Bifunctional Cathode Catalyst Research Articles

Carbon-coated ZnS as a high-performance ORR/OER bifunctional cathode catalyst for zinc-air batteries

The commercial application of zinc-air batteries (ZABs) is hindered by the high cost and scarcity of precious metal catalysts. In this paper, we prepared high-performance ORR/OER bifunctional catalysts with a carbon-coated ZnS spherical structure (ZnS@C) through a hydrothermal method followed by a carbonization process. Characterized by their unique spherical coated pore structure, exhibit impressive electrocatalytic activity. Specifically, ZnS@C-2, produced by a secondary carbonization process demonstrates an ORR half-wave potential of 0.82 V (relative to RHE) and an OER overpotential of 377 mV at 10 mA cm−2. When employed in a ZAB, it achieves a maximum power density of 120.4 mW cm−2, a specific capacity of 836 mAh gZn−1, and maintains cycle stabilization for up to 165 h at 10 mA cm−2. The research results demonstrate that the unique carbon-coated internal porous structure not only significantly enhances the stability of the catalyst but also increases the number of active sites, thereby providing more abundant activation energy for the catalytic reaction and facilitating its efficient progress. This underscores the catalyst's excellent ORR and OER properties, suggesting promising practical application potential.

P-Block-metal bismuth embedded in N/P co-doped carbon nanorods for kinetics-enhanced rechargeable lithium-oxygen batteries

Rechargeable lithium-oxygen batteries (LOBs) are considered one of the most promising electrochemical energy storage devices due to their extremely high theoretical energy density. However, the slow redox kinetics of the oxygen cathode leads to low coulombic efficiency and poor cycling performance, which limits the development of high-performance LOBs. Herein, Bi@NPC heterostructure nanorods are designed with the assistance of p-block metal Bi and successfully synthesized as bifunctional cathode catalysts for LOBs. Experimental and theoretical calculations show that Bi@NPC electrode can significantly reduce overpotential during discharge/charge processes due to the easily tunable localized p-orbitals and resulting versatile electronic structures. Benefiting from p-orbital electrons regulation of Bi atoms, the Bi@NPC electrode exhibited superior specific capacity over 11852.6 mAh g−1, outstanding rate capabilities, and ultralong cycle stability over 83 cycles at 200 mA g−1 with the fixed capacity of 500 mAh g−1. This work reveals an efficient pathway to synthesize p-block metal-based catalysts for high-performance LOBs.

Engineering of MnTe/MnO Heterostructures with Interfacial Electric Field Modulation for Efficient and Durable Li–O2 Batteries

AbstractDesign and synthesis of highly active and robust bifunctional cathode catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are of vital significance for practical applications of lithium–oxygen (Li–O2) batteries. Herein, a built‐in electric field (BIEF) strategy is reported to fabricate MnTe/MnO heterostructures with a large work function difference (ΔΦ) as a bifunctional cathode catalyst in Li–O2 batteries. The MnTe/MnO heterostructures with nanosheets and microporous structures result in an abundance of exposed active sites and facilitate mass transfer. More importantly, the heterogeneous MnTe/MnO nano‐interface region provides a BIEF that can trigger interfacial charge redistribution, fine‐tune the adsorption energy of oxygen intermediates, and alter the morphology of discharge products to accelerate ORR/OER kinetics. Impressively, the fabricated Li–O2 batteries with MnTe/MnO cathode showcases exhibit excellent electrochemical performances, including low charging overpotential, a high specific capacity of 11930 mA h g−1, and good cycle stability over 350 cycles even with a fixed specific capacity of 500 mA h g−1 at a current density of 500 mA g−1. This work provides an avenue for the rational design of high performance heterostructure electrocatalysts toward practical applications for rechargeable Li–O2 batteries.

