Hierarchically Porous Co/Cox My (M = P, N) as an Efficient Mott-Schottky Electrocatalyst for Oxygen Evolution in Rechargeable Zn-Air Batteries

Amorphous P-CoOX Promotes the Formation of Hypervalent Ni Species in NiFe LDHs by Amorphous/Crystalline Interfaces for Excellent Catalytic Performance of Oxygen Evolution Reaction

Water electrolysis has become an attractive hydrogen production method. Oxygen evolution reaction (OER) is a bottleneck of water splitting as its four-electron transfer procedure presents sluggish reaction kinetics. Designing composite catalysts with high performance for efficient OER still remains a huge challenge. Here, the P-doped cobalt oxide/NiFe layered double hydroxides (P-CoOX/NiFe LDHs) composite catalysts with amorphous/crystalline interfaces are successfully prepared for OER by hydrothermal-electrodeposition combined method. The results of electrochemical characterizations, operando Raman spectra, and DFT theoretical calculations have demonstrated the electrons in the P-CoOX/NiFe LDHs heterointerfaces are easily transferred from Ni2+ to Co3+ because that the amorphous configuration of P-CoOX can well induce Ni-O-Co orbital coupling. The electron transfer of Ni2+ to the surrounding Fe3+ and Co3+ will lead to the unoccupied eg orbitals of Ni3+ that can promote water dissociation and accelerate *OOH migration to improve OER catalytic performance. The optimized P-CoOX/NiFe LDHs exhibit superior catalytic performance for OER with a very low overpotential of 265 mV at 300 mA cm-2 and excellent long-term stability of 500 h with almost no attenuation at 100 mA cm-2. This work will provide a new method to design high-performance NiFe LDHs-based catalysts for OER.

In-situ gas foaming synthesis of N, S-rich co-doped hierarchically ordered porous carbon as an efficient oxygen reduction reaction catalyst

The design and manufacture of cost-effective and efficient oxygen reduction reaction (ORR) catalysts is critical to the widespread application of multiple energy conversion devices. Herein, a combination of in-situ gas foaming and the hard template method is proposed to construct the N, S-rich co-doped hierarchically ordered porous carbon (NSHOPC) as an effective metal-free electrocatalyst for ORR via carbonizing a mixture of polyallyl thiourea (PATU) and thiourea in silica colloidal crystal template (SiO₂-CCT) voids. Benefiting from the hierarchically ordered porous (HOP) architectures and the mass doping of N and S, NSHOPC displays excellent ORR activities (the half-wave potential of 0.889 V in 0.1 M KOH and 0.786 V in 0.5 M H₂SO₄) and long-term stability, which are all better than those of Pt/C. As the air cathode in a Zn-air battery (ZAB), NSHOPC exhibits a high peak power density of 174.6 mW·cm^-2 and long-term discharge stability. The remarkable performance of the as-synthesized NSHOPC signifies broad prospects for actual applications in energy conversion devices.

Nano bowl-like cobalt-cobalt molybdenum carbide coated by N,P co-doped carbon as an advanced bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries

Nano bowl-like Co-Co₆Mo₆C₂ coated by N,P co-doped carbon (Co-Co₆Mo₆C₂@NPC) is reported as an electrocatalyst for Zn-air batteries. Co-Co₆Mo₆C₂@NPC only needs an overpotential of 210 mV at 10 mA cm^-2 for the OER, and the half-wave potential for the ORR is 0.81 V. In addition, the Co-Co₆Mo₆C₂@NPC based battery shows a large open-circuit voltage of 1.335 V and a maximum power density of 160.5 mW cm^-2, as well as good stability. The improved catalytic performance can be ascribed to the co-existence of Co₆Mo₆C₂ and Co species to improve the intrinsic catalytic activity, and the bowl-like nanostructure to facilitate the mass transfer.

Facile construction of robust Ru-Co3O4 Mott-Schottky catalyst enabling efficient dehydrogenation of ammonia borane for hydrogen generation

Developing efficient catalysts for the dehydrogenation of ammonia borane (AB) is important for the safe storage and controlled release of hydrogen, but it is a challenging task. In this study, we designed a robust Ru-Co₃O₄ catalyst using the Mott-Schottky effect to induce favorable charge rearrangement. The self-created electron-rich Co₃O₄ and electron-deficient Ru sites at heterointerfaces are indispensable for the activation of the B-H bond in NH₃BH₃ and the OH bond in H₂O, respectively. The synergistic electronic interaction between the electron-rich Co₃O₄ and electron-deficient Ru sites at the heterointerfaces resulted in an optimal Ru-Co₃O₄ heterostructure that exhibited outstanding catalytic activity for the hydrolysis of AB in the presence of NaOH. The heterostructure had an extremely high hydrogen generation rate (HGR) of 12238 mL min^-1 g_cat^-1 and an expected high turnover frequency (TOF) of 755 mol_H2 mol_Ru^-1 min^-1 at 298 K. The activation energy needed for the hydrolysis was low (36.65 kJ mol^-1). This study opens up a new avenue for the rational design of high-performance catalysts for AB dehydrogenation based on the Mott-Schottky effect.

Substrate Strain Engineering of Single-Atomic Sn-N4 Sites Embedded in Various Carbon Matrixes for Bifunctional Oxygen Electrocatalysis

It is still a great challenge to design and synthesize high-efficiency and low-cost single-atom catalysts (SACs) as promising bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Herein, theoretical insights into Sn-N₄ embedded carbon nanotubes, graphene quantum dots, and graphene nanosheets (denoted as Sn-N₄-CNTs, Sn-N₄-GQDs, and Sn-N₄-Gra, respectively) for the ORR/OER are systematically provided. These results show that the protruding Sn atom creates a Sn-N₄ pyramid and induces varied strain transfer between Sn-N₄ and different carbon substrates prior to adsorption of O intermediates, resulting in the opposite response of the adsorption strengths of O intermediates to the substrate curvature of Sn-N₄-CNTs and Sn-N₄-GQDs. The torsional strain induced by OH* and OOH* on the Sn atom of Sn-N₄-CNTs breaks the scaling relations between the adsorption strengths of O intermediates. Consequently, Sn-N₄-CNTs with suitable curvature achieve outstanding ORR performance with very low overpotentials (0.28 V). Furthermore, the increase of curvature boosts the OER activity of Sn-N₄-CNTs. For Sn-N₄-GQDs, high curvature contributes to promoted OER activity but reduced ORR activity. The electronic interactions reveal the electron transfer from the s/p-bands of Sn to the half-filled β states of the frontier orbitals of O intermediates.

