Fine-tuning nanoflower-like Fe/Co hybrids with high content oxyhydroxide accelerating oxygen evolution kinetics.

Iron hydroxide (FeOOH) is a potential active component in iron-based electrocatalysts for water electrolysis. However, its catalytic performance is constrained by its slow oxygen evolution reaction (OER) kinetics. Herein, we synthesized a nanoflower-like FeCo-hydro(oxy)oxides composite with tunable Fe/Co ratios (Fex-Coy) on nickel foam (NF) via a one-step electrodeposition technique. This method allows for precise control over the morphology and composition of the hybrid nanoflowers. The optimized Fe9-Co1 discloses favorable OER performance with a low overpotential of 222 mV at 50 mA cm-2 and demonstrates good stability exceeding 60 h at 10 mA cm-2. Further, an assembled Fe9-Co1(+)||Pt/C(-) dual-electrode configuration achieves a low cell voltage of 1.73 V at the current density of 100 mA cm-2 for water splitting, with long-term stability for 70 h and minimal degradation. Studies indicate that the distinctive nanoflower morphology of Fe9-Co1 enhances active site exposure, while both FeOOH and reconstructed CoOOH serve as catalytic centers, contributing to the observed OER performance. This work introduces a facile approach for synthesizing OER electrocatalysts, underscoring the role of the high-valence state of Fe/Co as active sites in the OER process.

Synergistic vacancy engineering of Co/MnO@NC catalyst for superior oxygen reduction reaction in liquid/solid zinc-air batteries.

The pursuit of efficient and economically viable catalysts for liquid/solid-state zinc-air batteries (ZABs) is of paramount importance yet presents formidable challenge. Herein, we synthesized a vacancy-rich cobalt/manganese oxide catalyst (Co/MnO@NC) stabilized on a nitrogen-doped mesoporous carbon (NC) nanosphere matrix by leveraging hydrothermal and high-temperature pyrolysis strategy. The optimized Co/MnO@NC demonstrates fast reaction kinetics and large limiting current densities comparable to commercial Pt/C in alkaline electrolyte for oxygen reduction reaction (ORR). Moreover, the Co/MnO@NC serves as an incredible cathode material for both liquid and flexible solid-state ZABs, delivering impressive peak power densities of 217.7 and 63.3 mW cm-2 and robust long-term stability (459 h), outperforming the state-of-the-art Pt/C and majority of the currently reported catalysts. Research indicates that the superior performance of the Co/MnO@NC catalyst primarily stems from the synergy between the heightened electrical conductivity of metallic Co and the regulatory capacity of MnO on adsorbed oxygen intermediates. In addition, the abundance of vacancies regulates the electronic configuration, and superhydrophilicity facilitates efficient electrolyte diffusion, thereby effectively ensuring optimal contact between the active site and reactants. Besides, the coexisting NC layer avoids the shedding of active sites, resulting in high stability. This work provides a viable approach for designing and advancing high-performance liquid/solid-state ZABs, highlighting the great potential of energy storage technology.

Geometric and Electronic Engineering in Co/VN Nanoparticles to Boost Bifunctional Oxygen Electrocatalysis for Aqueous/Flexible Zn-Air Batteries.

Modulating metal-metal and metal-support interactions is one of the potent tools for augmenting catalytic performance. Herein, highly active Co/VN nanoparticles are well dispersed on three-dimensional porous carbon nanofoam (Co/VN@NC) with the assistance of dicyandiamide. Studies certify that the consequential disordered carbon substrate reinforces the confinement of electrons, while the coupling of diverse components optimizes charge redistribution among species. Besides, theoretical analyses confirm that the regulated electron configuration can significantly tune the binding strength between the active sites and intermediates, thus optimizing reaction energy barriers. Therefore, Co/VN@NC exhibits a competitive potential difference (ΔE, 0.65 V) between the half-wave potential of ORR and OER potential at 10 mA cm-2, outperforming Pt/C+RuO2 (0.67 V). Further, catalyst-based aqueous/flexible ZABs present superior performances with peak power densities of 156 and 85 mW cm-2, superior to Pt/C-based counterparts (128 and 73 mW cm-2). This research provides a pivotal foundation for the evolution of bifunctional catalysts in the energy sector.

Synergistic Co-N/V-N dual sites in N-doped Co3V2O8 nanosheets: pioneering high-efficiency bifunctional electrolysis for high-current water splitting.

