Building highly active hybrid double-atom sites in C_(2)N for enhanced electrocatalytic hydrogen peroxide synthesis

Two-electron(2 e^(-))oxygen reduction reaction(ORR)shows great promise for on-site electrochemical synthesis of hydrogen peroxide(H_(2)O_(2)).However,it is still a great challenge to design efficient electrocatalysts for H_(2)O_(2)synthesis.To address this issue,the logical design of the active site by controlling the geometric and electronic structures is urgently desired.Therefore,using density functional theory(DFT)computations,two kinds of hybrid double-atom supported on C_(2)N nanosheet(RuCu@C_(2)N and PdCu@C_(2)N)are screened out and their H_(2)O_(2)performances are predicted.PdCu@C_(2)N exhibits higher activity for H_(2)O_(2)synthesis with a lower overpotential of 0.12 V than RuCu@C_(2)N(0.59 V),Ru_(3)Cu(110)facet(0.60 V),and PdCu(110)facet(0.54 V).In aqueous phase,the adsorbed O_(2)is further stabilized with bulk H_(2)0 and the thermodynamic rate-determining step of 2 e^(-) ORR change.The activation barrier on PdCu@C_(2)N is 0.43 eV lower than the one on RuCu@C_(2)N with 0.68 eV.PdCu@C_(2)N is near the top of 2 e^(-) ORR volcano plot,and exhibits high selectivity of H_(2)O_(2.)This work provides guidelines for designing highly effective hybrid double-atom electrocatalysts(HDACs)for H_(2)O_(2)synthesis.

A first-principles study of reaction mechanism over carbon decorated oxygen-deficient TiO_(2) supported Pd catalyst in direct synthesis of H_(2)O_(2)

The choice of support is one of the most significant components in the direct synthesis of H_(2)O_(2).Aiming to improvement of activity and selectivity of H_(2)O_(2) on Pd/TiO_(2) surface,we systematically investigated the important elementary steps on Pd/TiO_(2)-Vo@C,Pd/TiO_(2)-Vo,Pd/TiO_(2)-2 Vo,Pd/TiO_(2),and Pd/C using the first-principles calculations.The Bader charge analysis and charge density difference of O_(2) adsorption elucidate the relationship between the electronic distribution and chemisorption energy.The effective barrier analysis further enables to quantitatively estimate the reactivity of H_(2)O_(2) and H2O.We demonstrate unambiguously that the selectivity of H2O formation is boosted as the oxygen vacancy concentration raised.Moreover,the introduction of C into a TiO_(2) with appropriate oxygen vacancies can slightly reduce the effective barrier for H_(2)O_(2) formation and increase the effective barrier for H2O formation leading to a higher activity and selectivity of H_(2)O_(2) formation.Our finding suggests that carbon-doped oxygen vacancy TiO_(2) supported Pd is potential alternative catalyst compared with the Pd/TiO_(2).

Tuning the ratio of Bi/Bi_(2)O_(3)in Bi/PNC nanosheet for highefficiency electrosynthesis hydrogen peroxide

Electrocatalytic two-electron oxygen reduction reaction(2e-ORR)is a promising method for producing green and sustainable H_(2)O_(2)but lacks high selectivity and yields electrocatalysts.And it is critical to develop catalysts that meet industrial demands.Herein,we report the different ratios of Bi0/Bi^(3+)supported on a phosphorus,nitrogen,and carbon nanosheet(Bi/PNC),which can reduce O_(2) to H_(2)O_(2)with high selectivity(up to 97.75%at 0.4 VRHE)in 0.1 M KOH electrolyte and retain 97%selectivity even after 100 h electrolysis.Then a homemade flow-cell system was built for electrocatalytic production of H_(2)O_(2)under an O_(2) atmosphere using an improved gas diffusion electrode.The Bi/PNC-4 can achieve a high H_(2)O_(2)yield of 2.76 mol·gcatalyst^(-1)·h^(-1)(alkaline),5.29 mol·gcatalyst^(-1)·h^(-1)(neutral),and 3.50 mol·gcatalyst^(-1)·h^(-1)(acid)in universal pH conditions.The in-situ generated H_(2)O_(2)can function as a degradation agent for efficiently degrading pesticides and antibiotics.The outstanding selectivity and activities are attributed to the synergistic effects of Bi0 and Bi^(3+)that promote proton-coupled reduction of O_(2) to OOH^(*)(ΔGOOH^(*)=4.27 eV),and the formation of H_(2)O_(2).The fast yield of H_(2)O_(2)on Bi/PNC catalysts in flow-cell provides a promising path of electrocatalytic 2e-ORR for practical H_(2)O_(2)production.