Facilitating interface charge transfer via constructing NiO/NiCo2O4 heterostructure for oxygen evolution reaction under alkaline conditions

Designing high-activity electrocatalysts to enhance the slow multielectron-transfer process of the oxygen evolution reaction (OER) is of great importance for hydrogen generation. Here, we employ hydrothermal and subsequent heat-treatment strategies to acquire nanoarrays-structured NiO/NiCo₂O₄ heterojunction anchored Ni foam (NiO/NiCo₂O₄/NF) as efficient materials for catalyzing the OER in an alkaline electrolyte. Density functional theory (DFT) results demonstrate that NiO/NiCo₂O₄/NF exhibits a smaller overpotential than those of single NiO/NF and NiCo₂O₄/NF owing to interface-triggered numerous interface charge transfer. Moreover, the superior metallic characteristics of NiO/NiCo₂O₄/NF further enhance its electrochemical activity toward OER. Specifically, NiO/NiCo₂O₄/NF delivered a current density of 50 mA cm^-2 at an overpotential of 336 mV with a Tafel slope of 93.2 mV dec^-1 for the OER, which are comparable with those of commercial RuO₂ (310 mV and 68.8 mV dec^-1). Further, an overall water splitting system is preliminarily constructed via using a Pt net as cathode and NiO/NiCo₂O₄/NF as anode. The water electrolysis cell performs an operating voltage of 1.670 V at 20 mA cm^-2, which outperform the Pt net||IrO₂ couple assembled two-electrode electrolyzer (1.725 V at 20 mA cm^-2). This study proposes an efficient route to acquire multicomponent catalysts with rich interfaces for water electrolysis.

Oxygen Evolution/Reduction Reaction Catalysts: From In Situ Monitoring and Reaction Mechanisms to Rational Design

The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are core steps of various energy conversion and storage systems. However, their sluggish reaction kinetics, i.e., the demanding multielectron transfer processes, still render OER/ORR catalysts less efficient for practical applications. Moreover, the complexity of the catalyst-electrolyte interface makes a comprehensive understanding of the intrinsic OER/ORR mechanisms challenging. Fortunately, recent advances of in situ/operando characterization techniques have facilitated the kinetic monitoring of catalysts under reaction conditions. Here we provide selected highlights of recent in situ/operando mechanistic studies of OER/ORR catalysts with the main emphasis placed on heterogeneous systems (primarily discussing first-row transition metals which operate under basic conditions), followed by a brief outlook on molecular catalysts. Key sections in this review are focused on determination of the true active species, identification of the active sites, and monitoring of the reactive intermediates. For in-depth insights into the above factors, a short overview of the metrics for accurate characterizations of OER/ORR catalysts is provided. A combination of the obtained time-resolved reaction information and reliable activity data will then guide the rational design of new catalysts. Strategies such as optimizing the restructuring process as well as overcoming the adsorption-energy scaling relations will be discussed. Finally, pending current challenges and prospects toward the understanding and development of efficient heterogeneous catalysts and selected homogeneous catalysts are presented.

Facile synthesis of Co-Ni layered double hydroxides nanosheets wrapped on a prism-like metal-organic framework for efficient oxygen evolution reaction

The construction of low-cost oxygen evolution reaction (OER) electrocatalysts with high activity and good durability is a considerable challenge for facilitating the efficient utilization of green energy. Herein, the prism-like materials of institute lavoisier frameworks-88 (MIL-88) was first synthesized by a hydrothermal method. Then, Co-Ni layered double hydroxides (CoNi-LDHs) nanosheets were directly wrapped on the MIL-88 surface by electrodeposition to form core-shell MIL-88@CoNi-LDHs composites. Due to the distinct structure and synergistic effect between the MIL-88 core and CoNi-LDHs shell, it was found that MIL-88@CoNi-LDHs had outstanding OER activity with a small Tafel slope (45.55 mV dec^-1), low overpotential (314 mV) at 10 mA cm^-2, and superior durability. This study provides a prospective pathway to exploit highly efficient low-cost electrocatalysts for OER.

Interface engineering of CeO2 nanoparticle/Bi2WO6 nanosheet nanohybrids with oxygen vacancies for oxygen evolution reactions under alkaline conditions

Because of the interactive combination synergy effect, hetero interface engineering is used way for advancing electrocatalytic activity and durability. In this study, we demonstrate that a CeO₂/Bi₂WO₆ heterostructure is synthesized by a hydrothermal method. Electrochemical measurement results indicate that CeO₂/Bi₂WO₆ displays not only more OER catalytic active sites with an overpotential of 390 mV and a Tafel slope of 117 mV dec^-1 but also durability for 10 h (97.57%). Such outstanding characteristics are primarily attributed to (1) the considerable activities by CeO₂ nanoparticles uniformly distributed on Bi₂WO₆ nanosheets and (2) the plentiful Bi-O-Ce and W-O-Ce species playing the role of strong couples between CeO₂ nanoparticles and Bi₂WO₆ nanosheets and oxygen vacancy existence in CeO₂ nanoparticles, which can improve the electrochemical active surface area (ECSA) and activity, and enhance the conductivity for OERs. This CeO₂/Bi₂WO₆ consists of the heterojunction engineering that can open a modern method of thinking for high effective OER electrocatalysts.

FeCo/N-co-doped 3D carbon nanofibers as efficient bifunctional oxygen electrocatalyst for Zn-air batteries

Flexible zinc-air batteries (ZABs) are expected to become a promising candidate in energy storage equipment for wearable electronic devices. However, the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have impeded the development of ZABs. Herein, an FeCo- and N-codoped bifunctional electrocatalyst (FeCoNCF) is fabricated by simple one-pot and pyrolysis strategies. Concretely, the bacterial cellulose (BC) and Prussian blue analogue (PBA) derived transition metal and nitrogen doped carbon (M-N-C) composites provide ORR and OER active sites. FeCoNCF exhibits outstanding ORR and OER activities. It displays a favorable high half-wave potential (0.81 V) and a low overpotential at 10 mA cm^-2 (341 mV), which are on a par with commercial Pt/C and RuO₂, and shows outstanding stability. The sandwich-type flexible zinc-air battery containing FeCoNCF shows a favorable power density (49.29 mW cm^-2) and superior cycling stability.

Facile Electron Transfer in Atomically Coupled Heterointerface for Accelerated Oxygen Evolution

An efficient and cost-effective approach for the development of advanced catalysts has been regarded as a sustainable way for green energy utilization. The general guideline to design active and efficient catalysts for oxygen evolution reaction (OER) is to achieve high intrinsic activity and the exposure of more density of the interfacial active sites. The heterointerface is one of the most attractive ways that plays a key role in electrochemical water oxidation. Herein, atomically cluster-based heterointerface catalysts with strong metal support interaction (SMSI) between WMn₂ O₄ and TiO₂ are designed. In this case, the WMn₂ O₄ nanoflakes are uniformly decorated by TiO₂ particles to create electronic effect on WMn₂ O₄ nanoflakes as confirmed by X-ray absorption near edge fine structure. As a result, the engineered heterointerface requires an OER onset overpotential as low as 200 mV versus reversible hydrogen electrode, which is stable for up to 30 h of test. The outstanding performance and long-term durability are due to SMSI, the exposure of interfacial active sites, and accelerated reaction kinetics. To confirm the synergistic interaction between WMn₂ O₄ and TiO₂ , and the modification of the electronic structure, high-resolution transmission electron microscopy (HR-TEM), X-ray photoemission spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) are used.

