Herein, we highlight redox‐inert Zn2+ in spinel‐type oxide (ZnXNi1−XCo2O4) to synergistically optimize physical pore structure and increase the formation of active species on the catalyst surface. ...The presence of Zn2+ segregation has been identified experimentally and theoretically under oxygen‐evolving condition, the newly formed VZn−O−Co allows more suitable binding interaction between the active center Co and the oxygenated species, resulting in superior ORR performance. Moreover, a liquid flow Zn–air battery is constituted employing the structurally optimized Zn0.4Ni0.6Co2O4 nanoparticles supported on N‐doped carbon nanotube (ZNCO/NCNTs) as an efficient air cathode, which presents remarkable power density (109.1 mW cm−2), high open circuit potential (1.48 V vs. Zn), excellent durability, and high‐rate performance. This finding could elucidate the experimentally observed enhancement in the ORR activity of ZnXNi1−XCo2O4 oxides after the OER test.
The outstanding electrocatalytic performance of Zn0.4Ni0.6Co2O4/NCNTs towards ORR/OER is validated, presenting remarkable rate capability and durability in liquid‐flow Zn–air batteries. A dual‐reinforcement mechanism in the Zn–Ni–Co ternary spinel is also proposed. Zn0.4Ni0.6Co2O4/NCNTs exhibits extreme durability and electrochemically enhanced properties, enabling its application in practical rechargeable zinc–air batteries.
Transition‐metal oxides as electrocatalysts for the oxygen evolution reaction (OER) provide a promising route to face the energy and environmental crisis issues. Although palmeirite oxide A2Mo3O8 as ...OER catalyst has been explored, the correlation between its active sites (tetrahedral or octahedral) and OER performance has been elusive. Now, magnetic Co2Mo3O8@NC‐800 composed of highly crystallized Co2Mo3O8 nanosheets and ultrathin N‐rich carbon layer is shown to be an efficient OER catalyst. The catalyst exhibits favorable performance with an overpotential of 331 mV@10 mA cm−2 and 422 mV@40 mA cm−2, and a full water‐splitting electrolyzer with it as anode catalyst shows a cell voltage of 1.67 V@10 mA cm−2 in alkaline. Combined HAADFSTEM, magnetic, and computational results show that factors influencing the OER performance can be attributed to the tetrahedral Co sites (high spin, t23e4), which improve the OER kinetics of rate‐determining step to form *OOH.
Magnetic Co2Mo3O8@NC‐800 composed of single‐crystal Co2Mo3O8 and ultrathin nitrogen‐rich carbon was synthesized to uncover its OER active sites (Td Co2+ or Oh Co2+). Electrochemical data, magnetism data, and computations suggest that the Td Co2+ atoms (high spin, t23e4) in Co2Mo3O8 act as active sites facilitating the rate‐determining step, forming *OOH to promote the reaction kinetics for OER.
Bimetallic cobalt‐based spinel is sparking much interest, most notably for its excellent bifunctional performance. However, the effect of Fe3+ doping in Co3O4 spinel remains poorly understood, mainly ...because the surface state of a catalyst is difficult to characterize. Herein, a bifunctional oxygen electrode composed of spinel Co2FeO4/(Co0.72Fe0.28)Td(Co1.28Fe0.72)OctO4 nanoparticles grown on N‐doped carbon nanotubes (NCNTs) is designed, which exhibits superior performance to state‐of‐the‐art noble metal catalysts. Theoretical calculations and magnetic measurements reveal that the introduction of Fe3+ ions into the Co3O4 network causes delocalization of the Co 3d electrons and spin‐state transition. Fe3+ ions can effectively activate adjacent Co3+ ions under the action of both spin and charge effect, resulting in the enhanced intrinsic oxygen catalytic activity of the hybrid spinel Co2FeO4. This work provides not only a promising bifunctional electrode for zinc–air batteries, but also offers a new insight to understand the Co‐Fe spinel oxides for oxygen electrocatalysis.
A bifunctional oxygen electrode composed of hybrid spinel Co2FeO4 nanoparticles grown on N‐doped carbon nanotubes is a promising candidate for zinc–air batteries. Theoretical calculations and magnetic measurements reveal that the introduction of Fe cations into the Co3O4 network causes Co 3d electron delocalization and spin‐state transition, resulting in enhanced catalytic activity of the as‐prepared spinel Co2FeO4.
