Limits...
Transient Behavior of Ni@NiO x Functionalized SrTiO 3 in Overall Water Splitting

View Article: PubMed Central - PubMed

ABSTRACT

Transients in thecomposition of Ni@NiOx core–shellco-catalysts deposited on SrTiO3 arediscussed on the basis of state-of-the-art continuous analysis ofphotocatalytic water splitting, and post-XPS and TEM analyses. Theformation of excessive hydrogen (H2:O2 ≫2) in the initial stages of illumination demonstrates oxidation ofNi(OH)2 to NiOOH (nickel oxyhydroxide), with the lattercatalyzing water oxidation. A disproportionation reaction of Ni andNiOOH, yielding Ni(OH)2 with residual embedded Ni, occurswhen illumination is discontinued, which explains repetitive transientsin (excess) hydrogen and oxygen formation when illumination is reinitiated.

No MeSH data available.


HRTEM images and corresponding FFT results of the (a,d)as-prepared,(b,e) illuminated, and (c,f) regenerated Ni@NiOx SrTiO3 composite material. The observed changesin morphology and composition of the Ni@NiOx co-catalysts during overall water splitting are also schematicallyindicated.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5384480&req=5

fig4: HRTEM images and corresponding FFT results of the (a,d)as-prepared,(b,e) illuminated, and (c,f) regenerated Ni@NiOx SrTiO3 composite material. The observed changesin morphology and composition of the Ni@NiOx co-catalysts during overall water splitting are also schematicallyindicated.

Mentions: To further support the results obtained by XPS, HRTEMwas used(see Figure 4, as wellas Figures S9 and S10 in the SupportingInformation). The Ni@NiOx particles inas-prepared BSTO1000-NiOx(Figure 4a) clearly show the core–shellstructure (in sizes of ∼8–10 nm, with a metallic Nicore of ∼6 nm), in agreement with previous reports and XPSdata.5 The corresponding d-spacing of the lattice fringes obtained from fast Fourier transformation(FFT) indicate the presence of metallic Ni(111), and NiO(220). Afterillumination, i.e., after the first transients shown in Figure 2, the structure maintains thecore–shell morphology. However, the metallic Ni core appearssmaller than in the fresh sample (Figure 4b), and the shell appears thicker and seemsto be composed of two separate phases. The d-spacingvalues derived from the FFT analysis of a variety of Ni@NiOx particles (Figure 4b, all d-spacings are included in Table S3 in the Supporting Information), includevalues of 6.7–7.7, 2.96, and 2.36 Å, which confirms thepresence of NiOOH.16 The additional d-spacings also indicate the presence of Ni (2.06 Å)and NiO (2.41 Å). Hence, it is reasonable to assume that theshell is composed of NiO with superpositioned NiOOH. The regeneratedsample shows different morphologies (Figure 4c). Besides residual core–shell structures,a Ni(OH)2 phase with small spots of larger contrast embedded in the Ni(OH)2 layer is apparent, which, according to FFT analysis, likely consistof metallic Ni (see Figure S9 in the SupportingInformation).


Transient Behavior of Ni@NiO x Functionalized SrTiO 3 in Overall Water Splitting
HRTEM images and corresponding FFT results of the (a,d)as-prepared,(b,e) illuminated, and (c,f) regenerated Ni@NiOx SrTiO3 composite material. The observed changesin morphology and composition of the Ni@NiOx co-catalysts during overall water splitting are also schematicallyindicated.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384480&req=5

fig4: HRTEM images and corresponding FFT results of the (a,d)as-prepared,(b,e) illuminated, and (c,f) regenerated Ni@NiOx SrTiO3 composite material. The observed changesin morphology and composition of the Ni@NiOx co-catalysts during overall water splitting are also schematicallyindicated.
Mentions: To further support the results obtained by XPS, HRTEMwas used(see Figure 4, as wellas Figures S9 and S10 in the SupportingInformation). The Ni@NiOx particles inas-prepared BSTO1000-NiOx(Figure 4a) clearly show the core–shellstructure (in sizes of ∼8–10 nm, with a metallic Nicore of ∼6 nm), in agreement with previous reports and XPSdata.5 The corresponding d-spacing of the lattice fringes obtained from fast Fourier transformation(FFT) indicate the presence of metallic Ni(111), and NiO(220). Afterillumination, i.e., after the first transients shown in Figure 2, the structure maintains thecore–shell morphology. However, the metallic Ni core appearssmaller than in the fresh sample (Figure 4b), and the shell appears thicker and seemsto be composed of two separate phases. The d-spacingvalues derived from the FFT analysis of a variety of Ni@NiOx particles (Figure 4b, all d-spacings are included in Table S3 in the Supporting Information), includevalues of 6.7–7.7, 2.96, and 2.36 Å, which confirms thepresence of NiOOH.16 The additional d-spacings also indicate the presence of Ni (2.06 Å)and NiO (2.41 Å). Hence, it is reasonable to assume that theshell is composed of NiO with superpositioned NiOOH. The regeneratedsample shows different morphologies (Figure 4c). Besides residual core–shell structures,a Ni(OH)2 phase with small spots of larger contrast embedded in the Ni(OH)2 layer is apparent, which, according to FFT analysis, likely consistof metallic Ni (see Figure S9 in the SupportingInformation).

View Article: PubMed Central - PubMed

ABSTRACT

Transients in thecomposition of Ni@NiOx core–shellco-catalysts deposited on SrTiO3 arediscussed on the basis of state-of-the-art continuous analysis ofphotocatalytic water splitting, and post-XPS and TEM analyses. Theformation of excessive hydrogen (H2:O2 ≫2) in the initial stages of illumination demonstrates oxidation ofNi(OH)2 to NiOOH (nickel oxyhydroxide), with the lattercatalyzing water oxidation. A disproportionation reaction of Ni andNiOOH, yielding Ni(OH)2 with residual embedded Ni, occurswhen illumination is discontinued, which explains repetitive transientsin (excess) hydrogen and oxygen formation when illumination is reinitiated.

No MeSH data available.