Superstructures of Zeolitic Imidazolate Frameworks to Single- and Multiatom Sites for Electrochemical Energy Conversion

The exploration of electrocatalysts with high catalytic activity and long-term stability for electrochemical energy conversion is significant yet remains challenging. Zeolitic imidazolate framework (ZIF)-derived superstructures are a source of atomic-site-containing electrocatalysts. These atomic sites anchor the guest encapsulation and self-assembly of aspheric polyhedral particles produced using microreactor fabrication. This review provides an overview of ZIF-derived superstructures by highlighting some of the key structural types, such as open carbon cages, 1D superstructures, hollow structures, and the interconversion of superstructures. The fundamentals and representative structures are outlined to demonstrate the role of superstructures in the construction of materials with atomic sites, such as single- and dual-atom materials. Then, the roles of ZIF-derived single-atom sites for the electroreduction of CO₂ and electrochemical synthesis of H₂ O₂ are discussed, and their electrochemical performance for energy conversion is outlined. Finally, the perspective on advancing single- and dual-atom electrode-based electrochemical processes with enhanced redox activity and a low-impedance charge-transfer pathway for cathodes is provided. The challenges associated with ZIF-derived superstructures for electrochemical energy conversion are discussed.

Single-thermal synthesis of bimetallic Co/Zn@NC under solvent-free conditions as an efficient dual-functional oxygen electrocatalyst in Zn-air batteries

A straightforward in situ thermal (IST) method is developed to synthesize bimetallic Co/Zn embedded in nitrogen-doped three-dimensional carbon (CoZn@NC_IST). The facile IST process is a single-step thermal treatment of a mixture of metals (Co/Zn) and 2-methylimidazole precursors under solvent-free conditions. This straightforward method is advantageous over the traditional synthesis derived from CoZn-ZIF (CoZn@NC_Solv). During the IST method, the bimetallic Co/Zn bridged with 2-methylimidazole forming zeolitic-imidazole frameworks (ZIFs) under low-temperature (<200 °C) conditions before being de-coordinated and sacrificed their structure into a carbon material at high temperature (>500 °C). Loading zinc into the mixture of precursors contributed to the metal distribution and increased the surface area compared with the sample without zinc (Co@NC_IST). CoZn@NC_IST exhibits a bifunctional electrocatalytic ability for the ORR (0.855 V@E_1/2) and OER (overpotential of 325 mV@10 mA cm^-2). Applying CoZn@NC_IST in a zinc-air battery confirmed its excellent and effective dual-function electrocatalytic performance. Herein, using the advanced single-step method of IST in the absence of any solvent, we provide a powerful and green synthesis of an electrocatalyst that is a potential candidate for industrial applications.

Processable Conjugated Microporous Polymer Gels and Monoliths: Fundamentals and Versatile Applications

Conjugated microporous polymers (CMPs) as a new type of conjugated polymers have attracted extensive attention in academia and industry because of the combination of microporous structure and π-electron conjugated structure. The construction and application of gels and monoliths based on CMPs constitute a fertile area of research, promising to provide solutions to complex environmental and energy issues. This review summarizes and objectively analyzes the latest advances in the construction and application of processable CMP gels and monoliths, linking the basic and enhanced properties to widespread applications. In this review, we open with a summary of the construction methods used to build CMP gels and monoliths and assess the feasibility of different preparation techniques and the advantages of the products. The CMP gels and monoliths with enhanced properties involving various special applications are then deliberated by highlighting relevant scientific literature and discussions. Finally, we present the issues and future of openness in the field, as well as come up with the major challenges hindering further development, to guide researchers in this field.

Anchoring Bimetal Single Atoms and Alloys on N-Doping-Carbon Nanofiber Networks for an Efficient Oxygen Reduction Reaction and Zinc-Air Batteries

Electrocatalysts for the oxygen reduction reaction (ORR) play a central role in fuel cells and zinc-air batteries. Bimetal single atoms and nanoparticle hybrids are emerging ORR electrocatalysts, superior to the most exploited unary metal single-atom catalysts (SACs). Here, we report bimetal SAC-based nanofiber networks of Co₃Fe₇@Co/Fe-SAC for efficient ORR electrocatalysis and zinc-air batteries. A facile and easy-to-scale-up process is developed, and the versatility is validated in three hybrids. Strong electronic interaction is revealed between bimetal single atoms and alloy nanoparticles, leading to improved catalytic performances for ORR. Specifically, the Co₃Fe₇@Co/Fe-SAC hybrids exhibit a half-wave potential of 0.841 V in a basic electrolyte, comparable to the Pt/C electrocatalyst. Assembled in a zinc-air battery, a Co₃Fe₇@Co/Fe-SAC hybrid-based cell demonstrates a power density 1.8 times higher than the benchmark Pt/C-IrO₂-based one, and it is stable for 150 cycles galvanostatic charge/discharge. The superior device performance is attributed to the appealing intrinsic activity, the carbon shielding effect for anti-leaching, and the hierarchical porous networks for large accessibility of active sites and favorable mass transport. Theoretical calculations suggest that alloy nanoparticles significantly improved the intrinsic catalytic activity of Fe single-atom sites at the expense of slightly lowering the activity of Co single-atom sites. This work presents a versatile process for the mass production of efficient composite electrocatalysts and highlights the power of bimetal single-atom-based hybrids and hierarchically porous structures for ORR device performances.

Recent Progress of Non-Noble Metal Catalysts for Oxygen Electrode in Zn-Air Batteries: A Mini Review

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play crucial roles in energy conversion and storage devices. Particularly, the bifunctional ORR/OER catalysts are core components in rechargeable metal–air batteries, which have shown great promise in achieving "carbon emissions peak and carbon neutrality" goals. However, the sluggish ORR and OER kinetics at the oxygen cathode significantly hinder the performance of metal–air batteries. Although noble metal-based catalysts have been widely employed in accelerating the kinetics and improving the bifunctionality, their scarcity and high cost have limited their deployment in the market. In this review, we will discuss the ORR and OER mechanisms, propose the principles for bifunctional electrocatalysts design, and present the recent progress of the state-of-the-art bifunctional catalysts, with the focus on non-noble metal-based materials to replace the noble metal catalysts in Zn–air batteries. The perspectives for the future R&D of bifunctional electrocatalysts will be provided toward high-performance Zn–air batteries at the end of this paper.

