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The prepared TCPP/CuNiCo2O4 noble metal-free nanocatalysts improved the catalytic performance of methanol oxidation reaction under light.

Z-scheme photocatalytic system has been regarded as a popular field of research in photoelectrochemical (PEC) water splitting. Among the many obstacles facing a Z-scheme photocatalytic system, the analysis methods of interfacial Z-scheme charge transfer still remain a significant challenge. Hence, in this study, CdS/Ti-Fe2O3 heterojunction photoanodes are elaborately designed to explore the charge-transfer behavior in PEC water splitting. In this study, photophysical measurements, including the Kelvin probe measurement, surface photovoltage spectroscopy (SPV), and transient photovoltage spectroscopy (TPV), are used to monitor the migration behavior of photogenerated charges at the interface electric field of CdS/Ti-Fe2O3 Z-scheme heterojunction photoanodes. The Kelvin probe and SPV measurements demonstrate that CdS/Ti-Fe2O3 interfacial driving force favors the rapid transfer of photoexcited electrons to CdS. The double-beam strategy based on TPV indicates that more electrons of Ti-Fe2O3 are combined with the holes of CdS owing to the intensive interface electric field. The results of these measurements successfully prove the Z-scheme migration mechanism of CdS/Ti-Fe2O3 photoanodes. Benefiting from the desirable charge transfer at the interface electric field, CdS/Ti-Fe2O3 photoanodes exhibit superior photocatalytic oxygen evolution reaction performance compared with that of pure Ti-Fe2O3. The photocurrent density of the 25CdS/Ti-Fe2O3 photoanode reaches 1.94 mA/cm2 at 1.23 V versus reversible hydrogen electrode without excess cocatalyst, and it is two times higher than that of pure Ti-Fe2O3 photoanode. Therefore, an outstanding strategy is provided in this study to prove the Z-scheme charge-transfer mechanism of photocatalytic systems in PEC water splitting.

Designing durable, high-active, and low-cost noble-metal-free photoelectrocatalysts for methanol electrooxidation is highly demanded but remains a challenge. Herein, the photoelectrocatalytic activity of cobalt-copper layer double hydroxide (CoCu-LDH) for methanol oxidation reaction (MOR) in the alkaline media under light was remarkably enhanced by cerium (Ce) doping and further by 5,10,15,20-tetrakis(4-carboxylphenyl)porphyrin (TCPP) modification. TCPP/Ce-CoCu-LDH exhibits a remarkable mass activity of 1788.2 mA mg

Coupling porphyrins with semiconductors is demonstrated as one of effective means to facilitate the separation of photogenerated charge in dye-sensitized solar cells as well as photocatalytic hydrogen production. However, there are limited reports about exploring the effect of porphyrin on the behavior of photogenerated charges and photoelectrochemical (PEC) water oxidation performance. Herein, we have built a hybrid photoanode containing Ti doped α-Fe

Inevitable drawbacks on α-Fe2O3 photoanodes, such as poor conductivity, short hole diffusion length, high electron-hole recombination rate, limit their photoelectrochemical (PEC) performance for water oxidation. The construction of heterojunction is an effective approach to improve the PEC performance of photoanodes. Herein, we report the design of the WO3/Ti–Fe2O3 heterojunction photoanodes, which are synthesized by two simple hydrothermal method. The optimized WO3/Ti–Fe2O3 photoanode shows remarkably improved photocurrent of 2.15 mA/cm2 at 1.23 V versus reversible hydrogen electrode (RHE) without additional cocatalyst, which is higher than that of previous literatures. The improvement benefits from reduced charge transfer resistance in the bulk of Ti–Fe2O3 photoanode and improved charge separation efficiency, which can been further confirmed by electrochemical impedance spectroscopy (EIS), the transient photovoltage (TPV) and the work function (WF) measurement. The present work also provide new opportunities in developing high performance photoanodes for PEC water splitting.

Solar-driven production of renewable energy (e.g., H2) has been investigated for decades. To date, the applications are limited by low efficiency due to rapid charge recombination (both radiative and nonradiative modes) and slow reaction rates. Tremendous efforts have been focused on reducing the radiative recombination and enhancing the interfacial charge transfer by engineering the geometric and electronic structure of the photocatalysts. However, fine-tuning of nonradiative recombination processes and optimization of target reaction paths still lack effective control. Here we show that minimizing the nonradiative relaxation and the adsorption energy of photogenerated surface-adsorbed hydrogen atoms are essential to achieve a longer lifetime of the charge carriers and a faster reaction rate, respectively. Such control results in a 16-fold enhancement in photocatalytic H2 evolution and a 15-fold increase in photocurrent of the crystalline g-C3N4 compared to that of the amorphous g-C3N4.

