Catalyst Oxygen Research Articles

FeNiCrCoMn High-Entropy Alloy Nanoparticles Loaded on Carbon Nanotubes as Bifunctional Oxygen Catalysts for Rechargeable Zinc-Air Batteries.

An efficient and stable bifunctional oxygen catalyst is necessary to complete the application of the rechargeable zinc-air battery. Herein, an economical and convenient process was adopted to successfully coat high-entropy alloy Fe12Ni23Cr10Co55-xMnx nanoparticles on carbon nanotubes (CNTs). In 0.1 M KOH solution, with a bifunctional oxygen overpotential (ΔE) of only 0.7 V, the catalyst Fe12Ni23Cr10Co30Mn25/CNT exhibits excellent bifunctional oxygen catalytic performance, exceeding most catalysts reported so far. In addition, the air electrode assembled with this catalyst exhibits high specific capacity (760 mA h g-1) and energy density (865.5 W h kg-1) in a liquid zinc-air battery, with a long-term cycle stability over 256 h. The density functional theory calculation points out that changing the atomic ratio of Co/Mn can change the adsorption energy of the oxygen intermediate (*OOH), which allows the ORR catalytic process to be accelerated in the alkaline environment, thereby increasing the ORR catalytic activity. This article has important implications for the progress of commercially available bifunctional oxygen catalysts and their applications in zinc-air batteries.

Interface and doping engineering of Co-based electrocatalysts for enhanced oxygen reduction and evolution reactions

The fabrication of highly efficient bifunctional catalyst for oxygen evolution/reduction reaction (OER/ORR) is essential for high performance rechargeable Zn-air batteries. Herein, we present a method of simultaneous interface/doping engineering to prepare bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries. The Fe-Co2P/Co heterostructure was covered by N-doped carbon boxes (Fe-Co2P/Co@NC), and the surface electronic structure of Fe-Co2P/Co@NC was tailored through the controlled co-doping of P and Fe. Theoretical calculation revealed a significant charge accumulation at the interface of Fe-Co2P and Co, demonstrating a strong synergy in Fe-Co2P/Co@NC catalyst. The as-prepared Fe-Co2P/Co@NC catalyst exhibited an excellent catalytic performance for ORR/OER as well as rechargeable Zn-air batteries with large power density (783 mA h gZn−1), high open circuit voltage (1.54 V) and long charge/discharge stability (155 h). This work provides a new approach for the construction of interface-rich heterostructure electrocatalysts for oxygen catalysis.

Phase engineering and surface reconstruction of CrxMnFeNi high entropy alloys for electrocatalytic water splitting

The quest for cost-effective and efficient catalysts for oxygen and hydrogen evolution reactions is vital for a carbon-neutral future. High entropy alloys (HEAs), known for their exceptional thermodynamic stability and performance, have recently emerged as promising candidates in this field. Yet, the relationship between the phase and catalytic performance in HEAs remains understudied. Commonly, metallic catalysts undergo surface reconstruction under high oxidizing potentials under the oxygen evolution reaction (OER), making the identification of the truly active species essential for designing efficient catalysts. Nonetheless, characterization of surface reconstruction of nanoscale HEAs is challenging due to low content of each metal, exacerbated by the use of nonmetal support during synthesis. In this study, we unveil the phase-performance relationship in HEAs and identify that the body-centered cubic (BCC) phase CrMnFeNi outperforms its face-center cubic (FCC) phase counterparts in catalyzing both OER and the hydrogen evolution reaction (HER) due to its superior electrical conductivity and optimized electronic structures. Particularly, Cr1.5MnFeNi with the most prominent BCC phase demonstrates superior OER activity (η10 of 255 mV and Tafel slope of 28.7 mV dec−1), surpassing other Cr, Mn, Fe, Ni-based catalysts, and even state-of-the-art RuO2. X-ray photoelectron spectroscopy (XPS) analysis a transition of Mn, Fe, and Ni elements from metallic states to oxidation states, with surface dissolution of Cr after OER durability tests. This research elucidates the phase-dependent electrocatalytic performance and surface reconstruction in HEAs, providing valuable insights for designing and optimizing HEA materials for electrocatalytic applications.