Covalent organic frameworks (COF) possess a robust and porous crystalline structure, making them an appealing candidate for energy storage. Herein, we report an exfoliated polyimide COF composite ...(P‐COF@SWCNT) prepared by an in situ condensation of anhydride and amine on the single‐walled carbon nanotubes as advanced anode for potassium‐ion batteries (PIBs). Numerous active sites exposed on the exfoliated frameworks and the various open pathways promote the highly efficient ion diffusion in the P‐COF@SWCNT while preventing irreversible dissolution in the electrolyte. During the charging/discharging process, K+ is engaged in the carbonyls of imide group and naphthalene rings through the enolization and π‐K+ effect, which is demonstrated by the DFT calculation and XPS, ex‐situ FTIR, Raman. As a result, the prepared P‐COF@SWCNT anode enables an incredibly high reversible specific capacity of 438 mA h g−1 at 0.05 A g−1 and extended stability. The structural advantage of P‐COF@SWCNT enables more insights into the design and versatility of COF as an electrode.
We prepare a polyimide covalent organic framework composite anode by effective in‐situ condensation of anhydride and amine on the surface of single‐walled carbon nanotubes. The construction of the conductive network accelerates the transport of electron. Dual electroactive sites in the framework, carbonyls and aromatic naphthalene rings, could store more potassium ions by the enolization and π‐K+ effect.
Impossible voltage plateau regulation for the cathode materials with fixed active elemental center is a pressing issue hindering the development of Na‐superionic‐conductor (NASICON)‐type ...Na3V2(PO4)2F3 (NVPF) cathodes in sodium‐ion batteries (SIBs). Herein, a high‐entropy substitution strategy, to alter the detailed crystal structure of NVPF without changing the central active V atom, is pioneeringly utilized, achieving simultaneous electronic conductivity enhancement and diffusion barrier reduction for Na+, according to theoretical calculations. The as‐prepared carbon‐free high‐entropy Na3V1.9(Ca,Mg,Al,Cr,Mn)0.1(PO4)2F3 (HE‐NVPF) cathode can deliver higher mean voltage of 3.81 V and more advantageous energy density up to 445.5 Wh kg−1, which is attributed by the diverse transition‐metal elemental substitution in high‐entropy crystalline. More importantly, high‐entropy introduction can help realize disordered rearrangement of Na+ at Na(2) active sites, thereby to refrain from unfavorable discharging behaviors at low‐voltage region, further lifting up the mean working voltage to realize a full Na‐ion storage at the high voltage plateau. Coupling with a hard carbon (HC) anode, HE‐NVPF//HC SIB full cells can deliver high specific energy density of 326.8 Wh kg−1 at 5 C with the power density of 2178.9 W kg−1. This route means the unlikely potential regulation in NASICON‐type crystal with unchangeable active center becomes possible, inspiring new ideas on elevating the mean working voltage for SIB cathodes.
A high‐entropy effect is delicately introduced into fluorophosphate cathode for sodium‐ion batteries by in situ partial substitution of active V central atom, preparing a high‐entropy carbon‐free Na3V1.9(Ca,Mg,Al,Cr,Mn)0.1(PO4)2F3 cathode, suppressing the occurrence of detrimental phase transition process in the low‐voltage region, and further lifting up the mean working voltage of pristine Na3V2(PO4)2F3, enhancing sodium storage behavior, rate capability, and cycle performance.
One of the most effective ways to cope with the problems of global warming and the energy shortage crisis is to develop renewable and clean energy sources. To achieve a carbon‐neutral energy cycle, ...advanced carbon sequestration technologies are urgently needed, but because CO2 is a thermodynamically stable molecule with the highest carbon valence state of +4, this process faces many challenges. In recent years, electrochemical CO2 reduction has become a promising approach to fix and convert CO2 into high‐value‐added fuels and chemical feedstock. However, the large‐scale commercial use of electrochemical CO2 reduction systems is hindered by poor electrocatalyst activity, large overpotential, low energy conversion efficiency, and product selectivity in reducing CO2. Therefore, there is an urgent need to rationally design highly efficient, stable, and scalable electrocatalysts to alleviate these problems. This minireview also aims to classify heterogeneous nanostructured electrocatalysts for the CO2 reduction reaction (CDRR).
Change for the better: Recent research on 0D, 1D, 2D, and multi‐component nanostructured materials for heterogeneous electrocatalytic CO2 conversion is summarized and discussed. The challenges and development prospects of nanostructured materials for CO2 conversion are also presented.