Bifunctional 0D carbon quantum dot cathode electrocatalyst coupled with atomic hydrogen and hydroxyl radicals for efficient removal of oxytetracycline hydrochloride

Efficient removal of antibiotics is difficult to achieve by conventional single-oxidation or reduction processes. Herein, a bifunctional cathodic electrocatalyst coupling atomic hydrogen (H*) reduction with hydroxyl radical (·OH) oxidation in an efficient electrocatalytic process was developed for the effective degradation of oxytetracycline hydrochloride (OTC). Pd particles were dispersed on B-doped carbon quantum dots to prepare a Pd-B-doped carbon quantum dots/titanium (Pd-BCQD/Ti) electrode as a bifunctional cathode catalyst. The electrode can simultaneously generate H* through the H2O/H+ reduction process, H2O2 through the oxygen reduction process, and then generate ·OH. H* performs nucleophilic hydrogenation reduction of OTC molecules, and ·OH performs electrophilic oxidation of the carbon skeleton, and both act synergistically with the active chlorine species (HClO) generated at the anode. The experimental results showed that the electrode achieved 90.50 % removal of OTC within 60 min. In addition, the Pd-BCQD/Ti electrode reduces energy consumption while increasing current efficiency. The degradation effect was more than 85.80 % in the pH range of 3∼9, indicating fairly stable catalytic activity over a wide pH range. The degradation efficiency was basically unchanged after ten cycles, and the reactivity was still high in the actual water. Intermediates were analyzed based on LC-MS to explore the degradation pathways of OTC. The toxicity of the intermediates generated during OTC degradation was predicted based on quantitative conformational relationships. This study provides a feasible strategy for the preparation of bifunctional catalysts based on zero-dimensional BCQD for efficient green antibiotic wastewater treatment.

Bifunctional Catalysts for CO2 Reduction and O2 Evolution: A Pivotal for Aqueous Rechargeable Zn-CO2 Batteries.

The quest for the advancement of green energy storage technologies and reduction of carbon footprint is determinedly rising toward carbon neutrality. Aqueous rechargeable Zn-CO2 batteries (ARZCBs) hold the great potential to encounter both the targets simultaneously, i.e., green energy storage and CO2 conversion to value-added chemicals/fuels. The major descriptor of ARZCBs efficiency is allied with the reactions occurring at cathode during discharging (CO2 reduction) and charging (O2 evolution) which own different fundamental mechanisms and hence mandate the employment of two different catalysts. This presents an overall complex and expensive battery system which requires a concrete solution, while the development and application of a bifunctional cathode catalyst toward both reactions could reduce the complexity and cost and thus can be a pivotal for ARZCBs. However, despite the increasing research interest and ongoing research, a systematic evaluation of bifunctional catalysts is rarely reported. In this review, the need of bifunctional cathode catalysts for ARZCBs and associated challenges with strategies have been critically assessed. A detailed progress examination and understanding toward designing of bifunctional catalyst for ARZCBs have been provided. This review will enlighten the future research approaching boosted performance of ARZCBs through the development of efficient bifunctional cathode catalysts.

Nickel-hydroxide decorated trimanganese-tetroxide nanorods supported on graphene as bifunctional electrocatalyst for metal–air batteries

Manganese oxide, such as Mn3O4, is one of promising material as electrocatalyst in air–cathode for metal–air battery due to low cost, high catalytic activity and good stability. Although pure Mn3O4 material exhibits excellent catalytic activity to ORR, it is severely limited by its intrinsically low conductivity and high over-potential toward OER. In this work, the hybrid materials of nickel-hydroxide-decorated nanorods of trimanganese-tetroxide supported on reduced-graphene have been prepared by one-step hydrothermal method. The composite materials are used as bifunctional cathode catalysts to ORR/OER, and investigated by the technologies of rotating disk electrode and metal–air batteries. The results indicate that the hybrid material of Mn-Ni/rGO use as catalyst in air–cathode for Al/Zn–air battery has good catalytic activity. Based on analysis of scanning electron microscope and X-ray photoelectron spectroscopy, the composite material shows good performance owing to the improvement of conductivity supported on graphene, more Mn4+ on the surface of hybrid material, the coexistence of Mn3+/Mn4+ redox couple, and the synergism between nickel-hydroxide and graphene.

