Facet-engineered TiO₂ nanomaterials reveal the role of water–oxide interactions in surface protonic conduction

Abstract

Water adsorption and surface protonic conduction have been investigated at 25 – 400 oC in wet (H2O and D2O) atmospheres on nanocrystalline TiO2 hydrothermally grown to a predominance of different...

Quantifiable models for surface protonic conductivity in porous oxides – case of monoclinic ZrO2

“…For our monoclinic ZrO 2 samples, however, there is no such secondary increase in conductivity. This is similar to the {101} facet of TiO 2 33 and our on-going work on undoped CeO 2 39 where it even increases less steeply above RHs of 60%. As our data do not extensively explore the region at RH > 60%, we refrain from analysing that region further and it is not part of Table 2.…”

“…, below 50 °C at p H 2 O = 0.03 bar, a 2 nd liquid-like physisorbed layer is expected with strong increase in conductivity as temperature decreases further, as observed for, e.g. , porous YSZ 15 and TiO 2 , 33 but this was not evidenced in this study of monoclinic ZrO 2 .…”

“…As the physisorbed layer builds, it expectedly gets more liquid-like and the physisorption enthalpy approaches that of pure liquid water. This gives rise to an additional strong increase in the surface protonic conductivity in many porous ceramics, 15,28 including some facets of TiO 2 33 as we approach RT and relative humidity (RH) surpasses 60%. For our monoclinic ZrO 2 samples, however, there is no such secondary increase in conductivity.…”

“…[25][26][27] TiO 2 has also been well studied [28][29][30] lately because protonic migration in adsorbed water appears to be central for the use of TiO 2 photocatalysts. 31,32 Recently, Kang et al 33 investigated the role of surface orientation on water adsorption and surface protonic conduction in anatase TiO 2 materials synthesised under conditions that favour different surface facets. They found by in situ FT-IR and conductivity measurements that simple {100} and {001} surfaces with accessible cations and anions favour dissociative chemisorption and the conductivity suggested that the subsequent physisorbed water layer was rigidly bonded and solid (ice-like).…”

Hydrophobic signature on TiO2 nanoparticles in liquid water

“…8 Relatively few attempts to probe TiO2 surfaces directly in aqueous environments have been reported so far. These included studies by inelastic and quasi-elastic neutron scattering (INS/QENS), [9][10][11] atomic force microscopy (AFM), 12 infrared spectroscopy (IR) 13 and sum frequency generation (SFG). 14 Although these studies indicated the existence of a layer of constrained water molecules with limited mobility at the nanoparticles perimeter, no further insights concerning reactivity could be elucidated.…”