Heterostructured catalysts show outstanding performance in electrochemical reactions owing to their beneficial interfacial properties. However, the rational design of heterostructured catalysts with ...the desired interfacial properties and charge‐transfer characteristics is challenging. Herein, we developed a SrMn3O6−x‐SrMnO3 (SMOx‐SMO) heterostructure through epitaxial growth, which demonstrated excellent electrocatalyst performance for the oxygen reduction reaction (ORR). The formation of high‐valence Mn3+/4+ is beneficial for promoting a positive shift in the position of the d‐band center, thereby optimizing the adsorption and desorption of ORR intermediates on the heterojunction surface and resulting in improved catalytic activity. When SMOx‐SMO was applied as an air‐electrode catalyst in a rechargeable zinc‐air battery, a high output voltage and power density was achieved, with performance comparable to a battery prepared with Pt/C‐IrO2 air‐electrode catalysts, albeit with much better cycling stability.
An epitaxially grown SrMn3O6−x‐SrMnO3 heterostructure has been developed for the oxygen reduction reaction (ORR). Owing to the effect of interfacial chemistry on ORR performance, the formation of high‐valence Mn3+/4+ is beneficial in promoting the positive shift of the d‐band center, thereby optimizing the adsorption and desorption of ORR intermediates on the heterojunction surface and improving catalytic activity.
In order to clarify the characteristics of anaerobic ammonia oxidizing (ANAMMOX) sludge and the succession rule of bacteria based on particle size differentiation, the performance change and ...microbial community structure of ANAMMOX floc sludge during the formation of particles in the reaction system of a high ammonia-nitrogen biofilter were studied. The results indicated that the specific activity (SAA) and tolerance of the ANAMMOX granular sludge (AnGS) were significantly improved by increasing the particle size, and the SAA of R4(>4.75 mm) was up to 426.8 mg·(g·d)
, but it also had adverse effects on mass transfer. The results of the high-throughput sequencing showed that dynamic changes between bacterial genera were common. When the particle size was less than 4.75 mm, the increase in particle size strengthened the stability of the bacterial flora, the ammonia oxidizing bacteria (AOB) with more flocs were eliminated, and the nitrogen removal ratio gradually stabilized. R3 (2.8-4.75 mm) exhibited the most s
Iridium-catalyzed boron-hydrogen bond insertion reactions of trimethylamine-borane and sulfoxonium ylides have been demonstrated, furnishing α-boryl ketones in moderate to excellent yields in most ...cases (51 examples; up to 84%). This practical and scalable insertion reaction showed broad substrate scope, high functional-group compatibility and could be applied in late-stage modification of structurally complex drug compounds. Further synthetic applications were also demonstrated.
Iridium-catalyzed boron-hydrogen bond insertion reactions of trimethylamine-borane and sulfoxonium ylides have been demonstrated, furnishing α-boryl ketones in moderate to excellent yields in most cases (51 examples; up to 84%).
Developing cost-effective and stable Pt-free electrocatalysts for the oxygen reduction reaction (ORR) is now the key issue for the large-scale application of zinc-air batteries. Here, we present a ...simple charge modulation strategy to synthesize Co
2+
-activated spinel CoMn
2
O
4
supported self-catalysis derived nitrogen-doped carbon nanotubes (CoMn
2
O
4
/NCNTs@Ni). Associated with the formation of high valence Mn
3.4+
over the octahedral site of CoMn
2
O
4
, the corresponding oxygen binding energy can be effectively tuned to greatly enhance the activity of ORR, further revealed by the density functional theory calculations. Benefiting from the highly conductive CoMn
2
O
4
-NCNTs-Ni electron transport channels and high valence Mn
3.4+
, the CoMn
2
O
4
/NCNTs@Ni catalyst exhibits excellent oxygen electrocatalytic activity (the limiting-current density was 5.51 mA cm
−2
) and stability (the current density remained at 86.80% within 24 h), with much lower ORR overpotentials than Mn
3
O
4
/NCNTs@Ni (the limiting-current density was 5.35 mA cm
−2
and the current density remained at 71.63% within 13 h). The as-obtained CoMn
2
O
4
/NCNTs@Ni as a cathode can further assemble a zinc-air battery, which delivers an open-circuit potential of 1.46 V, even close to that of Pt/C (1.50 V), and excellent stability (charge-discharge stably for 238 h). This charge modulation strategy provides a new way to design and explore highly active, durable, and cost-effective catalysts for renewable energy conversion and storage.
The optimized CoMn
2
O
4
/NCNTs@Ni with high valence Mn
3.4+
as the catalytic site center, combined with the spinel-NCNTs-Ni electron transport channels jointly promote the electrocatalytic activity and successfully applied in zinc-air battery.
