Design of high-performance ion-doped CoP systems for hydrogen evolution:From multi-level screening calculations to experiment

Rational design of high-performance electrocatalysts for hydrogen evolution reaction(HER)is vital for future renewable energy systems.The incorporation of foreign metal ions into catalysts can be an effective approach to optimize its performance.However,there is a lack of systematic theoretical studies to reveal the quantitative relationships at the electronic level.Here,we develop a multi-level screening methodology to search for highly stable and active dopants for CoP catalysts.The density functional theory(DFT)calculations and symbolic regression(SR)were performed to investigate the relationship between the adsorption free energy(ΔG_(H^(*)))and 10 electronic parameters.The mathematic formulas derived from SR indicate that the difference of work function(ΔΦ)between doped metal and the acceptor plays the most important role in regulatingΔG_(H^(*)),followed by the d-band center(d-BC)of doped system.The descriptor of HER can be expressed asΔG_(H^(*))=1.59×√|0.188ΔΦ+d BC+0.120|1/2-0.166 with a high determination coefficient(R^(2)=0.807).Consistent with the theoretical prediction,experimental results show that the Al-CoP delivers superior electrocatalytic HER activity with a low overpotential of75 m V to drive a current density of 10 mA cm^(-2),while the overpotentials for undoped CoP,Mo-CoP,and V-CoP are 206,134,and 83 m V,respectively.The current work proves that theΔΦis the most significant regulatory parameter ofΔG_(H^(*))for ion-doped electrocatalysts.This finding can drive the discovery of high-performance ion-doped electrocatalysts,which is crucial for electrocatalytic water splitting.

Preparation of erbium ion-doped TiO2 films and the study of their photocatalytic activity under simulated solar light

A series of erbium ion-doped TiO2（Er^3＋-TiO2） films were prepared by a sol-gel dip/spin coating method, and the effect of the dosage of erbium ion（0-2.0 mol%）, the films coating layers（1-5 layers）, and calcination temperature（400-700 ℃） on the film structure and photocatalytic activity were investigated in detail. The films were characterized by means of X-ray diffraction（XRD）, scanning electron microscopy（SEM）, thermal analysis（TG-DTG） and UV-Vis diffusive reflectance spectra（DRS）. The results showed that the films were composed of anatase, and no other TiO2 phases（rutile and brookite）. With the increase of the erbium ion dosage, the crystal size decreased. Erbium ion doping could enhance the thermal stability of TiO2 and inhibit the increase of the crystallite size. Meanwhile doping of erbium ions gave rise to three typical absorption peaks within the range of visible light（400-700 nm）, locating at 490, 523, and 654 nm, attributed to the transition of 4 f electrons. The higher calcination temperature led to higher crystallinity and bigger crystal grains. The photocatalytic performance of the films was evaluated by degradation of methyl orange solution under simulated solar light. The highest quality film we prepared was with 4 layers, 1.0 mol% dosage of erbium ion, and the calcination temperature of 500 ℃. With this film,the degradation percentage of 7.8 mg/L methyl orange solution was up to 53.3% under simulated solar light after 6 h photoreaction.

Ce^(3+)ion-doped α-NaYF_4 single crystal for UV laser

A Ce^（3＋）tion-doped α-Na YF_4 single crystal of high quality is grown successfully by an improved flux Bridgman method under the conditions of taking the chemical raw composition of Na F：KF：YF_3：CeF_3 in the molar ratio of30∶18∶48∶4, where the KF is shown to be an effective assistant flux. The x ray diffraction, absorption spectra,excitation spectra, and emission spectra of the Ce^（3＋）t-doped α-Na YF_4 single crystal are measured to investigate the phase and optical properties of the single crystals. The absorption spectrum of the Ce^（3＋）t：α-Na YF_4 shows a strong band that peaks at the wavelength of 300 nm. The emission spectrum of the Ce^（3＋）t：α-Na YF_4 emits an intense ultraviolet（UV） band at the wavelength of 332 nm under the excitation of 300 nm light. Two separated luminous bands of 330 and 350 nm, which correspond to the transitions 5d → 2F25∕2and 5d → F7∕2, can be obtained by Gauss fitting. The strong emission intensity at the UV band and the excellent optical transmission in the range of UV wavelengths indicate that Ce^（3＋）t：α-Na YF_4 single crystals can be considered as a promising material for UV lasers.

Effect of metal ion-doping on characteristics and photocatalytic activity of Ti02 nanotubes for removal of humic acid from water

The effect of ion-doping on TiO2 nanotubes were investigated to obtain the optimal TiO2 nanotubes for the effective decomposition of humic acids （HA） through O3/UV/ion-doped TiO2 process. The experimental results show that changing the calcination temperature, which changed the weight fractions of the anatase phase, the average crystallite sizes, the Brunauer-Emmett-Teller sur- face area, and the energy band gap of the catalyst, affected the photocatalytic activity of the catalyst. The ionic radius, valence state, and configuration of the dopant also affected the photocatalytic activity. The photocatalytic activities of the catalysts on HA removal increased when Ag＋, AP＋, Cu2＋, Fe3＋, V5 ＋, and Zn2＋ were doped into the TiO2 nanotubes, whereas such activities decreased as a result of Mn2＋- and Ni2＋-doping. In the presence of 1.0 at.% Fe3＋- doped TiO2 nanotubes calcined at 550℃, the removal efficiency of HA was 80% with a pseudo-first-order rate constant of 0.158 min-. Fe3＋ in TiO2 could increase the generation of OH, which could remove HA. However, Fe3＋ in water cannot function as a shallow trapping site for electrons or holes.

Controlling multiphoton excited energy transfer from Tm^(3+) to Yb^(3+) ions by a phase-shaped femtosecond laser field

The ability to control the energy transfer in rare-earth ion-doped luminescent materials is very important for various related application areas such as color display, bio-labeling, and new light sources. Here, a phase-shaped femtosecond laser field is first proposed to control the transfer of multiphoton excited energy from Tm^(3+) to Yb^(3+) ions in co-doped glass ceramics. Tm^(3+) ions are first sensitized by femtosecond laser-induced multiphoton absorption, and then a highly efficient energy transfer occurs between the highly excited state Tm^(3+) sensitizers and the ground-state Yb^(3+) activators. The laser peak intensity and polarization dependences of the laser-induced luminescence intensities are shown to serve as proof of the multiphoton excited energy transfer pathway.The efficiency of the multiphoton excited energy transfer can be efficiently enhanced or completely suppressed by optimizing the spectral phase of the femtosecond laser with a feedback control strategy based on a genetic algorithm. A(1+2) resonance-mediated three-photon excitation model is presented to explain the experimental observations. This study provides a new way to induce and control the energy transfer in rare-earth ion-doped luminescent materials, and should have a positive contribution to the development of related applications.