds by using hydrothermal one pot method: Structures, supercapacitor, electrocatalytic and photocatalytic properties

Five polyoxometalate (POM) based compounds were synthesized by traditional hydrothermal method, namely {Co2(HTPT)2(H2O)2[Mo8O27]} (1), {Co2(TPT)2(H2O)6}(β-Mo8O26)·4H2O (2), {Co2(TPT)2(H2O)2(δ-Mo8O26)}·2H2O (3), {M(TPT)2(H2O)2}(Mo6O19) (M = Co 4, Ni 5) (TPT = 3-(4-terahydro-2H-pyran-4-yl)methyl)-4H-1,2,4-triazol-3-yl)pyridine). Compounds 1−3 were obtained in one pot, realizing efficient utilization of the hydrothermal method. The photocatalytic activities of compounds 1, 2, 4 and 5 were evaluated by the degradation of Methylene blue (MB) and Rhodamine B (RhB) and the reduction of Cr6+. The effects of the amount of catalyst and the pH of the system on the photocatalytic performance were also studied. Experimental studies have shown that compounds 1 and 4 also exhibit good bifunctional electrocatalytic activity for reducing NO2−, Cr6+ and H2O2, but also oxidizing AA (Ascorbic Acid). Compounds 1, 2, 4 and 5 can serve as amperometric sensors for NO2− and Cr6+. Compounds 1 and 4 own properties of capacitor materia.

Adding Fe/dicyandiamide to Co-MOF to greatly improve its ORR/OER bifunctional electrocatalytic activity

Exploring efficient non-precious metal oxygen electrocatalysts for oxygen reduction/evolution reactions (ORR/OER) is of great importance in electrochemical energy conversion devices like metal-air battery. Among them, carbon-based composites derived from metal-organic framework (MOF) exhibit excellent catalytic performance in ORR/OER. In this paper, Co-MOF-67 was firstly prepared, and then mixed with FeCl3·6 H2O and dicyandiamide, followed by a one-step pyrolysis to obtain bamboo-like nitrogen-doped carbon nanotubes. For the samples, Fe and Co nanoparticles were encapsulated in the front end of the carbon nanotubes and the presence of new (n)-diamond carbon was unexpectedly found. The obtained catalyst (FeCo@CNTs-60) has an onset potential of 1.04 V for ORR in alkaline solution, which is close to the commercial Pt/C (40 wt% Pt) of 1.05 V. The onset potential of 1.02 V in quasi-neutral solution exceeds that of Pt/C of 0.99 V. In addition, FeCo@CNTs-60 exhibited a low potential difference of 0.81 V between OER and ORR potentials. The alkaline zinc-air batteries, fabricated with the sample as the electrocatalyst of air electrode, exhibit higher peak power density and stability than Pt/C, while the rechargeable batteries present superior cycling discharge/charge stability at 5 mA·cm−2 and 10 mA·cm−2. In particular, the battery with FeCo@CNTs-60 was conducted for continuous over 1300 h of ultra long-term cycle charging / discharging test at a current density of 5 mA·cm−2, and it reveals excellent stability with high voltage efficiency and also presents superior cycle charging / discharging stability after replacing the Zn plates and electrolyte.

Boosting bifunctional oxygen electrocatalysis with atomically dispersed Fe and Co dual-metal sites for flexible zinc-air batteries

Rechargeable zinc-air batteries (ZABs) hold enormous promise as energy conversion and storage system of the next generation. Here, through utilizing the Co/ZIF-8@F127 precursor and a coordinated strategy that includes ‘post-absorption’ and ‘dual-pyrolysis’, a Fe/CoNx-C possesses a hierarchical porous N-doped carbon with an ultrahigh specific area and rich defects to stabilize accessible dual metallic active sites. With a narrow potential gap of 0.71 V, the Fe/CoNx-C catalyst demonstrates excellent bifunctional electrocatalytic activity toward the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Noteworthily, scanning electrochemical microscopy (SECM) was used to visualize the local electrocatalytic ORR activity of CoNx-C and Fe/CoNx-C. For the applications of zinc-air batteries, the Fe/CoNx-C-based cathode provides a high peak power density of 134.97 mW cm−2 for aqueous ZABs. Moreover, quasi-solid-state ZABs (including flexible ZAB and cell ZAB)-based on Fe/CoNx-C as cathode catalyst demonstrate satisfying flexibility and durability. The theoretical calculation results further elucidate the synergistic effect that the engagement of Fe atoms in the electron transfer process of the FeN4@CoN4 system reduces the energy barrier of the rate-determining-step in ORR and OER, hence facilitating the reversible oxygen electrocatalytic kinetics.