Developing affluent dual-metal active sites bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential to achieve large-scale water electrolysis, whereas still remains challenging. Herein, a novel nitrogen-doped cobalt-vanadium oxide with abundant Co-N and V-N dual active sites supported on nickel foam (N-Co3V2O8@NF) is constructed by a controllable impregnation-thermal nitridation strategy. The staggered nanosheet structure ensures optimal exposure of active sites. More importantly, N doping effectively regulates the electronic structure of the metal centers and induces the formation of Co-N and V-N dual active sites, which is conducive to improving the conductivity and hydrophilicity, thus synergistically enhancing the electrocatalytic efficiency. Consequently, the optimized N-Co3V2O8@NF exhibits prominent HER (63 mV@10 mA cm-2) and OER (256 mV@10 mA cm-2) activities, surpassing most contemporary bifunctional electrocatalysts. In practical application, the assembled N-Co3V2O8@NF(+/-) electrolyzer consistently achieved ultra-low cell voltages of 1.97 and 2.03 V at 500 and 1000 mA cm-2, respectively, superior to the benchmark RuO2@NF(+) || Pt/C@NF(-) and showcasing robust durability. This paves the way for its prospective adoption in industrial water electrolysis applications.

Mn-Doped Zn Metal-Organic Framework-Derived Porous N-Doped Carbon Composite as a High-Performance Nonprecious Electrocatalyst for Oxygen Reduction and Aqueous/Flexible Zinc-Air Batteries.

Developing low-cost, efficient, and stable oxygen reduction reaction (ORR) electrocatalysts is crucial for the commercialization of energy conversion devices such as metal-air batteries. In this study, we report a Mn-doped Zn metal-organic framework-derived porous N-doped carbon composite (30-ZnMn-NC) as a high-performance ORR catalyst. 30-ZnMn-NC exhibits excellent electrocatalytic activity, demonstrating a kinetic current density of 9.58 mA cm-2 (0.8 V) and a half-wave potential of 0.83 V, surpassing the benchmark Pt/C and most of the recently reported non-noble metal-based catalysts. Moreover, the assembled zinc-air battery with 30-ZnMn-NC demonstrates high peak power densities of 207 and 66.3 mW cm-2 in liquid and flexible batteries, respectively, highlighting its potential for practical applications. The excellent electrocatalytic activity of 30-ZnMn-NC is attributed to its unique porous structure, the strong electronic interaction between metal Zn/Mn and adjacent N-doped carbon, as well as the bimetallic Mn/Zn-N active sites, which synergistically promote faster reaction kinetics. This work offers a controllable design strategy for efficient electrocatalysts with porous structures and bimetallic active sites, which can significantly enhance the performance of energy conversion devices.

Synergistic Promotion of Large-Current Water Splitting through Interfacial Engineering of Hierarchically Structured CoP-FeP Nanosheets with Rich P Vacancies.

The development of hydrogen evolution reaction (HER) catalysts with high performance under large current density is still a challenge. Introducing P vacancies in heterostructure is an appealing strategy to enhance HER kinetics. This study investigates a CoP-FeP heterostructure catalyst with abundant P vacancies (Vp-CoP-FeP/NF) on nickel foam (NF), which was prepared using dipping and phosphating treatment. The optimized Vp-CoP-FeP catalyst exerted prominent HER catalytic capability, requiring an ultra-low overpotential (58 mV @ 10 mA cm-2 ) and displaying robust durability (50 h @ 200 mA cm-2 ) in 1.0 M KOH solution. Furthermore, the catalyst demonstrated superior overall water splitting activity as cathode, demanding only cell voltage of 1.76 V at 200 mA cm-2 , outperforming Pt/C/NF(-) || RuO2 /NF(+) . The catalyst's outstanding performance can be attributed to the hierarchical structure of porous nanosheets, abundant P vacancies, and synergistic effect between CoP and FeP components, which promote water dissociation and H* adsorption and desorption, thereby synergically accelerating HER kinetics and enhancing HER activity. This study demonstrates the potential of HER catalysts with phosphorus-rich vacancies that can work under industrial-scale current density, highlighting the importance of developing durable and efficient catalysts for hydrogen production.

Interfacial engineering of Co5.47N/Mo5N6 nanosheets with rich active sites synergistically accelerates water dissociation kinetics for Pt-like hydrogen evolution.

