Hematite is a promising photoanode material for renewable solar fuel production via photoelectrochemical (PEC) water splitting. However, the fast electron−hole recombination and sluggish surface reaction retard it from getting satisfied performance. Herein, hematite nanorod arrays doped with titanium (Ti−Fe 2 O 3 ) on the surface were prepared by a solutionbased process. Because of one-dimension anisotropy and improved charge transfer property, the photocurrent density is doubled compared to pure Fe 2 O 3 at 1.50 V vs RHE under simulated sunlight (AM 1.5 G) irradiation. Loading conjugated Ni(OH) 2 /IrO 2 cocatalyst further leads to about 200 mV negative shift of the onset potential and dramatic increase of the applied bias photon-to-current efficiency (ABPE). We find that Ni(OH) 2 can efficiently capture the photogenerated holes from hematite as a hole-storage layer (HSL) to improve the charge transfer process across the interface of hematite and IrO 2 electrocatalyst. Furthermore, the stored photogenerated holes in Ni(OH) 2 can be utilized by IrO 2 for water oxidation more facilely. This synergetic effect along with the efficient surface doping are proposed to be responsible for the enhanced performance.
Artificialp hotosynthesis requires the practical use of efficient, robust, and economical water-oxidation catalysts (WOCs) for chemical-fuel production. The synthesis of amorphous cobalt oxide nanoparticles (ca. 2nm) is reported as aW OC with a turnoverf requency up to 8.6 s À1 in the photocatalytic Ru(bpy) 3 2 + -Na 2 S 2 O 8 system (bpy = 2,2'-bipyridyl). This activity is unprecedented in heterogeneousc obalt-based WOCs and is even comparable to that of as tate-of-the-art homogeneous cobalt-based polyoxometalate catalyst. With the help of experimental and computational X-ray absorption spectroscopy,t he atomic structure of the synthesized amorphous cobalt oxide nanoparticles was characterized, and it consists of ao ne-dimensional chain of dimeric edge-sharing CoO 6 octahedra.T heoreticalc alculations suggest that this structure was able to promote OÀOb ond coupling, unlike crystalline cobalt oxide WOCs, which led to the enhanced water-oxidation activity.Artificialp hotosynthesis, which converts solar energy into chemicalf uels, is ap romisingw ay to solveo ur energy ande nvironmental challenges. [1] However,t his whole process commonly suffers from as ignificant loss in conversion efficiency; this is partially duet ot he sluggish kinetics of water oxidation, which involves af our-proton-coupled electron-transfer trans-formation. [2] To alleviate this problem, various water-oxidation catalysts (WOCs) have been developedt oa ccelerate the wateroxidation reaction thus to improve the overall efficiency of solar-energy conversion. [3] Among the developed WOCs, iridium and ruthenium oxides fulfill the efficiency and stability requirements, but the rareness of these elements prohibit their large-scale use. [4] Intense efforts are currently being directed towardst he searchf or efficient, robust, and earth-abundant WOCs with the ultimate aim to obtain practical artificial photosynthetic systems.Av ariety of cobalt-based homogeneous WOCs have been demonstrated to be promising candidates. [5] For example, complexes such as (TPA)Co-(m-OH)(m-O 2 )Co(TPA)(ClO 4 ) 3 (TPA = tris(2pyridylmethyl)amine) and Co 4 O 4 (py) 4 (OAc) 4 (py = pyridine, OAc = acetate) were reported as active WOCs. [6] Homogeneous WOCs often exhibit highera ctivity than their heterogeneous counterparts and enable accurate structural determination and ad etailed kinetic study. [7] However,h omogenous WOCs usually face challenges in terms of stabilitya nd synthetic costs. [8] A breakthrough in the development of homogenous WOCs was the discovery of ac obalt-based carbon-free polyoxometalate reported by Hill et al. [9] This catalystw as shown to possess both high activity and good stability.Cobalt-based heterogeneous WOCs such as oxides and hydroxides are also interesting, because they are usually more robust and cheaper than homogeneousW OCs and are thus conducive to practical large-scale applications. [10] As eries of cobalt-based oxide nanostructures such as Co 3 O 4 particless upported by mesoporouss ilica, Co(OH) 2 anchored on zeolite,a nd LaCoO 3 na...
Deposition of cocatalyst is an efficient way for photocatalytic water splitting to improve solar energy conversion efficiency, and its deposition method has been known to make a great effect. In this work, we introduced a sulfurization-assisted deposition method to load earth-abundant cobalt cocatalyst for the purpose of promoting water oxidation performance of Sm 2 Ti 2 S 2 O 5 oxysulfide that is characterized with wide visible light absorption. The cobalt deposition introduced here undergoes first formation of CoS x by sulfurization at high temperature and subsequent conversion into CoO x by calcinations in air. Compared to conventionally impregnated cobalt or IrO 2 colloids, the sulfurization-assisted cobalt deposition well maintains structure of photocatalyst and inhibits the formation of defect sites leading to better separation of photogenerated carriers and water oxidation performance. The apparent quantum efficiency of the optimized sample reaches 5.0% at 420 nm. The sulfurization-assisted deposition actually open a new way to modify the (oxy)sulfide semiconductors.
Mg2+ doped nanoscale Cu–Mg/ZnO catalysts prepared by the co-precipitation method have been systematically characterized focusing on the amount of Mg2+ ions incorporated.
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