A high-efficient oxygen evolution cocatalyst decorated on α-Fe2O3 has been considered as one of the most prospective approaches to accelerate the charge transport at the interface between photoanod...

Acid-treatment has been proved to be an efficient approach to improve the photoelectrochemical (PEC) performance of hematite. However, efforts to optimize hematite photoanode have been limited by an inadequate understanding of the semiconductor surface. Here we make efforts to understand the microscopic charge separation processes of Ti4+ doped Fe2O3 photoanode before and after acid-treatment. Surface photovoltage (SPV) transient and the work function measurements directly reveal that acid-treatment leads to passivation of the surface states. Surface photovoltage (SPV) spectroscopic studies coupled to open-circuit photovoltage (OPV) measurements indicate that the surface states of hematite photoanode before acid-treatment result in the pinning of the Fermi level, which reduce the intensity of interfacial electric field at the semiconductor-electrolyte interface.

Modifying inexpensive cocatalysts on semiconductors to accelerate the charge transfer at the photoanode/electrolyte interface, which possess good charge transfer in the bulk photoanode simultaneously, is priority among priorities in constructing low-cost and efficient PEC solar energy conversion devices. However, it is often difficult to satisfy outstanding charge transfer both in the bulk and at the photoanode/electrolyte interface when integrating cocatalysts with semiconductors. In our work, we synthesized FeP-decorated Ti–Fe2O3in situ through simple low-temperature phosphidation, which possessed good interfacial contact between Ti–Fe2O3 and FeP. The results demonstrated that the in situ deposition of FeP not only reduced the charge transfer resistance in the bulk photoanode by improving the electrical conductivity, but also accelerated the charge transfer at the photoanode/electrolyte interface. Based on the above advantages, the novel FeP/Ti–Fe2O3 exhibited splendid photocurrent density as high as 3.9 mA cm−2 at 1.23 V vs. RHE; meanwhile, the onset potential of FeP/Ti–Fe2O3 shifted cathodically to 0.88 V vs. RHE in comparison with that of Ti–Fe2O3 (0.98 V vs. RHE). This work paves a simple path to construct a cocatalyst-modified photoanode with excellent interfacial charge transfer and offers a low-cost and promising cocatalyst that can be applied in the photoelectrochemical water oxidation reaction.

Semiconductor electrodes integrated with cocatalysts are key components of photoelectrochemistry (PEC)-based solar-energy conversion. However, efforts to optimize the PEC device have been limited by an inadequate understanding of the interface interactions between the semiconductor-cocatalyst (sem|cat) and cocatalyst-electrolyte (cat|ele) interface. In our work, we used ferrihydrite (Fh)-modified Ti-Fe2 O3 as a model to explore the transfer process of photogenerated charge carriers between the Ti-Fe2 O3 -Fh (Ti-Fe2 O3 |Fh) interface and Fh-electrolyte (Fh|ele) interface. The results demonstrate that the biphasic structure (Fh/Ti-Fe2 O3 ) possesses the advantage that the minority hole transfer from Ti-Fe2 O3 to Fh is driven by the interfacial electric field at the Ti-Fe2 O3 |Fh interface; meanwhile, the holes reached at the surface of Fh can rapidly inject into the electrolyte across the Fh|ele interface. As a benefit from the improved charge transfer at the Ti-Fe2 O3 |Fh and Fh|ele interface, the photocurrent density obtained by Fh/Ti-Fe2 O3 can reach 2.32 mA cm-2 at 1.23 V versus RHE, which is three times higher than that of Ti-Fe2 O3 .

In this report, a hierarchical porous carbon microtubes (CMTs) coated by carbon skeleton was prepared simply and the better role of carbon skeleton in increasing the capacity of CMTs was also investigated. SEM, XRD and XPS were used to character the morphology, crystal structure and the functional group of CMTs and CMTs-coated carbon skeleton. Electrochemistry of materials was conducted by CV and constant-current techniques. The results show that the carbon skeleton improves the electric conductivity of materials and thus a better stability of capacity during charge and discharge was obtained (from 81.2 to 97.1% of original specific capacitance after 10000 GCD cycles at 1 A g−1), although the high specific surface area were altered weakly (1159 m2 g−1). Besides, the incorporated nitrogen-containing functional group can increase the gravimetric capacitance of materials from 253 F g−1 to 278 F g−1, with the volumetric capacitance up to 152 F cm−3. The adequate utilization of nature characteristic of biomass and the simple synthesis of stable carbon skeleton offers a good alternative route for advance CMTs.