Spatially confined sub-nanometer Pt in RuO2 nanosheet as robust bifunctional oxygen electrocatalyst for stabilizing Li-O2 batteries

Developing a highly active and durable bifunctional oxygen catalyst is the key to boosting lithium-oxygen batteries, but it remains a grand challenge. Herein, we demonstrate a remarkably active and durable bifunctional electrocatalyst (Pt/RuO2/G) with highly exposed active sites for stabilizing Li-O2 batteries by synergistically coupling the advanced oxygen reduction reaction (ORR) catalyst Pt with the oxygen evolution reaction (OER) catalyst RuO2, strongly anchored on graphene. The combined merits, including 2D porous morphology, ultrathin thickness (∼2.5 nm), and a well-dominated (110) plane of ultrasmall RuO2, originating from the efficient spatial confinement, provide the bifunctional Pt/RuO2/G electrocatalyst an extremely narrow OER/ORR voltage gap of only 0.633 V. Moreover, the as-designed Pt/RuO2/G-based Li-O2 batteries deliver a low initial charge-discharge mid-capacity overpotential (0.78 V) and remarkable lifetime (2,200 h) at 200 mA g−1, outperforming most Ru-based catalysts for Li-O2 batteries. This work provides a reliable practical approach for high-performance Li-O2 batteries.

MOF–Derived N–Doped C @ CoO/MoC Heterojunction Composite for Efficient Oxygen Reduction Reaction and Long-Life Zn–Air Battery

The high activity and reliability of bifunctional oxygen catalysts are imperative for rechargeable metal–air batteries. However, the preparation of bifunctional non–noble metal electrocatalysts with multiple active sites remains a great challenge. Herein, an MOF–derived N–doped C–loaded uniformly dispersed CoO/MoC heterojunction catalyst for high–performance dual function was prepared by a simple “codeposition–pyrolysis” method. Experimental investigations revealed that the formation of the heterojunction can tailor the valence of Co and Mo sites, which impressively modulates the electronic properties of the active sites and promotes the electrocatalytic processes. The optimal catalyst reveals a high–wave half potential (E1/2 = 0.841 V) for ORR and a low overpotential (E10 = 348 mV) for OER. The NCCM–600–based Zn–air battery displays a high peak power density of 133.36 mW cm−2 and a prolonged cycling life of more than 650 h. This work provides avenues for the development of functional materials with enhanced properties in a variety of practical energy applications.

Effect of cathode catalyst layer on proton exchange membrane fuel cell performance: Considering the spatially variable distribution

The effect of the ionomer spatial distribution in the cathode catalyst layer (CCL) of the proton exchange membrane fuel cell (PEMFC) on oxygen and proton transport has been extensively studied. However, models generally assume a mean spatial distribution (MSD) of ionomer, and consideration of the actual spatial distribution (ASD) is indeed insufficient. In this study, a multi-dimensional PEMFC model is developed to investigate the effect of ionomer ASD versus MSD on cell performance. In addition, we corrected the Damkohler number (Da) by taking into account the local oxygen transport interfacial resistance and catalyst parameters into δ (an effective ionomer thickness), which allows Da to more accurately reflect the oxygen supply. The results show that the MSD assumption for ionomer tends to underestimate cell performance at the same current density. The proton transport resistance of ASD is 3.17% higher than that of MSD, but the oxygen concentration is 42.8% larger. This is mainly attributed to the larger porosity and lower saturation near the CCL/CMPL interface in the ASD model, which facilitates oxygen transport. The Da sufficiently supports the results, and the Da at the CCL/MPL interface of the ASD model (0.34) is smaller than in the MSD model (0.82), indicating relative oxygen enrichment. This study provides guidance for future PEMFC models.