Transition Metal (Co, Ni, Fe, Cu) Single-Atom Catalysts Anchored on 3D Nitrogen-Doped Porous Carbon Nanosheets as Efficient Oxygen Reduction Electrocatalysts for Zn-Air Battery

Exploring highly active and cost-efficient single-atom catalysts (SACs) for oxygen reduction reaction (ORR) is critical for the large-scale application of Zn-air battery. Herein, density functional theory (DFT) calculations predict that the intrinsic ORR activity of the active metal of SACs follows the trend of Co > Fe > Ni ≈ Cu, in which Co SACs possess the best ORR activity due to its optimized spin density. Guided by DFT calculations, four kinds of transition metal single atoms embedded in 3D porous nitrogen-doped carbon nanosheets (MSAs@PNCN, M = Co, Ni, Fe, Cu) are synthesized via a facile NaCl-template assisted strategy. The resulting MSAs@PNCN displays ORR activity trend in lines with the theoretical predictions, and the Co SAs@PNCN exhibits the best ORR activity (E_1/2  = 0.851 V), being comparable to that of Pt/C under alkaline conditions. X-ray absorption fine structure (XAFS) spectra verify the atomically dispersed Co-N₄ sites are the catalytically active sites. The highly active CoN₄ sites and the unique 3D porous structure contribute to the outstanding ORR performance of Co SAs@PNCN. Furthermore, the Co SAs@PNCN catalyst is employed as cathode in Zn-air battery, which can deliver a large power density of 220 mW cm^-2 and maintain robust cycling stability over 530 cycles.

Nickel-induced charge redistribution in Ni-Fe/Fe3C@nitrogen-doped carbon nanocage as a robust Mott-Schottky bi-functional oxygen catalyst for rechargeable Zn-air battery

Designing earth-abundant and advanced bi-functional oxygen electrodes for efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are extremely urgent but still ambiguous. Thus, metal-semiconductor nanohybrids were developed with functionally integrating ORR-active Ni species, OER-active Fe/Fe₃C components, and multifunctional N-doped carbon (NDC) support. Expectantly, the resulted NDC nanocage embedded with Ni-Fe alloy and Fe₃C particles, as assembled Mott-Schottky-typed catalyst, delivered a promoted half-wave potential of 0.904 V for ORR and a low overpotential of 315 mV at 10 mA/cm² for OER both in alkaline media, outperforming those of commercial Pt/C and RuO₂ counterparts. Most importantly, the optimized Ni-Fe/Fe₃C@NDC sample also afforded a peak power density of 267.5 mW/cm² with a specific capacity of 773.8 mAh/g_Zn and excellent durability over 80 h when used as the air electrode in rechargeable Zn-air batteries, superior to the state-of-the-art bi-functional catalysts. Ultraviolet photoelectron spectroscopy revealed that the introduction of Ni into the Fe/Fe₃C@NDC component could well manipulate the electronic structure of the designed electrocatalyst, leading to an effective built-in electric field established by the Mott-Schottky heterojunction to expedite the continuous interfacial charge-transfer and thus significantly promote the utilization of electrocatalytic active sites. Therefore, this work provides an avenue for the designing and developing robust and durable Mott-Schottky-typed bi-functional catalysts for promising energy conversion.

Mesoporous Single Crystals with Fe-Rich Skin for Ultralow Overpotential in Oxygen Evolution Catalysis

The oxygen evolution reaction (OER) is a key reaction in water splitting and metal-air batteries, and transition metal hydroxides have demonstrated the most electrocatalytic efficiency. Making the hydroxides thinner for more surface commonly fails to increase the active site number, because the real active sites are the edges. Up to now, the overpotentials of most state-of-the-art OER electrocatalysts at a current density of 10 mA cm^-2 (η₁₀ ) are still larger than 200 mV. Herein, a novel design of mesoporous single crystal (MSC) with an Fe-rich skin to boost the OER is shown. The edges around the mesopores provide lots of real active sites and the Fe modification on these sites further improves the intrinsic activity. As a result, an ultralow η₁₀ of 185 mV is achieved, and the turnover frequency based on Fe atoms is as high as 16.9 s^-1 at an overpotential of 350 mV. Moreover, the catalyst has an excellent catalytic stability, indicated by a negligible current drop after 10 000 cyclic voltammetry cycles. The catalyst enables Zn-air batteries to run stably over 270 h with a low charge voltage of 1.89 V. This work shows that MSC materials can provide new opportunities for the design of electrocatalysts.

Overdoping strategy for preparing of two-phase oxide electrocatalyst to boost oxygen evolution reaction

The oxygen evolution reaction is of great significance to the production of hydrogen from high efficiency electrolytic water, hydrogen oxygen fuel cell and other energy conversion devices, but there are many challenges such as high cost, low efficiency and poor stability of catalysts. Among non-precious metal catalysts, oxide has its unique advantages. We used overdoping strategy to prepare two-phase oxide electrocatalyst SrCo 0.9 Fe 0.05 Mo 0.35 O x (SCFM 0.35 ) containing double perovskite and Co3O4 with excellent OER electrocatalytic activity and stability in alkaline solution. It required an overpotential of 361.7 mV to reach a 10 mA cm -2 current density and its performance only degrades by 3.48% after 1000 CV cycles accelerated stability tests, whose electrochemical performance is superior to that of single-phase double perovskites and undoped perovskites. SrCo 0.9 Fe 0.1 O 3 (SCF) ordinary perovskite is doped with slightly molybdenum (Mo), and then the ordinary perovskite turns into double perovskite because of the polyvalence characteristics of Mo. When Mo is overdoped, Co 3 O 4 phase was precipitated while Mo entered perovskite phase. This process causes lattice distortion and makes the surface electronic structure benign changes. Furthermore, the microscopic morphology of the material surface and the valence state of cobalt element are changed, thereby improving the microenvironment of the electrochemical process.

Carbon Nanotubes Interconnected NiCo Layered Double Hydroxide Rhombic Dodecahedral Nanocages for Efficient Oxygen Evolution Reaction

Proper control of a 3d transition metal-based catalyst with advanced structures toward oxygen evolution reaction (OER) with a more feasible synthesis strategy is of great significance for sustainable energy-related devices. Herein, carbon nanotube interconnected NiCo layered double hydroxide rhombic dodecahedral nanocages (NiCo-LDH RDC@CNTs) were developed here with the assistance of a feasible zeolitic imidazolate framework (ZIF) self-sacrificing template strategy as a highly efficient OER electrocatalyst. Profited by the well-fined rhombic dodecahedral nanocage architecture, CNTs’ interconnected characteristic and structural feature of the vertically aligned nanosheets, the as-synthesized NiCo-LDH RDC@CNTs integrated large exposed active surface areas, enhanced electron transfer capacity and multidimensional mass diffusion channels, and thereby collaboratively afforded the remarkable electrocatalytic performance of the OER. Specifically, the designed NiCo-LDH RDC@CNTs exhibited a distinguished OER activity, which only required a low overpotential of 255 mV to reach a current density of 10 mA cm⁻² for the OER. For the stability, no obvious current attenuation was detected, even after continuous operation for more than 27 h. We certainly believe that the current extraordinary OER activity combined with the robust stability of NiCo-LDH RDC@CNTs enables it to be a great candidate electrocatalyst for economical and sustainable energy-related devices.

