Hierarchically Assembling CoFe Prussian Blue Analogue Nanocubes on CoP Nanosheets as Highly Efficient Electrocatalysts for Overall Water Splitting

Abstract

At present, to boost the sluggish kinetic of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), precious Pt and Ir/Ru-based electrocatalysts are usually employed and acknowledged as benchmark in practical application. [3,4] However, their high cost has been considered as an insurmountable barrier. [5] Therefore, numerous efforts have been undertaken to exploit alternative electrocatalysts with cost-effective and high efficiency. [6][7][8] Moreover, bifunctional electrocatalysts are especially important from the technological point of view owing to their facility for cell assembly and reduced manufacture cost accordingly. [9] Among the booming earth-abundant alternatives, including transition metalbased oxide, [10] nitrides, [11] phosphides, [12] and selenides, [13] transition metal phosphides (TMPs) have sparked considerable attention due to their metalloid characteristics and superior electrical conductivity, thus demonstrated as promising bifunctional electrocatalysts. [14] Various approaches have been proposed to enhance the electrocatalytic performance of TMPs from the aspects of incorporation of foreign metal sites or surface coating, for example the preparation of bimetallic phosphide, [15] Cu 3 P coated by a N,Pcodoped carbon shell, [16] and CoP/TiO x heterostructure, [17] etc. Moreover, rational design of a catalyst with favorable electronic and geometric structure is also of prerequisite towards the rapid electron transfer and mass transport. [18] From this perspective, 2D TMPs nanosheets can serve as one of the most prospective candidates owing to their high surface area-to-volume ratio, highly exposed active sites, large contact area with electrolyte. Benefitted from the reduced thickness of TMPs nanosheets, the low-coordinated sites on the catalysts' surface including steps, edges, and kinks will be favorable for electrocatalytic process. [19,20] Nevertheless, due to the shrinkage and fusion caused by stress and decomposition, nanosheets are prone to collapse and thus the impaired electrocatalytic activities limit their application. In this regard, rational design of hierarchical heterostructures based on 2D TMPs nanosheets is highly desirable.Prussian blue (PB) and PB analogues (PBA) formed by coordination interaction between cyanide ligands and metal ions Efficient and durable electrocatalysts are highly desirable for overall water splitting. Herein, a facile strategy is demonstrated to rationally construct CoFe Prussian blue analogues (PBA)@CoP cube-on-sheet hierarchical structure by etching reaction with intermediated CoO to form PBA nanocubes. Benefitting from the heterostructured engineering, the as-synthesized CoFe PBA@CoP presents remarkable electrocatalytic performance in 1.0 m KOH, only requiring overpotentials of 100 mV for hydrogen evolution reaction (HER) and 171 mV for oxygen evolution reaction (OER) to reach the 10 mA cm −2 current density with good stability. Extraordinarily enhanced electrocatalytic performance is ascribed to not only the rapid charge transfer ...

Multifunctional Ultrathin Amorphous CoFe-Prussian Blue Analogue Catalysts for Efficiently Boosting the Oxygen Evolution Activity of Antimony-Doped TiO2 Nanorods Photoanode

“…11,26,27 The Co 2p spectrum shows two intense peaks at 782 and 797.8 eV, which can be assigned to the spin-orbit doublets of Co 2p 3/2 and Co 2p 1/2 , respectively. The result confirms the +3 oxidation state of Co. 23,28 The Fe 2p core-level spectrum in Figure 2d shows a prominent peak centered at 710.6 eV and a weak peak at 721 eV, assigned to the Fe 2p 3/2 and Fe 2p 1/2 , respectively, indicating the +3 oxidation state of Fe in KCo[Fe(CN) 6 ]. 28−30 The light-harvesting efficiency (Figure 3a) of the photoanodes is calculated as LHE% = 1 − 10 −A(λ) , where A(λ) is the absorbance at different wavelengths obtained from the UV−vis 21,22 The extended visible light-harvesting efficiency of the CoFe-PBA(8)/Sb-TiO 2 photoanode is attributed to the presence of cyanide groups (−CN) in the CoFe-PBA catalyst.…”

Phase‐Controlled Synthesis of Nickel‐Iron Nitride Nanocrystals Armored with Amorphous N‐Doped Carbon Nanoparticles Nanocubes for Enhanced Overall Water Splitting

“…Compared with that of NiFe-PBAs, no featured FT-IR vibration peaks centered at ≈2100 cm -1 are observed for NiFe-PBAs-250 and NiFe-PBAs-350 samples, indicating the loss of CN group in them. [32] Moreover, the latter two samples show nearly identical FT-IR spectra, implying that there is hardly change in microstructure when the annealing temperature exceeds 250 °C and most of CNligands have been removed at 250 °C. Subsequently, the obtained NiFe-PBAs nanocubes are transformed into NiFe oxides/NC NPNCs by means of annealing treatment in air at 350 °C for 2 h, whose component is confirmed by XRD pattern and X-ray photoelectron spectra (XPS), shown in Figure S5 2) The generated NC component or shell layer exists in amorphous form that is hard to be graphitized due to the relatively low nitridation temperature, as evidenced by Raman spectrum analyses (Figure S9, Supporting Information) and subsequent microstructural characterization.…”

“…And the Raman spectrum analysis (Figure S1B, Supporting Information) shows two featured peaks centered at 2066 and 2187 cm -1 , proving the existence of CN or cyano functional group in NiFe-PBAs. [32] As revealed by field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) analyses (Figure S2, Supporting Information), the obtained NiFe-PBAs are highly uniform nanocubes with smooth surfaces, whose average edge length is measured to be about 150-180 nm. Further thermogravimetric analysis (TGA) of NiFe-PBAs under air (Figure S3, Supporting Information) displays two obvious weight loss processes at room temperature to 250 and 250-350 °C, respectively.…”

Paired Electrolysis of Acrylonitrile and 5-Hydroxymethylfurfural for Simultaneous Generation of Adiponitrile and 2,5-Furandicarboxylic Acid

“…The peaks at 229.6 and 233.1 eV are associated with Mo 4+ [37] originated from the reduction of MoO 4 −2 during the electrodeposition process. For P 2p spectra (Figure 3c), the peak at 133.1 eV is characteristic of phosphate species due to superficial oxidation of the NiMoP after exposure to air [38]. The intensity of peaks in the Mo 3d and P 2p region drastically drops after electrolysis, suggesting that the Mo and P elements are selectively removed by being oxidized into water-soluble anions.…”