Edge atomic Fe sites decorated porous graphitic carbon as an efficient bifunctional oxygen catalyst for Zinc-air batteries

The development of advanced bifunctional oxygen electrocatalysts for oxygen reduction and evolution reactions (ORR and OER) is critical to the practical application of zinc-air batteries (ZABs). Herein, a silica-assisted method is reported to integrate numerous accessible edge Fe-Nx sites into porous graphitic carbon (named Fe-N-G) for achieving highly active and robust oxygen electrocatalysis. Silica facilitates the formation of edge Fe-Nx sites and dense graphitic domains in carbon by inhibiting iron aggregation. The purification process creates a well-developed mass transfer channel for Fe-N-G. Consequently, Fe-N-G delivers a half-wave potential of 0.859 V in ORR and an overpotential of 344 mV at 10 mA cm−2 in OER. During long-term operation, the graphitic layers protect edge Fe-Nx sites from demetallation in ORR and synergize with FeOOH species endowing Fe-N-G with enhanced OER activity. Density functional theory calculations reveal that the edge Fe-Nx site is superior to the in-plane Fe-Nx site in terms of OH* dissociation in ORR and OOH* formation in OER. The constructed ZAB based on Fe-N-G cathode shows a higher peak power density of 133 mW cm−2 and more stable cycling performance than Pt/C + RuO2 counterparts. This work provides a novel strategy to obtain high-efficiency bifunctional oxygen electrocatalysts through space mediation.

Synergetic C–H bond activation and C–O formation on CuOx facilities facile conversion of methane to methanol

Direct methane to methanol conversion is desirable but difficult to implement due to the inertness of methane and unattainable matching oxidant. The capability of Cu oxides releasing lattice oxygen makes it a potential oxidant to facilitate the conversion. Herein, the mechanism of methane to methanol on the surfaces of CuOx has been studied using density functional theory calculations. Heterolytic cleavage of the C–H bond is preferred at the Cu–O site whereas methanol formation from dissociated CH3 and H on surface O can take place over either Cu–O or O–O site. On CuO(1¯1 1), methane activation at the Cu–O site and methanol formation over the O–O site synergistically enable the selective oxidation of methane to methanol. In contrast, the formation of methanol on the O-deficient surfaces is a result of direct coupling of CH3 on Cu and OH formed from of H adsorbed on the surface O site. Microkinetics analysis confirms the synergistic effect of Cu–O and O–O on CuO(1¯1 1) for methanol formation in a temperature range of 473–648 K. These findings demonstrate the feasibility of selective oxidation of methane to methanol with the surface lattice oxygen of CuOx and help to design the CuOx-based oxygen carriers and/or catalysts.

Bimetallic ZIFs-derived electrospun carbon nanofiber membrane as bifunctional oxygen electrocatalyst for rechargeable zinc-air battery

The recharged zinc-air battery (ZAB) has drawn significant attention owing to increasing requirement for energy conversion and storage devices. Fabricating the efficient bifunctional oxygen catalyst using a convenient strategy is vitally important for the rechargeable ZAB. In this study, the bimetallic ZIFs-containing electrospun (ES) carbon nanofibers membrane with hierarchically porous structure was prepared by coaxial electrospinning and carbonization process, which was expected to be a bifunctional electrocatalyst for ZABs. Owing to the formed dual single-atomic sites of Co–N4 and Zn–N4, the obtained ES-Co/Zn-CNZIF exhibited the preferable performance toward oxygen reduction reaction (ORR) with E1/2 of 0.857 V and JL of 5.52 mA cm−2, which were more than Pt/C. Meanwhile, it exhibited a marked oxygen evolution reaction (OER) property with overpotential of 462 mV due to the agglomerated metallic Co nanoparticles. Furthermore, the ZAB based on the ES-Co/Zn-CNZIF carbon nanofibers membranes delivered peak power density of 215 mW cm−2, specific capacity of 802.6 mA h g−1, and exceptional cycling stability, far larger than Pt/C+RuO2-based ZABs. A solid-state ZAB based on ES-Co/Zn-CNZIF showed better flexibility and stability with different bending angles.