The development of highly efficient hydrogen evolution electrocatalysts with platinum-like activity requires precise control of active sites through interface engineering strategies. In this study, a heterostructured Co5.47N/Mo5N6 catalyst (CoMoNx) on carbon cloth (CC) was synthesized using a combination of dip-etching and vapor nitridation methods. The rough nanosheet surface of the catalyst with uniformly distributed elements exposes a large active surface area and provides abundant interface sites that serve as additional active sites. The CoMoNx was found to exhibit exceptional hydrogen evolution reaction (HER) activity with a low overpotential of 44 mV at 10 mA cm-2 and exceptional stability of 100 h in 1.0 M KOH. The CoMoNx(-)||RuO2(+) system requires only 1.81 V cell voltage to reach a current density of 200 mA cm-2, surpassing the majority of previously reported electrolyzers. Density functional theory (DFT) calculations reveal that the strong synergy between Co5.47N and Mo5N6 at the interface can significantly reduce the water dissociation energy barrier, thereby improving the kinetics of hydrogen evolution. Furthermore, the rough nanosheet architecture of the CoMoNx catalyst with abundant interstitial spaces and multi-channels enhances charge transport and reaction intermediate transportation, synergistically improving the performance of the HER for water splitting.

Electronic Modulation and Mechanistic Study of Ru-Decorated Porous Cu-Rich Cuprous Oxide for Robust Alkaline Hydrogen Oxidation and Evolution Reactions.

Rational design of high-efficiency and viable electrocatalysts is essential in overcoming the bottleneck of sluggish alkaline hydrogen oxidation/evolution reaction (HOR/HER) kinetics. In this study, a metal-organic framework-derived strategy for constructing a Pt-free catalyst with Ru clusters anchored on porous Cu-Cu2 O@C is proposed. The designed Ru/Cu-Cu2 O@C exhibits superior HOR performance, with a mass activity of 2.7 mA µ g R u - 1 ${{{\rm \mu }{\rm g}}_{{\rm R}{\rm u}}^{-1}}$ at 50 mV, which is about 24 times higher than that of state-of-the-art Pt/C (0.11 mA µ g P t - 1 ${{{\rm \mu }{\rm g}}_{{\rm P}{\rm t}}^{-1}}$ ). Significantly, Ru/Cu-Cu2 O@C also displays impressive HER performance by generating 26 mV at 10 mA cm-2 , which exceeds the majority of documented Ru-based electrocatalysts. Systematic characterization and density functional theory (DFT) calculations reveal that efficient electron transfer between Ru and Cu species results in an attenuated hydrogen binding energy (HBE) of Ru and an enhanced hydroxy binding energy (OHBE) of Cu2 O, together with an optimized H2 O adsorption energy with Cu2 O as the H2 O*-capturing site, which jointly facilitates HOR and HER kinetics.

Co4S3 grafted 1 T-phase dominated WS2 ultrathin nanosheet arrays for highly efficient overall water splitting in alkaline media.

Developing the earth-abundant transition metal-based bifunctional electrocatalysts for water splitting and renewable energy devices has attracted much attention. Herein, we report a 1 T-WS2 in ultrathin nanosheet arrays grafted with Co4S3 on conductive carbon cloth (CC) (1 T-Co4S3-WS2/CC) through a feasible in-situ growth and vulcanization. The optimized 1 T-Co4S3-WS2/CC catalyst exhibits an impressive electrocatalytic activity and remarkable stability with the oxygen/hydrogen evolution reaction (OER/HER: 278/75 mV for 10 mA cm-2). It also showed the small Tafel slope values of 61.7 and 58.4 mV dec-1, respectively. Additionally, the 1 T-Co4S3-WS2/CC(-/+) achieved 1.59 V@10 mA cm-2 in alkaline media superior to the most previously reported non-precious metal electrocatalysts. The outstanding performance could be attributed to the synergy between heterostructures of Co4S3 and 1 T-WS2 modifying the electronic structure to accelerate water splitting kinetics. Thus, this work presents a rational design of scalable, high-efficiency, stable water splitting electrocatalysts based on WS2.

Oxygen vacancy-rich N-doped carbon encapsulated BiOCl-CNTs heterostructures as robust electrocatalyst synergistically promote oxygen reduction and Zn-air batteries.

