Promoting hydrogen-evolution activity and stability of perovskite oxides via effectively lattice doping of molybdenum

Electrocatalysts are the most compelling objectives in realizing highly efficient renewable energy conversion and storage applications. Rational doping is an effective strategy for the development of cost-effective perovskite oxides with high electrochemical performance. In this study, we report facilely prepared molybdenum (Mo)-doped SrCo0.70Fe0.30O3-δ perovskites such as SrCo0.7Fe0.25Mo0.05O3-δ (SCFM0.05) and SrCo0.7Fe0.20Mo0.10O3-δ (SCFM0.10) for boosting the hydrogen evolution reaction (HER) activity and stability. Among them, SCFM0.05 delivers a promising overpotential of ∼323 mV at the current density of 10 mA cmdisk^-2 and keeps almost stable for 5 h and after accelerated 1000 cycles. The promoted HER activity of SCFM0.05 regarding the decreased overpotential, increased catalytic current density, and improved charge transfer kinetics, might originate from the combined effects of distortion of octahedral coordination, low oxygen vacancy/high oxidation state of Co, abundant lattice oxygen and highly oxidative oxygen species, long B–O length, and strong OH− adsorption compared to the un-doped counterpart. We ascribe the enhanced operational stability to the formation of a low concentration of oxygen vacancy that stabilizes the crystal structure of Mo-doped SrCo0.7Fe0.3O3-δ and prevents the surface from Sr leaching/surface amorphization. These findings suggest that tuning perovskite oxide using a redox-inactive dopant featured with high valence state may provide further avenues to HER optimization.This research is supported by the National Natural Science Foundation of China (No. 51702125 & No. 21808080), Pearl River S&T Nova Program of Guangzhou (No. 201806010054), Fundamental Research Funds for the Central Universities (No. 21616301), and the China Postdoctoral Science Foundation (No. 2017M620401)

Promoting surface reconstruction of NiFe layered double hydroxide for enhanced oxygen evolution

A dynamic surface reconstruction of oxide electrocatalysts in alkaline media is widely observed especially for layered double hydroxide (LDH), but little is known about how to promote the reconstruction toward desired surfaces for improved oxygen evolution reaction (OER). Here, surface reconstruction of NiFe LDH nanosheets is successfully induced to a higher degree via in situ sulfur doping than that by natural electrochemical activation. Theoretical calculations, operando Raman, and various ex situ characterizations reveal the S anion-induced effect can lower the energy barrier and facilitate the phase transformation into highly active S-doped oxyhydroxides. The generated S-NixFeyOOH can optimize the intermediate adsorption and facilitate the OER kinetics. The reconstructed S-oxyhydroxides catalyst presents superior OER activity and long-term durability compared to undoped ones. This work provides a structure–composition–activity relationship during the in situ surface restructuring of NiFe LDH pre-catalysts.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)Submitted/Accepted versionThis research is financially supported by the National Natural Science Foundation of China (51872124), Agency for Science, Technology, and Research (A*STAR), Singapore by AME Individual Research Grants (A1983c0026), the Ministry of Education of China (6141A02022516), and the Ministry of Education, Singapore, under its Academic Research Fund Tier 1 (RG125/21). H.L. is thankful for the financial support from the China Scholarship Council (No.202106780011)

Highly Active and Stable Cobalt-Free Hafnium-doped SrFe_0.9Hf_0.1O_3−δ Perovskite Cathode for Solid Oxide Fuel Cells

Sluggish oxygen reduction reaction (ORR) kinetics and chemical instability of cathode materials hinder the practical application of solid oxide fuel cells (SOFCs). Here we report a Co-free Hf-doped SrFe_0.9Hf_0.1O_3−δ (SFHf) perovskite oxide as a potential cathode focusing on enhancing the ORR activity and chemical stability. We find that SFHf exhibits a high ORR activity, stable cubic crystal structure, and improved chemical stability toward CO₂ poisoning compared to undoped SrFeO_3−δ. The SFHf cathode has a polarization area-specific resistance as low as 0.193 Ω cm² at 600 °C in a SFHf|Sm_0.2Ce_0.8O_1.9 (SDC)|SFHf symmetrical cell and has a maximum power density as high as 1.94 W cm^–2 at 700 °C in an anode-supported fuel cell (Ni+(ZrO₂)_0.92(Y₂O₃)_0.08 (YSZ)|YSZ|SDC|SFHf). The ORR activity maintains stable for a period of 120 h in air and in CO₂-containing atmosphere. The attractive ORR activity is attributed to the moderate concentration of oxygen vacancy and electrical conductivity, as well as the fast oxygen kinetics at the operation temperature. The improved chemical stability is related to the doping of the redox-inactive Hf cation in the Fe site of SrFeO_3−δ by decreasing oxygen vacancy concentration and increasing metal–oxygen bond energy. This work proposes an effective strategy in the design of highly active and stable cathodes for SOFCs