Facile preparation and properties of high nitrogen-containing Fe/Co/N co-doped three-dimensional graphene bifunctional oxygen catalysts for zinc air battery

Fe/Co/N co-doped multi-channel interpenetrating three-dimensional graphene catalyst (FeCo–N-3D-HG) with good oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic performances is prepared by a facile method, using poly (2,5-benzimidazole) (ABPBI), iron salt, cobalt salt and nanometer CaCO3 (template). ABPBI forms a complex with iron and cobalt ions and the complex is coated on the surface of CaCO3. The pyrolysis process is carried out in an Ar gas protection, the template is removed by acid to obtain FeCo–N-3D-HG. The results show that FeCo–N-3D-HG is three-dimensional multi-layered graphene structure with multi-channels. The catalytic performance of ORR (E1/2 = 0.860 V vs RHE) is better than 20 wt% Pt/C in O2 saturated 0.1 M KOH electrolyte. The catalyst also shows similar OER performance with the RuO2 in 1 M KOH solution. The prepared zinc-air battery exhibits outstanding peak power density (261.7 mW cm−2), preeminent specific capacity (760.1 mAh g−1), and good cycle durability (150 h).

Optimization of metal-supported solid oxide electrolysis cells with infiltrated catalysts

Metal-supported solid oxide electrolysis cells (MS-SOECs) are being developed for steam-to-hydrogen electrolysis, especially for utilization of dynamic or intermittent electrical power from renewable sources. Various aspects of the electrocatalyst processing and composition, and metal support structure were explored. Catalyst materials, infiltration temperature and infiltration cycles were optimized for high performance and durability. Numerous catalyst materials were screened for both oxygen and steam electrodes. The oxygen catalyst had moderate impact on both initial cell performance and durability. Reducing Ni content in the steam electrode had little effect on durability, but reduced initial performance. Ex-situ XRD analysis and cell assessment of catalyst infiltration temperature revealed that the optimal range is 750–850 °C. The best cell performance and durability was achieved with LSCF-SDC oxygen electrocatalyst and SDC-Ni (60:40 vol%) steam electrocatalyst infiltrated 11 times at 800 °C and operated at 700 °C. At low steam content, a significant mass transport limitation on the steam side results in limiting current behavior. Thinner and more porous metal supports were implemented, and found to improve steam mass transport at low steam content, relevant for SOECs operating under high H2 recycle rate or high steam utilization.

Quenching-induced surface reconstruction of perovskite oxide for rapid and durable oxygen catalysise

Rapid degradation of catalytic activity for oxygen reduction reaction has become key factor in restricting practical applications of perovskite oxide in solid oxide fuel cells. Herein, quenching is disclosed to be an effective method to bring rapid and durable oxygen catalysis of perovskite-structured Pr0.5Ba0.25Ca0.25CoO3-δ. The quenching processing, cooling rate is around 8000 times higher than that of traditional annealing process, could turn the output power density of single cells from the decay process with a rate of 17.1% into an upsurge process with a rate of 18.4%, resulting in a stable power density of 0.72 W cm−2. This relates to a large number of point defects, dislocations, disorder and nanocrystalline domains are formed in perovskite oxides by quenching. These chemical defects can drive cationic diffusion to the surface indiscriminately, forming electroactive perovskite-structured nanoparticles. This work provides a new technology and concept to optimize the performance of perovskite-structured oxygen catalysts.