The development of non-precious metal catalysts for oxygen reduction reactions (ORR) is vital for promising clean energy technologies such as fuel cells, and zinc-air batteries. Herein, we present a stepwise synthesis of N-doped and carbon encapsulated BiOCl-CNTs heterostructures. Electrocatalytic ORR studies show that the optimized catalyst has a high half-wave potential (E1/2) of 0.85 V (vs. RHE), large limiting current density (-5.34 mA cm-2@0.6 V) in alkaline medium, and nearly perfect 4e- reduction characteristics, even surpassing commercial Pt/C. Meanwhile, the catalyst has exceptional durability (above 97.5 % after 40000 s) and strong resistance towards methanol poisoning. The good ORR activity also results in high-performance zinc-air batteries with a specific capacity (724 mAh g-1@10 mA cm-2), a high open-circuit potential of 1.51 V and a peak power density of 170.7 mW cm-2, as well as an ultra-long charge-discharge cycle stability (155 h), comparable with the Pt/C catalyst. The catalytic mechanism reveals that the excellent electrocatalytic performance originates from the synergistic effect of N doping, oxygen vacancies, and BiOCl sites.

Engineering cobalt nitride nanosheet arrays with rich nitrogen defects as a bifunctional robust oxygen electrocatalyst in rechargeable Zn-air batteries.

Developing high-activity bifunctional oxygen electrocatalysts to overcome the sluggish 4e- kinetics is an urgent challenge for rechargeable metal-air batteries. Here, we prepared a CoN nanosheet catalyst with rich nitrogen defects (CoN-Nd) through solvothermal and low-temperature nitridation. Notably, the study finds for the first time that only Co LDH materials can be mostly converted to CoN-Nd under the same nitriding conditions relative to different Co-based precursors. Experiments indicate that the constructed CoN-Nd catalyst exhibits preeminent electrocatalytic activities for both oxygen evolution reaction (η10 = 243 mV) and oxygen reduction reaction (JL = 5.2 mA cm-2). Moreover, the CoN-Nd-based Zinc-air battery showed a large power density of 120 mW cm-2 and robust stability over 260 cycles, superior to the state-of-art Pt/C + RuO2. The superior performance is attributed to a large number of defects formed by the disordered arrangement of local atoms on the catalyst that facilitate the formation of more active sites, and alternate array-like structures thereof improving electrolyte diffusion and gas emission.

Interface Engineering of Needle-Like P-Doped MoS2 /CoP Arrays as Highly Active and Durable Bifunctional Electrocatalyst for Overall Water Splitting.

Developing a bifunctional water splitting catalyst with high efficiency and low cost are crucial in the electrolysis water industry. Here, we report a rational design and simple preparation method of MoS2 -based bifunctional electrocatalyst on carbon cloth (CC). The optimized P-doped MoS2 @CoP/CC catalyst presents low overpotentials for the hydrogen (HER) and oxygen evolution reactions (OER) of 64 and 282 mV in alkaline solution as well as 72 mV HER overpotential in H2 SO4 at a current density of 10 mA cm-2 . Furthermore, P-MoS2 @CoP/CC as a bifunctional catalyst delivered relatively low cell voltages of 1.83 and 1.97 V at high current densities of 500 and mA cm-2 in 30 % KOH. The two-electrode system showed a remarkable stability for 30 h, even outperformed the benchmark RuO2 ||Pt/C catalyst. The excellent electrochemical performance can be credited to the unique microstructure, high surface area, and the synergy between metal species. This study presents a possible alternative for noble metal-based catalysts to overcome the challenges of industrial applications.

Template synthesis of two-dimensional ternary nickel-cobalt-nitrogen co-doped porous carbon film: Promoting the conductivity and more active sites for oxygen reduction.

Rational design of a stable, highly active non-precious metal-based electrocatalysts for oxygen reduction reaction (ORR) is vitally important for industrial application of fuel cells technology. As a potential alternative of Pt/C catalyst, two-dimensional (2D) porous carbon materials are widely investigated due to the highly accessible surface area and active sites, wherein carbon films doped with a plurality of metals and non-metal elements are rarely reported due to an uncontrollable synthesis process. Here, a bi-metallic (NiCo alloy nanoparticles) and nonmetallic (N) co-doped porous carbon film (Ni-Co-N@CF) is fabricated by a simple controllable and scalable strategy comprising the synthesis of NiCo alloy nanoparticles, modification of organic molecules, and high-temperature carbonization process. The optimized Ni-Co-N@CF catalyst shows an excellent ORR electrocatalytic activity with a larger electrochemically active surface area (2.31 m2 g-1), a higher half-wave potential (0.86 V) and a lower diffusion limited current density (-4.43 mA cm-2) than all the prepared control catalysts. Moreover, the designated catalyst also exhibits high durability and superior methanol tolerance in alkaline media, significantly better than the commercial Pt/C (20 wt%). The superior ORR performance is attributed to the synergetic interactions of ternary doping of Ni/Co/N in the 2D film skeleton, which not only greatly enhances conductivity but also provides more Co-N active sites.