Compositionally engineered NiCoLDH@rGO as bifunctional cathode catalyst for rechargeable Li-O2/Li-CO2 battery

Compositionally tuned nickel-cobalt layered double hydroxides (NCLDHs) and NCLDH@reduced graphene-oxide (NCLDH@rGO) were synthesized through a facile solvothermal synthesis route. The formation of the synthesized NCLDH and the NCLDH@rGO with the intercalated carbonate and nitrate anions, has been confirmed utilizing different characterization techniques. Microscopic results revealed the flaky morphology with thickness about 30 nm. Rotating ring disc electrode (RRDE) voltammetry was utilized to analyze the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and carbon dioxide reduction reaction (CO2RR) kinetics on each of the pristine (1:1), (2:1), (3:1) and (4:1) NCLDH catalysts and the NCLDH@rGO composites. The RRDE data revealed that the electrochemical activity towards ORR/OER/CO2RR could be largely increased by tuning mole ratio of the (Ni2+/Co3+) or the amount of the rGO in the NCLDH. It turned out that among the pristine electrocatalysts, the (1:1) NCLDH catalyst exhibited enhanced ORR/OER kinetics. While the NCLDH acted as a catalyst center, the rGO provided conductive network that facilitated passable overpotential with increased current density for the ORR/OER/ CO2RR. Better adsorption of O2 and CO2 on the NCLDH@rGO catalyst also contributed for the electrocatalytic activity. Consequently, the NCLDH@rGO composites as cathode catalyst for Li-O2 battery in the CR2032 prototype coin-cell exhibited a stable open circuit voltage (OCV). Among the NCLDH@rGO composites, the NCLDH with 15 wt.% rGO (NCRGO15) exhibited a high discharge capacity of 3616 mAh g−1 at 50 Ag−1 for the Li-O2 battery and a discharge capacity of 45 mAh g−1 at a current density of 100 Ag−1 for the CR2032 coin-type Li-CO2 battery. As a practical use, a commercial 2.8 V green LED bulb was lit continuously for about 20 h using the fabricated Li-O2 battery that consisted of lithium anode and (1:1) NCLDH@rGO15 wt.% (NCRGO15) air-breathing cathode.

Porous CN@MOF derived N, S-doped hierarchical framework carrying Co3Fe7/Fe0.8Co0.2S heterojunction: An efficient bifunctional cathode catalyst for Zn–air battery

The exploiting of bifunctional transition metal electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is of significance for the commercialization of rechargeable zinc-air batteries (ZABs). Herein, the N and S atoms-doped hierarchical carbon framework hosting the Co3Fe7/Fe0.8Co0.2S heterojunction is synthesized by employing porous g-C3N4 as framework and spacer, and FeCo-ZIF as metal source followed by sulfidation and pyrolysis. The detailed characterization confirms that the porous g-C3N4 plays a crucial role in improving the dispersion of metal nanoparticles. The obtained FeCo-Sx@NSC-900 catalysts exhibit layered accumulation configuration with uniformly distributed metal nanoparticles. Moreover, the typical carbon@metal nanoparticles and heterojunction structure can be observed from the HRTEM (High-Resolution Transmission Electron Microscopy) and HAADF-STEM (high-angle annular dark-field STEM) analysis results. The optimal FeCo-Sx@NSC-900 catalysts deliver exceptional ORR and OER performance with a potential difference between ORR and OER of merely 0.713 V, which is superior to the commercial Pt/C+RuO2 catalysts and other monometallic catalysts. Additionally, the ZAB assembled with the optimal FeCo-Sx@NSC-900 catalysts as cathode affords a good battery performance with high OCV (1.50 V), large power density (172 mW/cm2), good discharge stability, large specific capacity, and long-term charge/discharge stability (>300 cycles).