Constructing High Efficiency CoZnx Mn2-x O4 Electrocatalyst by Regulating the Electronic Structure and Surface Reconstruction

It is an effective strategy to develop novel electrocatalysts with controllable defects to enhance their electrocatalytic activity and stability. However, how to precisely design these catalysts on the atom scale remains very difficult. Herein, several vacancy-dependent CoZn_x Mn_2-x O₄ catalysts are prepared through tailoring the concentration of Zn ions. The in situ activation of the obtained products accelerates the surface reconstruction. The superior electrocatalytic performance can be ascribed to the formations of MOOH (Mn, Co) active species and abundant oxygen vacancies, which are comparable to noble IrO₂ and Pt/C catalysts. Zn-CoMn₂ O₄ -1.5 catalyst delivers a cell voltage of 1.63 V and long durability. Density functional theory calculations demonstrate that the appropriate Zn ion doping can improve the density states of p electron on the surface of catalysts significantly and benefit the d-band center closing to Fermi level, suggesting their high charge carrier density and low adsorption energy.

The potential of Co3O4 nanoparticles attached to the surface of MnO2 nanorods as cathode catalyst for single-chamber microbial fuel cell

A simple two-step hydrothermal method was used to prepare the cathode catalyst of microbial fuel cell (MFC). MnO₂@Co₃O₄ composite was successfully prepared by in-situ growth of nano-particle-like Co₃O₄ on nano-rod-like MnO₂. The hybrid products had (121), (310), (311), (400) and (511) crystal planes, rod-like and point-like structures were observed. MnO₂@Co₃O₄ nanohybrids were rich in a variety of metallic elements and provided rich electrochemically active sites. The maximum voltage of MnO₂@Co₃O₄-MFC was 425 mV, the maximum stabilization time was 4 d. The maximum output power was 475 mW/m², which was 2.24 times that of Co₃O₄-MFC (212 mW/m²) and 2.63 times of MnO₂-MFC (180 mW/m²). The rod-like structure of MnO₂ could effectively improve the ion flow efficiency and reduce the transfer resistance, and the point-like structure of Co₃O₄ can increase the specific surface area of the complex and provide more active sites.

Motivating borate doped FeNi layered double hydroxides by molten salt method toward efficient oxygen evolution

The incorporation of borate is a beneficial strategy to improve the catalytic activity of transition metal-based electrocatalyts for oxygen evolution reaction (OER). However, how to efficiently introduce borate has always been a challenge. Here, a facile and scalable molten salt method is developed to successfully dope borate into FeNi layered double hydroxides (FeB_i@FeNi LDH) for efficient OER. The molten salt method can not only promote the formation of evenly dispersed nano-pompous FeB_i precursor, thus providing the possibility to realize the direct doping of borate and the increase of mass, charge transfer and oxygen evolution active sites in FeNi LDH, but also promote the in-situ growth of FeB_i@FeNi LDH on the conductive iron foam, improvingconductivity and stability of the material. The results indicate that the synthesized FeB_i@FeNi LDH shows enhanced OER activity by delivering current densities of 10 and 100 mA cm^-2 at low overpotentials of 246 and 295 mV and showing a small Tafel slope of 56.48 mV dec^-1, benefiting from the optimization of geometric structure of active sites as well as the adjustment of electron density by borate doping especially in the case of molten salt. In addition, the sample can maintain durability at an industrial current density of 100 mA cm^-1 for 90 h. This work provides a new way for the construction of efficient catalysts using boron doping assisted by molten salt.

In situ coupling of Ag nanoparticles with high-entropy oxides as highly stable bifunctional catalysts for wearable Zn-Ag/Zn-air hybrid batteries

With the combination of the advantages of both Zn-Ag and Zn-air batteries, hybrid Zn-Ag/Zn-air batteries nevertheless suffer greatly from structural instability and activity degradation of the catalysts at the air electrodes. Herein, we introduce a scalable chemical dealloying procedure to synthesize mutually interacting and stable bifunctional catalysts, consisting of imbedded Ag nanoparticles for the oxygen reduction reaction (ORR) and quantitatively designed multicomponent high-entropy oxides (HEOs) for the oxygen evolution reaction (OER). The ORR performance and the Zn-Ag battery capacity can be precisely controlled by the content of Ag nanoparticles. Impressively, with a significantly low Ag content (∼9.13 wt%) in the bifunctional (AlNiCoFeCr)₃O₄/Ag, our hybrid Zn-Ag/Zn-air batteries using such catalysts are able to be continuously charged/discharged for more than 450 h and deliver a high energy density of 810 W h kg^-1. We expect that these stabilized noble metals in HEO nanocomposites may work as multifunctional electrocatalysts in many other energy conversion devices.

N- and O-doped hollow carbons constructed by self- and extrinsic activation for the oxygen reduction reaction and flexible zinc-air Batteries

Zinc-air batteries (ZAB), especially those assembled on flexible substrates, have attracted great research attention in electronics and wearable electronics. However, the air-cathode reaction-oxygen reduction reaction (ORR) has limited the development of ZAB technology. In this study, a hollow carbon catalyst, NOC-1000-1, was prepared by pyrolysis of a mixture of a N-enriched Zn/bispyrozolate-based metal-organic framework and urea to replace the labile Pt-based catalysts for ORR. The employment of sacrifical urea eliminated the requirement for complicated post-treatment compared to the template method. Combined with self-activation (Zn evaporation), the obtained carbon showed a micro- and mesopore-dominant hierarchical structure coexisting with some macropores. Moreover, the doped N and O species were also tailored in a preferable configuration for ORR by simply screening the pyrolysis conditions. Under the synergistic effect of the preferable N and O configurations and pore structure, the derived carbon catalyst displayed superior ORR activity of 0.977 V onset potential and 0.867 V half-wave potential; these values are slightly better than those of the 20% Pt/C benchmark catalyst (0.985 and 0.861 V, respectively). Flexible solid-state ZABs were further assembled by employing the derived carbon catalyst as an air-cathode, and they exhibited a higher peak power density of 100.92 mW cm^-2 than a 20% Pt/C-RuO₂ battery as well as previously reported similar batteries and very high stability for up to 30 h. The flexible solid-state ZABs could drive a red light-emitting diode and run a 130-type motor for hours, which indicates their promising applications in real-world technologies.