Optimizing strain response in lead-free(Bi_(0.5)Na_(0.5))TiO_(3)-BaTiO_(3)-NaNbO_(3)solid solutions via ferroelectric/(non-)ergodic relaxor phase boundary engineering

Lead-free bismuth sodium titanate(Bi_(0.5)Na_(0.5))TiO_(3)(BNT)and related solid solutions are potential piezoelectric materials for such applications as actuators and transducers if their excellent strain responses and piezoelectric properties can be optimized.In this work,a large strain response of 0.61%is achieved in lead-free(0.94-x%)(Bi_(0.5)Na_(0.5))TiO_(3)-0.06BaTiO_(3)-x%NaNbO_(3)(x=0 e6,BNT-6BT-xNN)ceramics with the composition of x=3.5 in a pseudo-cubic structure.Coexistence of ferroelectric(FE)and relaxor(RE)domain structures is observed in all the unpoled ceramics and the enhanced strain response is believed to be related to the evolution of the ergodic relaxor(ER)and non-ergodic(NR)states thanks to the substitution of antiferroelectric NN.BNT-6BT-3.5NN is a critical composition near the FE/NR/ER phase boundary close to room temperature(RT)and its high strain response arises from a synergistic combination of a reversible electric-field-induced phase transition and an active domain switching in the mixed NR/ER state.This work provides new insights into the dynamic interplay between mesoscopic domains and macroscopic electrical properties in the BNT-based piezoceramics.

Orientation dependence on piezoresponse of lead-free piezoelectric sodium bismuth titanate epitaxial thin films

Lead-free piezoelectric sodium bismuth titanate((Bi0.5Na0.5)TiO3,BNT)thin films were epitaxially grown onto(001)-,(110)-,and(111)-oriented Nb:SrTiO3(STO)single crystal substrates prepared by sol-gel processing.Highly oriented growth in(001),(110),and(111)BNT thin films was obtained in this work benefiting from the lattice match between the BNT film and the STO substrate.The different growth models in thin films with various orientations result in various surface morphologies dependent on the film orientation.The piezoresponse of the BNT thin films was represented exhibiting a strong orientation dependence that(110)>(001)>(111).This is contributed by the various domain switching contribution related to the crystal symmetry and polarization distribution in the three oriented thin films.

A hybrid bacterium with tumor-associated macrophage polarization for enhanced photothermal-immunotherapy

Remodeling the tumor microenvironment through reprogramming tumor-associated macrophages(TAMs) and increasing the immunogenicity of tumors via immunogenic cell death(ICD) have been emerging as promising anticancer immunotherapy strategies.However,the heterogeneous distribution of TAMs in tumor tissues and the heterogeneity of the tumor cells make the immune activation challenging.To overcome these dilemmas,a hybrid bacterium with tumor targeting and penetration,TAM polarization,and photo thermal conversion capabilities is developed for improving antitumor immunotherapy in vivo.The hybrid bacteria(B.b@QDs) are prepared by loading Ag;S quantum dots(QDs) on the Bifidobacterium bifidum(B.b) through electrostatic interactions.The hybrid bacteria with hypoxia targeting ability can effectively accumulate and penetrate the tumor tissues,enabling the B.b to fully contact with the TAMs and mediate their polarization toward M1 phenotype to reverse the immunosuppressive tumor microenvironment.It also enables to overcome the intratumoral heterogeneity and obtain abundant tumor-associated antigens by coupling tumor penetration of the B.b with photo thermal effect of the QDs,resulting in an enhanced immune effect.This strategy that combines B.b-triggered TAM polarization and QD-induced ICD achieved a remarkable inhibition of tumor growth in orthotopic breast cancer.