String of ZIF-derived hollow beaded nanocage embedded into carbon nanofiber with intensified exposed Co-Nx sites for efficient oxygen catalysis in various fuel cell devices

The rational control of Co-Nx active sites dispersion in nanomaterials is significant to construct efficient oxygen reduction reaction (ORR) electrocatalysts in fuel cells. Herein, a novel strategy for the scalable synthesis of carbon nanofiber supported hollow beaded nanocage with accessible Co-Nx sites in cavity wall (PAN-Co-ZIF-8-C-A and PAN-Co/ZIF-8-C-A) originated from zeolitic imidazolate frameworks (ZIFs) and polyacrylonitrile (PAN) is reported. Remarkably, the formed samples modified with Co-Nx sites exhibit superior ORR activity, which makes it promising ORR catalysts for microbial fuel cell (MFC) and direct methanol fuel cell (DMFC). Accordingly, the maximum power densities of MFC decorated with PAN-Co-ZIF-8-C-A and PAN-Co/ZIF-8-C-A achieve 869.6 and 888.3 mW cm−2, which are 1.17 and 1.19 times higher than that of Pt/C. In addition, the PAN-Co/ZIF-8-C-A modified DMFC exhibits comparable power density of 23.27 mW cm−2 close to Pt/C electrode (25.63 mW cm−2). Such commendable catalytic performances can be primarily attributed to the synergistic effect of hierarchical porosity for fast mass transport, high conductivity for electron migration, and well-tuned Co-Nx sites for oxygen reduction. This facile-effective optimization strategy may open a new avenue for exposing the catalytic centers of one-dimensional (1D) nanofiber and ZIFs-derived oxygen catalyst in fuel cells.

Understanding the Role of (W, Mo, Sb) Dopants in the Catalyst Evolution and Activity Enhancement of Co3 O4 during Water Electrolysis via In Situ Spectroelectrochemical Techniques.

Unlocking the potential of the hydrogen economy is dependent on achieving green hydrogen (H2 ) production at competitive costs. Engineering highly active and durable catalysts for both oxygen and hydrogen evolution reactions (OER and HER) from earth-abundant elements is key to decreasing costs of electrolysis, a carbon-free route for H2 production. Here, a scalable strategy to prepare doped cobalt oxide (Co3 O4 ) electrocatalysts with ultralow loading, disclosing the role of tungsten (W), molybdenum (Mo), and antimony (Sb) dopants in enhancing OER/HER activity in alkaline conditions, is reported. In situ Raman and X-ray absorption spectroscopies, and electrochemical measurements demonstrate that the dopants do not alter the reaction mechanisms but increase the bulk conductivity and density of redox active sites. As a result, the W-doped Co3 O4 electrode requires ≈390 and ≈560mV overpotentials to reach ±10 and ±100mA cm-2 for OER and HER, respectively, over long-term electrolysis. Furthermore, optimal Mo-doping leads to the highest OER and HER activities of 8524 and 634 A g-1 at overpotentials of 0.67 and 0.45V, respectively. These novel insights provide directions for the effective engineering of Co3 O4 as a low-cost material for green hydrogen electrocatalysis at large scales.

Suppressing the Surface Amorphization of Ba0.5Sr0.5Co0.8Fe0.2O3-δ Perovskite toward Oxygen Catalytic Reactions by Introducing the Compressive Stress.

Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) perovskite has been recognized as a promising oxygen evolution reaction (OER) catalyst due to its superior intrinsic catalytic activity. However, BSCF suffers from serious degradation during the OER process due to its surface amorphization caused by the segregation of A-site ions (Ba2+ and Sr2+). Herein, we construct a novel BSCF composite catalyst (BSCF-GDC-NR) by anchoring the gadolinium-doped ceria oxide (GDC) nanoparticles on the surface of a BSCF nanorod by a concentration-difference electrospinning method. Our BSCF-GDC-NR has greatly improved bifunctional oxygen catalytic activity and stability toward both oxygen reduction reaction (ORR) and OER compared with the pristine BSCF. The improvement of the stability can be related to that anchoring GDC on BSCF effectively suppresses the segregation and dissolution of A-site elements in BSCF during the preparation and catalytic processes. The suppression effects are ascribed to the introduction of compressive stress between BSCF and GDC, which greatly inhibits the diffusions of Ba and Sr ions. This work can give a guidance for developing the perovskite oxygen catalysts with high activity and stability.