Interface Engineering of Heterogeneous CeO2-CoO Nanofibers with Rich Oxygen Vacancies for Enhanced Electrocatalytic Oxygen Evolution Performance

The development of highly efficient and cheap electrocatalysts for the oxygen evolution reaction (OER) is highly desirable in typical water-splitting electrolyzers to achieve renewable energy production, yet it still remains a huge challenge. Herein, we have presented a simple procedure to construct a new nanofibrous hybrid structure with the interface connecting the surface of CeO₂ and CoO as a high-performance electrocatalyst toward the OER through an electrospinning-calcination-reduction process. The resultant CeO₂-CoO nanofibers exhibit excellent electrocatalytic properties with a small overpotential of 296 mV at 10 mA cm^-2 for the OER, which is superior to many previously reported nonprecious metal-based and commercial RuO₂ catalysts. Furthermore, the prepared CeO₂-CoO nanofibers display remarkable long-term stability, which can be maintained for 130 h with nearly no attenuation of OER activity in an alkaline electrolyte. A combined experimental and theoretical investigation reveals that the excellent OER properties of CeO₂-CoO nanofibers are due to the unique interfacial architecture between CeO₂ and CoO, where abundant oxygen vacancies can be generated due to the incomplete matching of atomic positions of two parts, leading to the formation of many low-coordinated Co sites with high OER catalytic activity. This research provides a practical and promising opportunity for the application of heterostructured nonprecious metal oxide catalysts for high-efficiency electrochemical water oxidation.

Anchoring Sites Engineering in Single-Atom Catalysts for Highly Efficient Electrochemical Energy Conversion Reactions

Single-atom catalysts (SACs) have been at the frontier of research field in catalysis owing to the maximized atomic utilization, unique structures and properties. The atomically dispersed and catalytically active metal atoms are necessarily anchored by surrounding atoms. As such, the structure and composition of anchoring sites significantly influence the catalytic performance of SACs even with the same metal element. Significant progress has been made to understand structure-activity relationships at an atomic level, but in-depth understanding in precisely designing highly efficient SACs for the targeted reactions is still required. In this review, various anchoring sites in SACs are summarized and classified into five different types (doped heteroatoms, defect sites, surface atoms, metal sites, and cavity sites). Then, their impacts on catalytic performance are elucidated for electrochemical reactions based on their distance from the metal center (first coordination shell and beyond). Further, SACs anchored on two typical types of hosts, carbon- and metal-based materials, are highlighted, and the effects of anchoring points on achieving the desirable atomic structure, catalytic performance, and reaction pathways are elaborated. At last, insights and outlook to the SAC field based on current achievements and challenges are presented.

Low temperature scalable synthetic approach enabling high bifunctional electrocatalytic performance of NiCo2S4 and CuCo2S4 thiospinels

Ternary metal sulfides are currently in the spotlight as promising electroactive materials for high-performance energy storage and/or conversion technologies. Extensive research on metal sulfides has indicated that, amongst other factors, the electrochemical properties of the materials are strongly influenced by the synthetic protocol employed. Herein, we report the electrochemical performance of uncapped NiCo₂S₄ and CuCo₂S₄ ternary systems prepared via solventless thermolysis of the respective metal ethyl xanthate precursors at 200 and 300 °C. The structural, morphological and compositional properties of the synthesized nanoparticles were examined by powder X-ray diffraction (p-XRD), transmission electron microscopy (TEM), high-resolution TEM, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) techniques. Electrochemical studies indicate that NiCo₂S₄ nanoparticles synthesized at 300 °C exhibit superior energy storage characteristics with a high specific capacitance of ca. 2650 F g⁻¹ at 1 mV s⁻¹, as compared to CuCo₂S₄ nanoparticles, which showcased a specific capacitance of ca. 1700 F g⁻¹ at the same scan rate. At a current density of 0.5 A g⁻¹, NiCo₂S₄ and CuCo₂S₄ nanoparticles displayed specific capacitances of 1201 and 475 F g⁻¹, respectively. In contrast, CuCo₂S₄ nanoparticles presented a higher electrocatalytic activity with low overpotentials of 269 mV for oxygen evolution reaction (OER), and 224 mV for the hydrogen evolution reaction (HER), at 10 mA cm⁻². The stability of the catalysts was examined for 2000 cycles in which a negligible change in both OER and HER activities was observed.

A scalable solventless approach is employed to prepare NiCo₂S₄ and CuCo₂S₄ with bare surface for enhanced supercapacitance and water splitting. The particles exhibit good energy storage and electrocatalytic activity as well as stability.

Facile Synthesis of Carbon Cloth Supported Cobalt Carbonate Hydroxide Hydrate Nanoarrays for Highly Efficient Oxygen Evolution Reaction

Developing efficient and low-cost replacements for noble metals as electrocatalysts for the oxygen evolution reaction (OER) remain a great challenge. Herein, we report a needle-like cobalt carbonate hydroxide hydrate (Co(CO₃)_0.5OH·0.11H₂O) nanoarrays, which in situ grown on the surface of carbon cloth through a facile one-step hydrothermal method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations demonstrate that the Co(CO₃)_0.5OH nanoarrays with high porosity is composed of numerous one-dimensional (1D) nanoneedles. Owing to unique needle-like array structure and abundant exposed active sites, the Co(CO₃)_0.5OH@CC only requires 317 mV of overpotential to reach a current density of 10 mA cm⁻², which is much lower than those of Co(OH)₂@CC (378 mV), CoCO₃@CC (465 mV) and RuO₂@CC (380 mV). For the stability, there is no significant attenuation of current density after continuous operation 27 h. This work paves a facile way to the design and construction of electrocatalysts for the OER.

Anchoring Fe-N-C Sites on Hierarchically Porous Carbon Sphere and CNT Interpenetrated Nanostructures as Efficient Cathodes for Zinc-Air Batteries

Engineering efficient zinc-air batteries have attracted tremendous attention because of their essential role in the field of renewable energy systems. However, the sluggish reaction kinetics of the oxygen reduction reaction (ORR) at the air cathode impair the battery performance significantly. Recently, metal-N-C-based porous carbon nanoarchitectures have emerged as promising ORR electrocatalysts in zinc-air batteries. Herein, taking advantage of metal-organic complexation and mesoporous silica templates, we successfully anchor Fe-N-C sites on hierarchically porous carbon sphere and carbon nanotube interpenetrated nanostructures (Fe-N-C/HPCS@CNT) to serve as efficient cathodes for zinc-air batteries. Benefiting from its synergistic effects between the highly active Fe-N-C sites, ultrahigh surface areas, and unique hierarchically porous nanostructures, Fe-N-C/HPCS@CNT exhibits preferable ORR performance (E_1/2 = 0.873 V) compared to commercial Pt/C (E_1/2 = 0.841 V). Most importantly, when used as a cathode catalyst for homemade zinc-air batteries, Fe-N-C/HPCS@CNT exhibits gratifying peak power density (164.0 mW cm^-2), large specific capacity (762.0 mAh g^-1), superior long-term stability, extraordinary rate capability, and excellent charge/discharge performance. We believe that this report will not only offer new insights into the design of Fe-N-C-based catalysts but also promote the practical utilization of Fe-N-C-based cathodes for a wide range of energy applications.