Synergistically S/N self-doped biochar as a green bifunctional cathode catalyst in electrochemical degradation of organic pollutant

Biomass-derived heteroatom self-doped cathode catalysts has attracted considerable interest for electrochemical advanced oxidation processes (EAOPs) due to its high performance and sustainable synthesis. Herein, we illustrated the morphological fates of waste leaf-derived graphitic carbon (WLGC) produced from waste ginkgo leaves via pyrolysis temperature regulation and used as bifunctional cathode catalyst for simultaneous H2O2 electrochemical generation and organic pollutant degradation, discovering S/N-self-doping shown to facilitate a synergistic effect on reactive oxygen species (ROS) generation. Under the optimum temperature of 800 °C, the WLGC exhibited a H2O2 selectivity of 94.2% and tetracycline removal of 99.3% within 60 min. Density functional theory calculations and in-situ Fourier transformed infrared spectroscopy verified that graphitic N was the critical site for H2O2 generation. While pyridinic N and thiophene S were the main active sites responsible for •OH generation, N vacancies were the active sites to produce 1O2 from O2. The performance of the novel cathode for tetracycline degradation remains well under a wide pH range (3–11), maintaining excellent stability in 10 cycles. It is also industrially applicable, achieving satisfactory performance treating in real water matrices. This system facilitates both radical and non-radical degradation, offering valuable advances in the preparation of cost-effective and sustainable electrocatalysts and hold strong potentials in metal-free EAOPs for organic pollutant degradation.

Heterostructure CoFe@(Co0.5Fe0.5)S@NCNT anchored on rice husk-based hierarchical porous carbon as a bifunctional cathode catalyst for Zn–air batteries

A bifunctional catalyst, characterized by its sea urchin-like morphology and multi-layer core–shell structure (CoFe@(Co0.5Fe0.5)S@NCNT), was synthesized within the restriction of RHPC' hierarchical pore structure.

Electrocatalytic Deep Dehalogenation and Mineralization of Florfenicol: Synergy of Atomic Hydrogen Reduction and Hydroxyl Radical Oxidation over Bifunctional Cathode Catalyst.

It is difficult to achieve deep dehalogenation or mineralization for halogenated antibiotics using traditional reduction or oxidation processes, posing the risk of microbial activity inhibition and bacterial resistance. Herein, an efficient electrocatalytic process coupling atomic hydrogen (H*) reduction with hydroxyl radical (•OH) oxidation on a bifunctional cathode catalyst is developed for the deep dehalogenation and mineralization of florfenicol (FLO). Atomically dispersed NiFe bimetallic catalyst on nitrogen-doped carbon as a bifunctional cathode catalyst can simultaneously generate H* and •OH through H2O/H+ reduction and O2 reduction, respectively. The H* performs nucleophilic hydro-dehalogenation, and the •OH performs electrophilic oxidization of the carbon skeleton. The experimental results and theoretical calculations indicate that reductive dehalogenation and oxidative mineralization processes can promote each other mutually, showing an effect of 1 + 1 > 2. 100% removal, 100% dechlorination, 70.8% defluorination, and 65.1% total organic carbon removal for FLO are achieved within 20 min (C0 = 20 mg·L-1, -0.5 V vs SCE, pH 7). The relative abundance of the FLO resistance gene can be significantly reduced in the subsequent biodegradation system. This study demonstrates that the synergy of reduction dehalogenation and oxidation degradation can achieve the deep removal of refractory halogenated organic contaminants.

Ni-Doped La0.6Sr0.4CoO3 Perovskite as an Efficient Electrocatalyst for Oxygen Reduction and Evolution Reactions in Alkaline Media

The Co-based perovskite La0.6Sr0.4CoO3 has received significant attention as a potential electrocatalyst for its oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) due to its abundance, facile synthesis, and high oxygen kinetics. However, research on the catalytic performance of Ni-doped La0.6Sr0.4Co1−xNixO3 as a bifunctional cathode catalyst for Zn-air batteries (ZABs) is still scarce. In this work, lanthanum strontium cobalt-based perovskite catalysts with various Ni contents (La0.6Sr0.4Co1−xNixO3, x = 0, 0.2, 0.5, and 0.8) were synthesized using a simple combustion method. The effects of Ni doping on the morphology, structure, surface oxygen-related species, and valence states of the transition metals of the perovskite were characterized. The electrochemical behaviors of the perovskite catalysts in both ORR and OER were also assessed. The characterization results revealed that proper Ni doping can decrease particle size, increase surface oxygen vacancies, and create mixed valence states of the transition metal and, thus, lead to improvement of the electrocatalytic activity of perovskite catalysts. Among the different perovskite compositions, La0.6Sr0.4Co0.8Ni0.2O3 exhibited the best ORR/OER activity, with a higher limiting current density, smaller Tafel slope, higher half-wave potential, lower overpotential, and lower potential difference than the other compositions. When La0.6Sr0.4Co0.8Ni0.2O3 was applied as the cathodic catalyst in a primary ZAB, it delivered a peak power density of 81 mW cm−2. Additionally, in rechargeable ZABs, the La0.6Sr0.4Co0.8Ni0.2O3 catalyst exhibited a lower voltage gap (0.94 V) and higher stability during charge–discharge cycling than the commonly used catalyst Pt/C. These results indicate that Ni-doped La0.6Sr0.4Co0.8Ni0.2O3 is a promising bifunctional electrocatalyst for ZAB.

