Hematite Photoanode with Complex Nanoarchitecture Providing Tunable Gradient Doping and Low Onset Potential for Photoelectrochemical Water Splitting

Abstract

Over the past years, α-Fe O (hematite) has re-emerged as a promising photoanode material in photoelectrochemical (PEC) water splitting. In spite of considerable success in obtaining relatively high solar conversion efficiency, the main drawbacks hindering practical application of hematite are its intrinsically hampered charge transport and sluggish oxygen evolution reaction (OER) kinetics on the photoelectrode surface. In the present work, we report a strategy that synergistically addresses both of these critical limitations. Our approach is based on three key features that are applied simultaneously: i) a careful nanostructuring of the hematite photoanode in the form of nanorods, ii) doping of hematite by Sn ions using a controlled gradient, and iii) surface decoration of hematite by a new class of layered double hydroxide (LDH) OER co-catalysts based on Zn-Co LDH. All three interconnected forms of functionalization result in an extraordinary cathodic shift of the photocurrent onset potential by more than 300 mV and a PEC performance that reaches a photocurrent density of 2.00 mA cm at 1.50 V vs. the reversible hydrogen electrode.

Activation of α‐Fe2O3 for Photoelectrochemical Water Splitting Strongly Enhanced by Low Temperature Annealing in Low Oxygen Containing Ambient

“…The Zn‐Co LDH was produced by a simple microwave synthesis. For decoration Fe‐oxide layers were immersed in a solution in which Zn‐CO LDH was dispersed for 10 min as described elsewhere . The results of PEC water splitting measurements for decorated samples and layer characterization are shown in Figure S6.…”

“…For decoration Feoxide layers were immersed in as olution in which Zn-CO LDH was dispersed for 10 min as described elsewhere. [20] The results of PEC water splitting measurements for decorated samples and layer characterization are shown in Figure S6. The surface SEM image exhibits that the morphology is similar to LO sample before treatment (Figure 1(c)), and no precipitate due to the Zn-Co LDH treatment is found.…”

“…In order to enhance the PEC performanceo fa-Fe 2 O 3 ,awide range of approaches have been explored,s uch as nanostructuring, [14] elemental doping (e.g.,b yS n, Ti,S i), [15][16][17] and decoration by various oxygen evolution reaction (OER) co-catalysts (e.g.,I rO 2 ,C o-Pi (Co-phosphate), Zn-Co layered double hydroxides (LDH)). [18][19][20] Nanostructuring of a-Fe 2 O 3 provides ah ighly improved efficiency in chargec arrier generation and collection due to the enhancement of the specific surface area and the drastic shortening of the minority carrierd iffusion length. [14] Nanostructured a-Fe 2 O 3 has been synthesized using av ariety of techniques including sol-gel processing, [21] electrodeposition, [22] spray pyrolysis, [23] hydrothermal synthesis, [20,24] magnetron sputtering, [25,26] and electrochemical anodization.…”

“…[18][19][20] Nanostructuring of a-Fe 2 O 3 provides ah ighly improved efficiency in chargec arrier generation and collection due to the enhancement of the specific surface area and the drastic shortening of the minority carrierd iffusion length. [14] Nanostructured a-Fe 2 O 3 has been synthesized using av ariety of techniques including sol-gel processing, [21] electrodeposition, [22] spray pyrolysis, [23] hydrothermal synthesis, [20,24] magnetron sputtering, [25,26] and electrochemical anodization. [27,28] Among them, anodization is considered as ap romising methodf or the fabrication of nanostructured a-Fe 2 O 3 from the viewpoint of low cost and large scale production.…”

Ultrathin Hematite Photoanode with Gradient Ti Doping

“…For example, Abdi and coworkers developed gradient W-doped BiVO 4 photoanodes via the layer-by-layer spray pyrolysis method, consisting of 10-step different gradient W concentration, which ultimately facilitated the efficiency of photogenerated carriers because of the built-in electric field [23]. However, the strategy of such tactfully introducing gradient in doping profile has been rarely conducted for hematite-based photoanodes, and it mainly focuses on surface-doped hematite with nonmetallic element P, which might not be the ideal choice for hematite photoelectrode [24,26]. Moreover, the surface doping only functionalizes near the semiconductor/liquid interface andcannot facilitate the charge transfer in the bulk, which significantly limits the overall PEC water splitting performance [18].…”