Dual Active Sites Engineering on Sea Urchin‐Like CoNiS Hollow Nanosphere for Stabilizing Oxygen Electrocatalysis via a Template‐Free Vulcanization Strategy

AbstractManipulating electronic structure and defects is crucial to achieve on‐demand functionalities of bimetallic sulfide catalysts for oxygen reduction/evolution reactions (ORR/OER). Here, via a vulcanization strategy, defects‐abundant NiCo2S4 needles obtained from sea urchin‐like NiCo2O4 are anchored on surface of hollow carbon‐sphere (NiCo2S4/HCS). NiCo2S4 nanoneedles (≈7.5 nm) are radially grown on shell of HCS with a cavity (254.5 m2 g−1), and their surface becomes rougher after vulcanization due to anion exchange reaction. As‐marked NiCo2S4/HCS‐3 exhibits better ORR activity (half‐wave potential of 0.89 V) and methanol tolerance than Pt/C (0.86 V). NiCo2S4/HCS‐3 shows a lower OER overpotential (310 mV) than RuO2 and retains 90.9% of initial activity after 9 h. Notably, zinc–air battery with NiCo2S4/HCS‐3 reveals highly‐stable charging/discharging voltages of 2.11/1.16 V with a negligible fading for 200 h. NiCo2S4 grown on outer/inner surfaces of HCS expands spatial distribution of active sites to enhance reactants‐electrode contact and charge transfer. Theoretical calculation shows that Co‐site with an electronic state near Fermi energy level is chiefly‐responsible for ORR, while Ni‐site mainly affords high OER activity. Bader charge analyses reveal that S doping increases the charge density and redox active sites in NiCo2S4. It sheds light on the understanding of electrocatalytic mechanisms on bimetallic sulfides for electronic device.

Tracking the Seconds of a Clock Reaction: A Multiparametric Experimental Study on the Catalytic Reduction of Methylene Blue

The catalytic reduction and subsequent reoxidation of methylene blue (MB) is a well-known reaction, commonly referred to as a “clock reaction”. Specifically, the reduction process is accompanied by a color change from intense blue to clear and can be readily monitored by UV–vis spectroscopy via the decrease in absorbance at λmax = 664 nm, providing facile access to valuable reaction kinetics. Unsurprisingly, the reduction of methylene blue has become a widely used probe for heterogeneous catalyst reactivity. Yet, despite its broad utility, the mechanism of reduction is not well-understood. Herein, we report an experimental study on the mechanism of MB reduction using Pt/C nanoparticles. Through a multiparametric study incorporating in situ probing of reaction kinetics, pH, dissolved oxygen, and variable catalyst and reductant loading, the multiple factors impacting the reaction are disentangled. We demonstrate that the reaction steps that limit the reduction of MB are the H2 evolution and reoxidation sequences. We limit these competitive reactions by optimizing reductant concentration and catalyst loading, N2 purging, and restriction of O2 redissolution. This achieves a highly competitive activity parameter of 25,740 min–1 gPt–1 L.

