RESUMEN
Designing bifunctional low-cost photo-assisted electrocatalysts for converting solar and electric energy into hydrogen energy remains a huge challenge. Herein, a heterojunction (Fe cluster modified Co9 S8 loaded on carbon nanotubes, Co9 S8 -Fe@CNT) for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is demonstrated. Benefiting from the good electronic conductivity and spatial confinement of the carbon skeleton, as well as the electronic structure regulation of the Fe cluster, Co9 S8 -Fe@CNT exhibits excellent catalytic performance with a low overpotential of 150 mV for OER and 135 mV for HER at 10 mA cm-2 . Upon light irradiation, holes and electrons are generated in the valence band and conduction band of the Co9 S8 , respectively. Part of the charges are transferred to the interface to facilitate the catalytic reaction, while the remaining are transferred by the electrode. When working as a bifunctional catalyst for overall water splitting, the performance can reach 1.33 V at under light conditions, which is significantly better than 1.52 V in a dark environment. Theoretical calculations revealed lowered Gibbs free energy (∆GH *) of the heterojunction with the effect of Fe modification of Co9 S8 . This work sheds a new light in designing novel photoelectrochemical materials to convert solar and electric energy into chemical energy.
RESUMEN
Preparing MoS2 -based materials with reasonable structure and catalytic activity to enhance the sluggish kinetics of lithium polysulfides (LiPSs) conversion is of great significance for Li-S batteries (LSBs) but still remain a challenge. Hence, hollow nanotubes composed of N-doped ultrathin MoS2 nanosheets (N-MoS2 NHTs) are fabricated as efficient S hosts for LSBs by using CdS nanorods as a sacrifice template. Characterization and theoretical results show that the template effectively inhibits the excessive growth of MoS2 sheets, and N doping expands the interlayer spacing and modulates the electronic structure, thus accelerating the mass/electron transfer and enhancing the LiPSs adsorption and transformation. Benefiting from the merits, the N-MoS2 NHTs@S cathode exhibits an excellent initial capacity of 887.8 mAh g-1 and stable cycling performances with capacity fading of only 0.0436% per cycle at 1.0 C (500 cycles). Moreover, even at high S loading that of 7.5 mg cm-2 , the N-MoS2 NHTs@S cathode also presents initial excellent areal capacity of 7.80 mAh cm-2 at 0.2 C. This study offers feasible guidance for designing advanced MoS2 -based cathode materials in LSBs.
RESUMEN
The large-scale hydrogen production and application through electrocatalytic water splitting depends crucially on the development of highly efficient, cost-effective electrocatalysts for oxygen evolution reaction (OER), which, however, remains challenging. Here, a new electrocatalyst of trimetallic Fe-Co-Ni hydroxide (denoted as FeCoNiOx Hy ) with a nanotubular structure is developed through an enhanced Kirkendall process under applied potential. The FeCoNiOx Hy features synergistic electronic interaction between Fe, Co, and Ni, which not only notably increases the intrinsic OER activity of FeCoNiOx Hy by facilitating the formation of *OOH intermediate, but also substantially improves the intrinsic conductivity of FeCoNiOx Hy to facilitate charge transfer and activate catalytic sites through electrocatalyst by promoting the formation of abundant Co3+ . Therefore, FeCoNiOx Hy delivers remarkably accelerated OER kinetics and superior apparent activity, indicated by an ultra-low overpotential potential of 257 mV at a high current density of 200 mA cm-2 . This work is of fundamental and practical significance for synergistic catalysis related to advanced energy conversion materials and technologies.
RESUMEN
The rational design and synthesis of highly efficient electrocatalysts for oxygen evolution reaction (OER) is of critical importance to the large-scale production of hydrogen by water electrolysis. Here, we develop a bimetallic, synergistic, and highly efficient Co-Fe-P electrocatalyst for OER, by selecting a two-dimensional metal-organic framework (MOF) of Co-ZIF-L as the precursor. The Co-Fe-P electrocatalyst features pronounced synergistic effects induced by notable electron transfer from Co to Fe, and a large electrochemical active surface area achieved by organizing the synergistic Co-Fe-P into hierarchical nanosheet arrays with disordered grain boundaries. Such features facilitate the generation of abundant and efficiently exposed Co3+ sites for electrocatalytic OER and thus enable Co-Fe-P to deliver excellent activity (overpotential and Tafel slope as low as 240 mV and 36 mV dec-1, respectively, at a current density of 10 mA cm-2 in 1.0 M KOH solution). The Co-Fe-P electrocatalyst also shows great durability by steadily working for up to 24 h. Our work thus provides new insight into the development of highly efficient electrocatalysts based on nanoscale and/or electronic structure engineering.
RESUMEN
The exploration of efficient bifunctional electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) under alkaline conditions is an importantway to promote the development of electrolytic water technology. Herein, the reduced graphene oxide-supported MoO42- modified amorphous cobalt metaphosphate cubes (a-Co(PO3)2/MoO4/rGO) as bifunctional OER/HER catalyst is prepared by anion exchange and phosphating, using the Prussian blue analogue (PBA) as a precursor. The resulting composite exhibits the low overpotentials (η) that of 290 and 50 mV for OER and HER in 1.0 M KOH solution at 10 mA cm-2, respectively. The electrochemical test and density functional theory (DFT) results reveal that the MoO42--modified optimizes the adsorption/desorption energy of H* of Co(PO3)2, thus enhance the HER activity. Benefiting from efficient HER and OER performances, an efficient and stable alkaline water electrolysis operation using a-Co(PO3)2/MoO4/rGO used as bifunctional catalyst can be carried out, which can deliver a current density (j) of 20 mA cm-2 at 1.65 V cell voltage and work continuously for 24 h.
RESUMEN
Antibiotic resistance is an imminent threat to human health, requiring the development of effective alternate antibacterial agents. One such alternative includes nanoparticle (photo)catalysts that are good at producing reactive oxygen species (ROS). Herein, we report the design and preparation of nitrogen-doped carbon dots functionalized with atomically dispersed copper centers by Cu-N coordination (Cu/NCD) that exhibit apparent antibacterial activity toward Gram-negative Escherichia coli (E. coli) under photoirradiation. The growth of E. coli cells is found to be markedly inhibited by Cu/NCD under 365 nm photoirradiation, whereas no apparent inhibition is observed in the dark or with the copper-free carbon dots alone. This is ascribed to the prolonged photoluminescence lifetime of Cu/NCD that facilitates the separation of photogenerated electron-hole pairs and ROS formation. The addition of tert-butyl alcohol is found to completely diminish the antimicrobial activity, suggesting that hydroxyl radicals are responsible for microbial death. Consistent results are obtained from fluorescence microscopic studies using CellROX green as the probe. Similar bactericidal behaviors are observed with Gram-positive Staphylococcus epidermidis (S. epidermidis). The copper content within the carbon material is optimized at a low loading of 1.09 wt %, reducing the possibility of toxic copper-ion leaching. Results from this study highlight the significance of carbon-based nanocomposites with isolated metal species as potent antimicrobial reagents.