Although Z-scheme effect plays a significant role in explaining the transfer mechanism of photogenerated electrons and holes between semiconductor heterostructure, the existence of Z-scheme effect can only be proved via limited photocatalytic experimental means as an indirect evidence at present. Our research confirms the direct evidence of Z-scheme effect according to the experimental results from the view of thermodynamics and kinetics, and substantiates the typical competitive relation for transfer of photogenerated electrons and holes between Z-scheme effect and traditional semiconductor heterostructure effect respectively. The surface photovoltage (SPV) spectroscopy, photoacoustic (PA) spectroscopy and transient photovoltage (TPV) are firstly applied in the study of Z-scheme effect between titanium oxide and cadmium sulfide (TiO2/CdS) heterostructure. SPV and PA responses are generally acknowledged as classic technologies to analyze the excitation, separation, transfer and recombination properties on photogenerated electrons and holes, and TPV responses are an indispensable method to study the behavior of photogenerated electrons and holes.

Nickel phosphide (Ni2P) was used as an excellent water oxidation cocatalyst for photoelectrochemical (PEC) water splitting, which could significantly promote the hole injection efficiency and suppress the back reaction of water oxidation over a Ti4+ doped Fe2O3 photoanode.

In this work, an anthracene-based MOF, Zr–ADBEB, was prepared by coordination reaction of zirconium chloride and 4,4′-anthracene-9,10-diylbis(ethyne-2,1-diyl) dibenzoic acid (ADBEB). After the loading of different amount of Pt nanoparticles by post chemical reduction of hexachloroplatinic acid with sodium borohydride, the MOF presented greatly improved activity towards visible light hydrogen (H2) evolution. It was identified that band bending of the MOF is downward towards surface, which is effective to promote separation of the photogenerated charge carriers and transportation of the photogenerated electrons from the MOF to the Pt cocatalyst to contribute to the H2 evolution. The Zr–ADBEB MOF photocatalyst decorated by optimal amount of Pt cocatalyst, i.e., 1.0 wt%, exhibited a H2 evolution rate as high as 704 μmol·h−1·g−1, ca. 220 times of that of pristine Zr–ADBEB MOF (3.2 μmol·h−1·g−1).

Nickel, a non-noble metal, is one of the most promising candidates for photocatalysis because it is inexpensive and an earth-abundant metal. Herein, Ni/CM-C3N4 nanocomposites with Ni as a cocatalyst were synthesized by a simple solvothermal method. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed that Ni nanoparticles were loaded onto the surface of CM-C3N4. The prepared Ni/CM-C3N4 nanocomposites exhibited an enhanced hydrogen evolution activity. The most active catalyst contained 10% Ni and produced H2 at a rate of 313.2 μmol h−1 g−1, which was obviously higher than that of pure CM-C3N4. The results of photoluminescence (PL) and photoacoustics (PA) studies indicated that the recombination efficiency of photo-induced electron–hole pairs was decreased for CM-Ni10 as compared to that for unmodified CM-C3N4. The transient photovoltage (TPV) measurements directly demonstrated that the recombination time of electron–hole pairs in CM-Ni10 was prolonged. More importantly, the reversed surface photovoltage (SPV) and the declined surface photocurrent (SPC) response of CM-Ni10 revealed that the photogenerated electrons could be trapped by Ni, leading to a better separation efficiency and a superior hydrogen production. Finally, the possible mechanism is proposed to illuminate the photogenerated charge behavior between CM-C3N4 and Ni, which might provide a theoretical basis to develop efficient cocatalysts for photocatalytic water splitting.

Cocatalyst nickel sulfide (Ni3S2) was successfully loaded onto TiO2 nanotube array (TiO2 NTA) photoanodes for the first time by a simple two step hydrothermal process. The prepared Ni3S2/TiO2 NTA photoanode shows better photoelectrochemical (PEC) water splitting activity compared to pure TiO2 NTAs. The surface photovoltage (SPV) spectroscopy and transient photocurrent measurements provide direct evidence for the efficient charge separation of the Ni3S2/TiO2 NTA photoanode. Furthermore, the work function measurement proved the formation of the interfacial electric field at the interface of Ni3S2 and TiO2, which is the main driving force of charge separation. Photoelectrochemical impedance spectroscopy (PEIS) measurements and oxygen evolution reaction (OER) polarization curves confirmed that the Ni3S2/TiO2 NTA photoanode effectively reduces the interfacial charge transfer resistance and suppresses the overpotential of water oxidation, which make the photogenerated holes take part in the water oxidation reaction easily. These results demonstrate that Ni3S2 could be an excellent cocatalyst when applied in PEC water oxidation.

Nickel phosphide (Ni