Zn-Nx sites on N-doped carbon for aerobic oxidative cleavage and esterification of C(CO)-C bonds

Selective cleavage of C-C bonds is very important in organic chemistry, but remains challenging because of their inert chemical nature. Herein, we report that Zn/NC-X catalysts, in which Zn2+ coordinate with N species on microporous N-doped carbon (NC) and X denotes the pyrolysis temperature, can effectively catalyze aerobic oxidative cleavage of C(CO)-C bonds and quantitatively convert acetophenone to methyl benzoate with a yield of 99% at 100 °C. The Zn/NC-950 can be applied for a wide scope of acetophenone derivatives as well as more challenging alkyl ketones. Detail mechanistic investigations reveal that the catalytic performance of Zn/NC-950 can be attributed to the coordination between Zn2+ and N species to change the electronic state of the metal, synergetic effect of the Zn single sites with their surrounding N atoms, as well as the microporous structure with the high surface area and structural defects of the NC.

Integrating a metal framework with Co-confined carbon nanotubes as trifunctional electrocatalysts to boost electron and mass transfer approaching practical applications

A facile and large-scale construction of robust and inexpensive trifunctional self-supporting electrodes for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in metal-air batteries and water splitting is crucial but remains challenging. Herein, we report a direct and up-scalable all-solid-phase strategy for the synthesis of a porous three-dimensional electrode consisting of cobalt nanoparticles wrapped in nitrogen-doped carbon tubes (Co/N-CNTs), which are in situ planted onto the surface of a cobalt foam. The resultant Co/N-CNTs can directly serve as a self-supporting and adhesive-free electrode with excellent and durable catalytic performances for the ORR, OER and HER. The metal framework substrate with an open-pore architecture is favorable for electron and mass transfer and allows fast catalytic kinetics. More importantly, when used in Zn-air batteries and overall water splitting, the as-prepared Co/N-CNT electrode displays a remarkable performance, implying bright perspects for practical application.

Enhancing the electrocatalytic activity and stability of Prussian blue analogues by increasing their electroactive sites through the introduction of Au nanoparticles

Prussian blue analogues (PBAs) have been proven as excellent Earth-abundant electrocatalysts for the oxygen evolution reaction (OER) in acidic, neutral and alkaline media. Further improvements can be achieved by increasing their electrical conductivity, but scarce attention has been paid to quantify the electroactive sites of the electrocatalyst when this enhancement occurs. In this work, we have studied how the chemical design influences the specific density of electroactive sites in different Au-PBA nanostructures. Thus, we have first obtained and fully characterized a variety of monodisperse core@shell hybrid nanoparticles of Au@PBA (PBA of Ni^IIFe^II and Co^IIFe^II) with different shell sizes. Their catalytic activity is evaluated by studying the OER, which is compared to pristine PBAs and other Au-PBA heterostructures. By using the coulovoltammetric technique, we have demonstrated that the introduction of 5-10% of Au in weight in the core@shell leads to an increase in the electroactive mass and thus, to a higher density of active sites capable of taking part in the OER. This increase leads to a significant decrease in the onset potential (up to 100 mV) and an increase (up to 420%) in the current density recorded at an overpotential of 350 mV. However, the Tafel slope remains unchanged, suggesting that Au reduces the limiting potential of the catalyst with no variation in the reaction kinetics. These improvements are not observed in other Au-PBA nanostructures mainly due to a lower contact between both compounds and the Au oxidation. Hence, an Au core activates the PBA shell and increases the conductivity of the resulting hybrid, while the PBA shell prevents Au oxidation. The strong synergistic effect existing in the core@shell structure evidences the importance of the chemical design for preparing PBA-based nanostructures exhibiting better electrocatalytic performances and higher electrochemical stabilities.

Influence of the Amount of Carbon during the Synthesis of LaFe0.8Co0.2O3/Carbon Hybrid Material in Oxygen Evolution Reaction

The oxygen evolution reaction (OER) and the hydrogen evolution reaction occurred at the anode and cathode, which depends on the electronic structure, morphology, electrochemically active surface area, and charge-transfer resistance of the electrocatalyst. Transition metals like cobalt, nickel, and iron have better OER and oxygen reduction reaction activities. At the same time, transition-metal oxide/carbon hybrid has several applications in electrochemical energy conversion reactions. The rich catalytic site of transition metals and the excellent conductivity of carbon material make these materials as a hopeful electrocatalyst in OER. Carbon-incorporated LaFe_0.8Co_0.2O₃ was prepared by a simple solution combustion method for the development of the best performance of the electrocatalyst. The catalyst can deliver 10 mA/cm² current density at an overpotential of 410 mV with better catalytic stability. The introduction of carbon material improves the dispersion ability of the catalyst and the electrical conductivity. The Tafel slope and onset potential of the best catalyst are 49.1 mV/dec and 1.55 V, respectively.

Sulfate Ions Induced Concave Porous S-N Co-Doped Carbon Confined FeCx Nanoclusters with Fe-N4 Sites for Efficient Oxygen Reduction in Alkaline and Acid Media

To improve the catalytic activity of the catalysts, it is key to intensifying the intrinsic activity of active sites or increasing the exposure of accessible active sites. In this work, an efficient oxygen reduction electrocatalyst is designed that confines plentiful FeC_x nanoclusters with Fe-N₄ sites in a concave porous S-N co-doped carbon matrix, readily accessible for the oxygen reduction reaction (ORR). Sulfate ions react with the carbon derived from ZIF-8 at high temperatures, leading to the shrinkage of the carbon framework and then forming a concave structure with abundant macropores and mesopores with S incorporation. Such an architecture promotes the exposure of active sites and accelerates remote mass transfer. As a result, the catalyst (Fe/S-NC) with a large number of C-S-C, Fe-N₄ , and FeC_x nanoclusters presents impressive ORR activity and stability. In alkaline media, the half-wave potential of the best catalyst (Fe/S₂ -NC) is 0.91 V, which far exceeds that of commercial platinum carbon (0.85 V), while in acidic media the half-wave potential reaches 0.784 V, comparable to platinum carbon (0.812 V). Furthermore, for the zinc-air battery, the outstanding peak power density of Fe/S₂ -NC (170 mW cm^-2 ) superior to platinum carbon (108 mW cm^-2 ) also highlights its great application potential.