In situ growth of N-doped carbon nanotubes in Fe-Nx/Fe2O3/Fe3O4-encapsulated carbon sheets for efficient bifunctional oxygen catalysis

Development of efficient bifunctional oxygen catalysts is of interest for zinc-air batteries (ZABs). However, achieving both highly active and durable oxygen reduction and evolution reactions (ORR/OER) in one catalyst remains challenging. Herein, a composite catalyst (m-Fe/N-C@CNT) integrating N-doped carbon nanotubes (NCNTs) and Fe-Nx/Fe2O3/Fe3O4-encapsulated carbon nanosheets is obtained by in situ growth and interface induction strategy. SiO2 is modified with amine groups to anchor Fe3+ and inhibit Fe3+ reduction, and the resulting Fe2O3/Fe3O4 nanoparticles convert g-C3N4 to NCNTs. m-Fe/N-C@CNT shows superior activity and stability to commercial Pt/C and RuO2 catalysts in ORR and OER, respectively. The high activity of m-Fe/N-C@CNT is revealed to mainly derive from Fe-Nx moieties, and the contributions of N-C and Fe2O3/Fe3O4 species are reflected in ORR and OER, respectively. Moreover, the constructed ZABs exhibit a peak power density of 160 mW cm−2 and recyclability. This work provides a new idea for the preparation of bifunctional oxygen catalysts.

Cobalt Nanoparticles Encapsulated with N-Doped Bamboo-Like Carbon Nanofibers as Bifunctional Catalysts for Oxygen Reduction/Evolution Reactions in a Wide pH Range

Nonprecious bifunctional oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) catalysts in wide pH electrolytes are crucial for the versatile use of electrochemical energy storage and conversion devices. Non-noble metal/nitrogen-doped carbon (M–N/C) has been reported as a promising candidate for efficient and cost-effective bifunctional catalysts. Nevertheless, the stability and catalytic activity of M–N/C bifunctional catalysts in a wide pH range are still limited, especially in neutral and acidic electrolytes. Here, we synthesized directly grown N-doped bamboo-like carbon nanofiber-encapsulated cobalt nanoparticles on carbon flakes (Co–N/C fiber) via pyrolysis of 2D cobalt–zeolitic imidazolate framework and tubular g-C3N4. The in situ growth of N-doped carbon nanofiber incorporated with Co nanoparticles exposes large active sites and enhances charge transfer. Moreover, abundant mesopores with high loading of pyridinic-N, graphitic-N, Co@N/C, and Co–Nx facilitate high catalytic activity in a wide pH condition. Co–N/C fiber shows superior ORR performance in alkaline, neutral, and acidic electrolytes with high onset potentials of 1.003, 0.820, and 0.800 V vs RHE, respectively. A comparable OER performance of Co–N/C fiber to the Ir/C benchmark in alkaline and neutral conditions can be obtained with 397 and 570 mV overpotentials at 10 mA cm–2. Utilizing Co–N/C fiber in alkaline and neutral Zn–air batteries exhibits power densities of 155 and 67 mW cm–2, with excellent stability for over 180 h. This study offers a strategy for developing a bifunctional M–N/C catalyst that is applicable across a wide pH range via hybrid nanostructuring.

In-situ desalination-coupled electrolysis with concurrent one-step-synthesis of value-added chemicals

An efficient multi-functional electrolyzer with a Ni- and Fe-layered double hydroxide (NiFe-LDH) anode and a binary NiMo cathode is designed for overall water splitting coupled with the desalination of saline water and production of value-added chemicals. The NiFe-LDH and NiMo pairs separated by a bipolar membrane (BPM) show overpotentials as low as those of noble metal catalysts for oxygen and hydrogen evolution reactions in 1 M KOH and 1 M H2SO4 solutions, respectively. Arraying anion and cation-exchange membranes (AEMs and CEMs, respectively) with BPMs (NiFe-LDH/BPM/[AEM/CEM]n/BPM/NiMo; n = 1 or 5) further enables the desalination of brackish water and seawater at specific energy consumption of 1.8 kWh m−3, with concurrent production of HCl and NaOH. The Faradaic efficiencies of the device for O2 and H2 production are >95 % at J = 100 mA cm−2 over 20 h, while the initial pH values of the anolyte and catholyte remain unchanged. Detailed surface characterization of the electrocatalysts is performed, and various electrolyzer configurations are compared in terms of desalination efficiency.