Ba-doped LaCoO3 perovskite as novel bifunctional electrocatalyst for zinc–air batteries

Developing efficient non-noble metal bifunctional cathode catalysts to accelerate the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is still a major challenge for zinc–air batteries (ZABs). In the present study, a series of La1−xBaxCoO3 (x = 0, 0.05, 0.10, 0.15, 0.20) perovskite-type oxides were prepared via self-propagating high-temperature synthesis and evaluated as the bifunctional electrocatalytic activity for ZABs. Among the samples, La0.85Ba0.15CoO3 showed the best bifunctional catalytic activity, in which the Eonset of ORR at 0.1 mA cm−2 and the Ej of OER at 10 mA cm−2 in 0.1 M KOH solution were 0.829 and 1.685 V vs.RHE, respectively. Besides, the La0.85Ba0.15CoO3 catalyst was evaluated as an air electrode for ZABs, displaying a high power density of 116.2 mW cm−2 at the current density of 233.8 mA cm−2 and a stable charge–discharge voltage gap of 0.98 V after 1200 cycles, with superior cycling stability over 200 h. Characterization analysis revealed that the enhancement of bifunctional electrocatalytic activity was attributed to the larger specific surface area and increase in oxygen vacancy. Thus, the Ba-doped LaCoO3 material is a promising bifunctional electrocatalyst for ZABs.

Transformation of a new polyoxometalate into multi-metal active sites on ZIF-derived carbon nanotubes as bifunctional cathode catalyst and dendrite-free anode coating for Zn-air batteries

To improve the kinetics of the ORR/OER at the cathode and inhibit dendrite formation on the anode of a Zn-Air battery (ZAB), a new polyoxometalate (POM) with a basic structrual unit of [Zn{P4Mo6}2] was designed and converted to well-separated Zn/Mo2C catalytic sites on Co, N doped carbon nanotubes (Co-NCNTs) derived from ZIF-67. This conversion was achieved at a relatively low pyrolysis temperature of 600 °C, which circumvented the collapse of catalyst structures, burial of catalytic sites and volatilization of metals. The experimental results demonstrate that the pyrolysis of [Zn{P4Mo6}2] can etch Co-NCNTs-800 to produce a porous structure with an enlarged specific surface area, thus increasing the number of catalytic sites and promoting the transfer of electrons/ions. The high-valence Mo atoms from the POM precursor are inclined to hybridize with O active intermediates produced during ORR/OER, which can improve electron exchange and the ORR/OER performance. Furthermore, the multi-catalytic sites (Zn and Mo2C, etc.) produced from the [Zn{P4Mo6}2] precursor can not only facilitate ORR/OER at the battery cathode, but also inhibit the formation of zinc dendrites by forming a large number of nucleation sites on the battery anode. Accordingly, the ZABs assembled with the POM-derived catalyst exhibit a high open circuit voltage of 1.506 V and a peak power density of 223.54 mW cm−2. Moreover, the assembled all-solid coin cell ZABs also display high capacity and long-term charge–discharge stability. Furthermore, density functional theory calculations demonstrate that the synergy between Zn/Mo2C and Co-NCNTs active sites mainly contributes to the superior ORR/OER catalytic performance.