Hierarchically Assembling CoFe Prussian Blue Analogue Nanocubes on CoP Nanosheets as Highly Efficient Electrocatalysts for Overall Water Splitting

Efficient and durable electrocatalysts are highly desirable for overall water splitting. Herein, a facile strategy is demonstrated to rationally construct CoFe Prussian blue analogues (PBA)@CoP cube-on-sheet hierarchical structure by etching reaction with intermediated CoO to form PBA nanocubes. Benefitting from the heterostructured engineering, the as-synthesized CoFe PBA@CoP presents remarkable electrocatalytic performance in 1.0 m KOH, only requiring overpotentials of 100 mV for hydrogen evolution reaction (HER) and 171 mV for oxygen evolution reaction (OER) to reach the 10 mA cm^-2 current density with good stability. Extraordinarily enhanced electrocatalytic performance is ascribed to not only the rapid charge transfer of active species, but also the synergistic effect between each component to achieve tuned electronic structure and abundant electrocatalytic active sites. Especially, the assembled two-electrode cell using CoFe PBA@CoP as both cathode and anode delivers the current densities of 10 mA cm^-2 at a relatively low cell voltage of 1.542 V, outperforming most of low-cost bifunctional electrocatalysts reported to date. The controllable and versatile strategy will open up an avenue to prepare hybrid films for advanced electrochemical energy storage and conversion.

Coupling Hierarchical Ultrathin Co Nanosheets With N-Doped Carbon Plate as High-Efficiency Oxygen Evolution Electrocatalysts

The rational design of cost-effective and highly efficient catalysts for the oxygen evolution reaction (OER) is vastly desirable for advanced renewable energy conversion and storage systems. Tailoring the composition and architecture of electrocatalysts is a reliable approach for improving their catalytic performance. Herein, we developed hierarchical ultra-thin Co nanosheets coupled with N-doped carbon plate (Co-NS@NCP) as an efficient OER catalyst through a feasible and easily scalable NaCl template method. The rapid dissolution-recrystallization-carbonization synthesis process allows Co nanosheets to self-assemble into plenty of secondary building units and to distribute uniformly on N-doped carbon plate. Benefitting from the vertically aligned Co nanosheet arrays and hierarchical architecture, the obtained Co-NS@NCP possess an extremely high specific surface area up to 446.49 m2 g−1, which provides sufficient exposed active sites, excellent structure stability, and multidimensional mass transfer channels. Thus, the Co-NS@NCP affords remarkable electrocatalytic performance for OER in an alkaline medium with a low overpotential of only 278 mV at 10 mA cm−2, a small Tafel slope, as well as robust electrocatalytic stability for long-term electrolysis operation. The present findings here emphasize a rational and promising perspective for designing high-efficiency non-precious electrocatalysts for the OER process and sustainable energy storage and conversion system.

ZIF-derived "senbei"-like Co9S8/CeO2/Co heterostructural nitrogen-doped carbon nanosheets as bifunctional oxygen electrocatalysts for Zn-air batteries

The rational design and construction of the efficient and robust non-noble metal bifunctional oxygen electrocatalysts is of critical significance due to the attention given to reversible metal-air batteries. In this paper, we report novel two-dimensional "senbei"-like Co9S8/CeO2/Co-NC nitrogen-doped carbon nanosheets (Co9S8/CeO2/Co-NC) derived from a unique 2D Co/Ce bimetallic ZIF. The phase transition from 3D spherical Co-ZIF to 2D Co/Ce-ZIF was achieved through the introduction of Ce ions. Profiting from the successful construction of the unique Co9S8/CeO2 heterostructure and the synergetic effect of two components, the as-prepared Co9S8/CeO2/Co-NC exhibited excellent electro-performance in both the oxygen evolution reaction (Ej=10 = 1.60 V) and oxygen reduction reaction (E1/2 = 0.875 V). Furthermore, when used as a bifunctional air electrode for Zn-air batteries, Co9S8/CeO2/Co-NC reached a high peak power density of ≈164.24 mW cm-2 at a high current density of ≈351 mA cm-2 and displayed an outstanding cycling stability of more than 668 h at 5 mA cm-2. This research provides new guidelines for preparing hybrid materials from cobalt-based sulfide species and CeO2 for electrocatalysis and energy storage or other fields.

Bioinspired interfacial engineering of a CoSe2 decorated carbon framework cathode towards temperature-tolerant and flexible Zn-air batteries

A high-performance air electrode is essential for the successful application of flexible Zn-air batteries in wearable devices. However, endowing the electrode-electrolyte interface with high stability and fast electron/ion transportation is still a great challenge. Herein, we report a bioinspired interfacial engineering strategy to construct a cactus-like hybrid electrode comprising CoSe2 nanoparticles embedded in an N-doped carbon nanosheet arrays penetrated with carbon nanotubes (CoSe2-NCNT NSA). Associated with the synergistic effect of highly active CoSe2 nanoparticles and N-doped carbon moieties and a stable 3D interconnected CNT network, the obtained self-standing electrode exhibits satisfactory catalytic activities towards oxygen evolution/reduction and hydrogen evolution, as well as an enhanced electrode-electrolyte interaction/interface area, and thus delivers superior performance for flexible Zn-air batteries. Remarkably, the fabricated flexible Zn-air battery with this CoSe2-NCNT NSA cathode achieves a high peak power density (51.1 mW cm-2), considerable mechanical flexibility, and excellent durability in a wide temperature range of 0 to 40 °C. Furthermore, the assembled Zn-air batteries can efficiently power a water-splitting device that adopts the CoSe2-NCNT NSA as both the anode and cathode, demonstrating promising potential in energy conversion and portable electronic applications.

Interfacial La Diffusion in the CeO2/LaFeO3 Hybrid for Enhanced Oxygen Evolution Activity

The electrochemical oxygen evolution reaction (OER) is of great significance for energy conversion and storage. The hybrid strategy is attracting increasing interest for the development of highly active OER electrocatalysts. Regarding the activity enhancement mechanism, electron coupling between two phases in hybrids has been widely reported, but the interfacial elemental redistribution is rarely investigated. Herein, we developed a CeO₂/LaFeO₃ hybrid electrocatalyst for enhanced OER activity. Interestingly, a selective interfacial La diffusion from LaFeO₃ to CeO₂ was demonstrated by the electron energy loss spectra and elemental mapping. This redistribution of cations triggers the change of the chemical environment of interface elements for charge compensation because of the electroneutrality principle, which results in increased oxygen vacancies and high-valent Fe species that promote the OER electrocatalysis. This mechanism might be extended to other hybrid systems and inspire the design of more efficient electrocatalysts.

Pd nanoparticles loaded onto a TiO2–C heterostructure via a photochemical strategy for efficient oxygen reduction reaction

In this paper, we successfully reduced Pd to TiO2–C heterostructure (Pd/TiO2–C catalyst) by photochemical reduction method. The directional transfer of electrons from TiO2–C to Pd catalyst strengthens MA and improves the durability of ORR.