Interface engineering of bifunctional nickel hydroxide/ nickel phosphide heterostructure for efficient intermittent hydrazine-assisted water splitting

Hydrazine oxidation reaction (HzOR) has been proposed to replace the sluggish oxygen evolution reaction (OER) for energy-saving hydrogen generation. However, the rational design of bifunctional electrocatalysts that can simultaneously accelerate HER/HzOR kinetics and the source of the hydrazine chemical substrate are still challenging. Herein, interfacial heterogeneous nickel hydroxide/nickel phosphide microstructures are in-situ grown on nickel foam (Ni(OH)2/Ni2P/NF) via a combined electrodeposition-phosphorization-electrodeposition strategy. After Ni(OH)2 modification, a charge redistribution is triggered between Ni(OH)2 and Ni2P, reducing the charge-transfer resistance and optimizing the adsorption energy of reaction intermediates. Ni(OH)2/Ni2P/NF thus yields an impressive bifunctional electrocatalytic activity for HER and HzOR with potentials of −72 and −14 mV at 10 mA cm−2, respectively. When using Ni(OH)2/Ni2P/NF as both electrodes, decreased cell voltage of 0.357 V is required to drive a current density of 100 mA cm−2 in 0.5 M hydrazine-containing alkaline electrolyte. Furthermore, an intermittent hydrazine-assisted water electrolysis system is proposed to make the combination of hydrazine sewage purification and energy-saving hydrogen production realistic.

Ni dispersed ultrathin carbon nanosheets as bi-functional oxygen electrocatalyst induced from graphite-like porous supramolecule

Excellent porosity and accessibility are key requirements during carbon-based materials design for energy conversion applications. Herein, a Ni-based porous supramolecular framework with graphite-like morphology (Ni-SOF) was rationally designed as a carbon precursor. Ultrathin carbon nanosheets dispersed with Ni nanoparticles and Ni-Nx sites (Ni@NiNx-N-C) were obtained via in-situ exfoliation during pyrolysis. Due to the hetero-porous structure succeeding from Ni-SOF, the Ni@NiNx-N-C catalyst showed outstanding bifunctional oxygen electrocatalytic activity with a narrow gap of 0.69 V between potential to deliver 10 mA cm−2 oxygen evolution and half-wave potential of oxygen reduction reaction, which even surpassed the Pt/C + IrO2 pair. Therefore, the corresponding zinc-air battery exhibited excellent power output and stability. The multiple Ni-based active sites, the unique 2D structure with a high graphitization degree and large specific surface area synergistically contributed to the excellent bifunctional electrocatalytic activity of Ni@NiNx-N-C. This work provided a novel viewpoint for the development of carbon-based electrocatalyst.

Conducting polymer-templated and nonnoble metal doped MoSe2 hybrids as bifunctional electrocatalysts for overall water splitting

Transition metal dichalcogenides (TMDs) are potential candidates for electrocatalytic applications due to their unique structures and intrinsic properties. In this work, the systematic synthesis of conducting polymer-templated and nonnoble metal-doped MoSe2 hybrids was carried out using a facile hydrothermal method. Integrating conductive polyaniline, as a conductive polymer, with MoSe2 nanosheets (MoSe2@PANI) as well as transition metal (Co, Ni or Fe) doping provided more active sites for both H+ and OH– adsorption, resulting in enhanced hydrogen and oxygen evolution performance. The Co-doped MoSe2@PANI hybrid catalyst exhibited enhanced bifunctional electrocatalytic activity for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in alkaline electrolytes, where Co-doping as well as polyaniline addition played key roles in boosting the HER/OER activity. As a result, the Co-doped MoSe2@PANI catalyst exhibited overpotentials of 196 mV and 385 mV at a current density of 10 mA cm−2 for the HER and OER, respectively. When Co-doped MoSe2@PANI was applied as a bifunctional electrocatalyst for overall water splitting, a potential of 1.82 V was needed to achieve a current density of 10 mA cm−2. Moreover, the Co-doped MoSe2@PANI catalyst displayed good stability for long-term cycling. This work provides new insight into the design of metal-doped TMD/conducting polymer-based materials for electrocatalytic applications, including water electrolysis.

Embedding Co6Mo6C2-Mo2C heterostructure nanoparticles in carbon nanofibers as highly efficient electrocatalysts for overall water splitting

In this study, carbon nanofibers (CNFs) embedding molybdenum carbide (Mo2C)/cobalt (Co)-molybdenum (Mo) bimetallic carbide heterostructure electrocatalysts (denoted as A-B/CNFs) were prepared via electrospinning and high-temperature carbonization. Owing to the synergistic interaction between Co6Mo6C2 and Mo2C components, the catalyst activity is improved. Furthermore, the rich mesoporous structure and electrical conductivity of CNFs, accelerate the reaction kinetics. As a result, the optimized Co6Mo6C2-Mo2C/CNFs-1 has excellent bifunctional electrocatalytic activity. With the current density of 10 mA cm−2, the hydrogen evolution reaction (HER) overpotential is only 94 mV, and the oxygen evolution reaction (OER) overpotential is 295 mV in an alkaline electrolyte. Building an alkaline electrolyzer with Co6Mo6C2-Mo2C/CNFs-1 as the anode and cathode electrodes requires a low cell voltage of only 1.66 V to achieve the current density of 10 mA cm−2, while maintaining ideal durability. This research offers a versatile and effective approach to creating bimetallic-based monolithic hydrolysis electrocatalysts.