Solvent-free synthesis of Co/CoNx encapsulated by N-doped, sucrose-derived porous carbon as bifunctional air cathode catalyst for high-energy rechargeable zinc-air batteries

Rechargeable zinc-air batteries have a substantial theoretical energy density while potentially being manufactured at a minimized cost. Hence, developing low-cost bifunctional electrocatalysts is of crucial importance. Herein, the synthesis of an electrocatalyst containing zinc/cobalt species encapsulated in a nitrogen-doped carbon matrix modulated with a large number of carbon nanotubes (ZnCo@CN) was developed through a facile thermal method under solvent-free conditions. Using bio-based sucrose in the presence of inorganic catalysts (Zn/Co) resulted in a Zn/Co carbon foam-like structure. Subsequently, the high-temperature treatment with the addition of 2-methylimidazole resulted in a unique material (ZnCo@CN). The incorporation of highly active species dispersed in hierarchical porous carbon presented an excellent bifunctional electrocatalyst for ORR (half-wave potential of 0.85 V) and OER (overpotential of 327 mV). The assembled zinc-air battery with ZnCo@CN as a bifunctional air cathode exhibited an excellent power density of 206 mW cm-2 and an astonishing energy density of 983 Wh Kg-1.

High Performance Air Breathing Zinc-Air Battery with Pt−Ni and Pt−Co Bifunctional Electrocatalyst on N Activated Mesoporous Carbon

In future perspective, the world demands energy conversion and storage devices with high efficiency, lower cost, reliability and sustainability. Zinc air battery (ZAB) has proven capable as metal anodes for producing such energy, as they are Earth-abundant economical, and environmentally resilient, suitable for efficient domestic and industrial applications. Herein, we developed a catalyst, which serves as an excellent bi-functional cathode catalyst for ZAB. Platinum alloy with the transition metals (nickel and cobalt) supported on the nitrogen doped bio derived high mesoporous carbon using a facile method. This catalyst shows the remarkable performance on both the oxygen reduction reaction and oxygen evolution reaction. Platinum alloy (Pt-Ni and Pt-Co) supported on N-activated bio derived mesoporous carbon (N-MC) shows low over potential and high half wave potential over the commercial catalyst in the oxygen reduction reaction. While performance analysis in in-house designed air breathing ZAB, the outstanding performances are achieved with the specific capacity of 746 mAh g−1 for Pt-Co/N-MC and 726 mAh g−1 for Pt-Ni/N-MC, which surpass the commercial Pt-Ru/C catalyst which shows a specific capacity of 420 mAh g−1. The admirable cycling stability over 110 cycles were observed for Pt-Co/N-MC. Undoubtedly, Pt-Co/N-MC and Pt-Ni/N-MC are promising candidates for bi-functional air cathode catalyst for air breathing zinc air battery.

Boosting the Bifunctional Oxygen Electrode Activity of Nitrogen-decorated Carbon Networks via Ni/NiO Addition for Li-Air and Zn-Air Batteries

Designing efficient and cost-effective oxygen electrode catalysts for metal-air batteries is the most intrinsic requisite for next-generation energy storage devices. In this work, bifunctional air-breathing electrode catalysts made of nitrogen-doped carbon (NC) and nickel/nickel oxide/nitrogen-doped carbon (NNONC) nanocomposites are explored for rechargeable Li-Air and Zn-Air batteries. The integration of Ni/NiO nanoparticles on the NC enhances the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities of the NC. Ni, nickel oxide, and NC acted synergistically to create additional reaction sites, high conductivity, and rapid diffusion pathways, resulting in increased catalytic activity. The CR-2032 coin-type and split cell Li-Air batteries were made with NNONC composite as cathode and Lithium metal as anode. The split cell had a high discharge capacity of 3330 mA h g−1 at a current density of 100 mA g−1. Moreover, the NNONC used as bifunctional cathode catalyst in the rechargeable Zn-Air battery. Where Anode is made of zinc-can from a used zinc carbon battery. The Zn-Air battery has good electrochemical activity, such as good cycle life and low overpotentials of 0.31 and 0.19 V for charging and discharging, respectively. Thus, NNONC can be a promising bifunctional catalyst for both the non–aqueous and aqueous rechargeable metal–air batteries.