Carboxymethyl cellulose-grafted graphene oxide for efficient antitumor drug delivery

A drug delivery system based on carboxymethyl cellulose-grafted graphene oxide loaded by methotrexate (MTX/CMC-GO) with pH-sensitive and controlled drug-release properties was developed in this work. CMC was grafted on graphene oxide by ethylenediamine through hydrothermal treatment. CMC serves as a pH-sensitive trigger, while CMC-GO serves as a drug-carrying vehicle due to the curved layer and large plain surface. Different amounts of drugs could be loaded into CMC-GO nanocarriers by control of the original amount of drug/carrier ratios. Additionally, low cytotoxicity against NIH-3T3 cells and low in vivo toxicity was observed. In vivo tumor growth inhibition assays showed that MTX/CMC-GO demonstrated superior antitumor activity than free MTX against HT-29 cells. Moreover, prolonged survival time of mice was observed after MTX/CMC-GO administration. The MTX/CMC-GO drug delivery system has a great potential in colon cancer therapy

Highly Active and Stable Cobalt-Free Hafnium-doped SrFe_0.9Hf_0.1O_3−δ Perovskite Cathode for Solid Oxide Fuel Cells

Sluggish oxygen reduction reaction (ORR) kinetics and chemical instability of cathode materials hinder the practical application of solid oxide fuel cells (SOFCs). Here we report a Co-free Hf-doped SrFe_0.9Hf_0.1O_3−δ (SFHf) perovskite oxide as a potential cathode focusing on enhancing the ORR activity and chemical stability. We find that SFHf exhibits a high ORR activity, stable cubic crystal structure, and improved chemical stability toward CO₂ poisoning compared to undoped SrFeO_3−δ. The SFHf cathode has a polarization area-specific resistance as low as 0.193 Ω cm² at 600 °C in a SFHf|Sm_0.2Ce_0.8O_1.9 (SDC)|SFHf symmetrical cell and has a maximum power density as high as 1.94 W cm^–2 at 700 °C in an anode-supported fuel cell (Ni+(ZrO₂)_0.92(Y₂O₃)_0.08 (YSZ)|YSZ|SDC|SFHf). The ORR activity maintains stable for a period of 120 h in air and in CO₂-containing atmosphere. The attractive ORR activity is attributed to the moderate concentration of oxygen vacancy and electrical conductivity, as well as the fast oxygen kinetics at the operation temperature. The improved chemical stability is related to the doping of the redox-inactive Hf cation in the Fe site of SrFeO_3−δ by decreasing oxygen vacancy concentration and increasing metal–oxygen bond energy. This work proposes an effective strategy in the design of highly active and stable cathodes for SOFCs

Bacteria-Adsorbed Palygorskite Stabilizes the Quaternary Phosphonium Salt with Specific-Targeting Capability, Long-Term Antibacterial Activity, and Lower Cytotoxicity

In order to extend the antibacterial time of quaternary phosphonium salt in bacteria, palygorskite (PGS) is used as the carrier of dodecyl triphenyl phosphonium bromide (DTP), and a DTP-PGS hybrid is prepared. Antibacterial performance of this novel hybrid is investigated for both Gram-positive and Gram-negative bacteria. The results show that the DTP could be absorbed on the surface of PGS which had bacteria-adsorbed capability. The DTP-PGS hybrid, combining the advantages of PGS and DTP, display specific-targeting capability, long-term antibacterial activity, and lower cytotoxicity, suggesting the great potential application as PGS-based antibacterial powder