Bimetallic co-doped CoP nanoflower arrays for efficient and stable overall water splitting

It is vital to develop efficient earth-abundant bifunctional electrocatalysts for water splitting to mitigate the global energy crisis and environmental pollution. Here, Mn and W dual transition metal co-doped CoP nanoflower arrays supported on nickel foam (Mn–W–CoP/NF) have been synthesized via the hydrothermal method and chemical vapor deposition. The unique nanoflower-type structure of Mn–W–CoP/NF facilitated high reactive-site exposure and efficient charge transfer. Consequently, Mn–W–CoP/NF exhibited excellent bifunctional electrocatalytic activity in alkaline electrolytes, with low overpotentials of 95.8 and 229.2 mV for the hydrogen evolution reaction and oxygen evolution reaction, respectively, at 10 mA cm−2. Furthermore, it could be used to construct a two-electrode water-splitting electrolyzer exhibiting stable water splitting at a low cell voltage (1.57 V) at 10 mA cm−2. This study could guide the design and development of efficient bifunctional electrocatalysts for large-scale water-splitting applications.

Ultralow Loading of Ru as a Bifunctional Catalyst for the Oxygen Electrode of Solid Oxide Cells.

The oxygen evolution reaction (OER) is a significant contributor to the cell overpotential in solid oxide electrolyzer cells (SOECs). Although noble metals such as Ru and Ir have been utilized as OER catalysts, their widespread application in SOECs is hindered by their high cost and limited availability. In this study, we present a highly effective approach to enhance air electrode performance and durability by depositing an ultrathin layer of metallic Ru, as thin as ∼7.5 Å, onto (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ (LSCF) using plasma-enhanced atomic layer deposition (PEALD). Our study suggests that the emergence of a perovskite, SrRuO3, resulting from the reaction between PEALD-based Ru and surface-segregated Sr species, plays a crucial role in suppressing Sr segregation and maintaining favorable oxygen desorption kinetics, which ultimately improves the OER durability. Further, the PEALD Ru coating on LSCF also reduces the resistance to the oxygen reduction reaction (ORR), highlighting the bifunctional electrocatalytic activities for reversible fuel cells. When the LSCF electrode of a test cell is decorated with ∼7.5 Å of the Ru overcoat, a current density of 656 mA cm-2 at 1.3 V in electrolysis mode and a peak power density of 803 mW cm-2 in fuel cell mode are demonstrated at 700 °C, corresponding to an enhancement of 49.1 and 31.9%, respectively, compared to the pristine cell.

N, S co-doped hollow carbon nanocages confined Fe, Co bimetallic sites for bifunctional oxygen electrocatalysis

Regulating pore architecture and electronic structure is of significance for improving oxygen electrocatalytic activity of M−N−C catalysts. Herein, N, S co-doped hollow carbon nanocages confined Fe, Co bimetallic sites (FeCo-NS-HNCs) are constructed through an efficient surface bridging strategy. The surface modifier of trithiocyanuric acid trisodium salt bridges Co doped ZIF-8 surface with Fe ions to promote the formation of Fe/Co-Nx sites. The synergistic coupling of metal sites and N, S co-doping manipulates the adsorption/desorption characteristics of M−Nx sites to optimize intrinsic activity. The Kirkendall effect constructs the hollow carbon nanocages, improving the accessibility of M−Nx sites. Benefiting from the ameliorated electronic structure and hollow porous architecture, FeCo-NS-HNCs displays excellent bifunctional oxygen electrocatalytic activity (ΔE = 0.655 V). The liquid and flexible Zn-air batteries of FeCo-NS-HNCs offer prominent power density and cycling stability. This work provides estimable insights into the structure design and activity regulation of M−N−C catalysts for Zn-air battery.

Boosting the bifunctional electrocatalytic activity of nitrogen-doped graphene by electronic effect of heterovalent ion substituted perovskite oxides

Sluggish reaction kinetics of carbon-based catalysts hinder their activity in oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which further impede commercialization of Zinc-air batteries. Here, a strategy of modifying the electronic structure of nitrogen-doped graphene (NG) through constructing it with cobalt (Co) substituted manganese-based perovskite oxides (LaMn1-xCoxO3) to accelerate its activity in OER and ORR is proposed. Co substitution is beneficial for donating electrons to oxygen-containing intermediates by inducing excessive negative charge on NG to improve kinetics in OER and ORR. The half-wave potential in ORR for LaMn0·6Co0·4O3@NG is 0.74 V, higher than that of LaMnO3@NG and LaCoO3@NG; the overpotential of LaMn0·6Co0·4O3@NG at 10 mA cm−2 is 314 mV for OER, smaller than that of LaMnO3@NG and LaCoO3@NG, supposing the superior electrochemical activity of composite catalyst with Co substitution in OER and ORR. This research offers a way in fabricating high efficient and cost-effective bifunctional electrocatalyst for Zinc-air batteries.