Covalent organic frameworks with Ni-Bis(dithiolene) and Co-porphyrin units as bifunctional catalysts for Li-O2 batteries.

The rational design of efficient and stable catalysts for the oxygen reduction reaction and oxygen evolution reaction (ORR/OER) is the key to improving Li-O2 battery performance. Here, we report the construction of ORR/OER bifunctional cathode catalysts in a covalent organic framework (COF) platform by simultaneously incorporating Ni-bis(dithiolene) and Co-porphyrin units. The resulting bimetallic Ni/Co-COF exhibits high surface area, fairly good electrical conductivity, and excellent chemical stability. Li-O2 batteries with the Ni/Co-COF-based cathode show a low discharge/charge potential gap (1.0 V) and stable cycling (200 cycles) at a current density of 500 mA g-1, rivaling that of PtAu nanocrystals. Density functional theory computations and control experiments using nonmetal or single metal-based isostructural COFs reveal the critical role of Ni and Co sites in reducing the discharge/charge overpotentials and regulating the Li2O2 deposition. This work highlights the advantage of bimetallic COFs in the rational design of efficient and stable Li-O2 batteries.

Lignin-based nitrogen/sulfur dual-doped nanosheets decorated with Co1−xS nanoparticles as efficient bifunctional oxygen electrocatalysts

The development of efficient, cost-effective, bifunctional cathode catalyst materials to replace precious metals is highly attractive for the fabrication of Zn–air battery. Here, the three–dimensional N and S co–doped carbon nanosheets loaded with cobalt sulfide nanoparticles (Co1-xS@SNFC) for bifunctional oxygen electrocatalysis were synthesized with Co(NO3)2·6H2O as the Co source, lignin as the carbon source, thiourea as the nitrogen/ sulfur source, and MgO as the template. The synergistic effect of multiple active sites gives the Co1-xS@SNFC fast electrochemical kinetic properties and excellent stability to oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). The half-wave potential and overpotential of Co1-xS@SNFC were 0.84 mV and 306 mV, respectively, which is closed to commercial noble metal catalysts. In addition, Co1-xS@SNFC exhibited four–electron transfer characteristics and ultra–low tafel slope. Compared with commercial Pt/C, the Zn–air battery assembled from Co1-xS@SNFC exhibited a low voltage gap of polarization curve (0.75 V) between charging and discharge and high power density (207 mWcm−2) in alkaline electrolyte. This work developed a green and novel fabrication approach for the synthesis of bifunctional electrocatalyst and provides a new idea for high-value utilization of biomass.

Highly Stable Single‐Atom Modified MXenes as Cathode‐Active Bifunctional Catalysts in Li–CO2 Battery

AbstractThe exploration of cathode catalysts with low overpotentials for the carbon dioxide reduction reaction (CRR) and carbon dioxide evolution reaction (CER) is essential for Li–CO2 batteries. MXenes have been suggested as potential candidates owing to their high electrical conductivity and effective CO2 activation performance. Herein, the stability and bifunctional CRR/CER catalytic activities of bare MXene (M2C), oxygen‐functionalized MXene (M2CO2), and single‐atom (SA) modified M2CO2 are systemically investigated. Among bare MXenes, Mo2C exhibits the best catalytic activity, comparable to that of carbon nanotubes, whereas oxygen‐functionalized MXene has poor activity. Notably, introducing an SA on the surface of oxygen‐functionalized MXene decreases the overpotential by 12.2%–68.1%, which can even outperform graphene catalysts, suggesting their potential as bifunctional cathode catalysts in Li–CO2 batteries. This high activity is appropriate reactivity in origin, as highlighted by the volcano‐type relationship between the Gibbs free energy and the overpotential for key steps. The descriptor ξ, which is related to adsorption behavior, is effective in determining bifunctional catalytic activity, which depends on the ability of SA electrons to fill antibonding orbitals and SA–oxygen/carbon bonding. This study not only identifies promising MXene‐based bifunctional CRR/CER catalysts but also provides a rational design rule for SA modified catalysts.