Search

Photoelectrochemical (PEC) water splitting that functions in pH-neutral electrolyte attracts increasing attention to energy demand sustainability. Here, we propose a strategy to in situ form a NiB layer by tuning the composition of the neutral electrolyte with the additions of nickel and borate species, which improves the PEC performance of the BiVO 4 photoanode. The NiB/BiVO 4 exhibits a photocurrent density of 6.0 mA cm −2 at 1.23 V RHE with an onset potential of 0.2 V RHE under 1 sun illumination. The photoanode displays a photostability of over 600 hours in a neutral electrolyte. The additive of Ni 2+ in the electrolyte, which efficiently inhibits the dissolution of NiB, can accelerate the photogenerated charge transfer and enhance the water oxidation kinetics. The borate species with B─O bonds act as a promoter of catalyst activity by accelerating proton-coupled electron transfer. The synergy effect of both species suppresses the surface charge recombination and inhibits the photocorrosion of BiVO 4 .

In photoelectrochemical water splitting, little attention is paid to the volume change of the cocatalyst on photoelectrodes during long-term testing, which is one of the important reasons for the decay of stability of photocorroded electrodes. Tuning the electrolyte composition (e.g. Fe2+ additives) has been demonstrated to be an efficient approach for in situ cocatalyst regeneration and photocorrosion inhibition. Photoelectrode stabilization by surface passivation is adopted as the most vital approach for obtaining high stability. Herein, we challenge the traditional strategy to in situ passivate the surface states with a “surface-protected etching” process for tuning the electrolyte composition via employing F− anions in borate buffer. The F− species could incorporate into the Co-catalyst to activate catalytic sites for cocatalyst reconstruction, improving the charge transport of BiVO4. More importantly, the dynamic migration of F− anions with strong chemical bonds suppresses the volume change of the cocatalyst, passivates the surface states of BiVO4/cocatalyst, and minimizes the dissolution of BiVO4 over long-term measurement, which further inhibits the photocorrosion of electrodes. The resulting photoanode allows stable oxygen evolution over 100 h at a low potential of 0.6 VRHE, which is superior to the traditional NiOOH/FeOOH double layer cocatalyst. This finding on in situ etching and passivation engineering shines a light on boosting the stability of photoelectrodes in such electrolyte systems.

Improving charge transport and reducing bulk/surface recombination can increase the activity and stability of BiVO4 for water oxidation. Herein we demonstrate that the photoelectrochemical (PEC) performance of BiVO4 can be significantly improved by potentiostatic photopolarization. The resulting cocatalyst-free BiVO4 photoanode exhibited a record-high photocurrent of 4.60 mA cm-2 at 1.23 VRHE with an outstanding onset potential of 0.23 VRHE in borate buffer without a sacrificial agent under AM 1.5G illumination. The most striking characteristic was a strong "self-healing" property of the photoanode, with photostability observed over 100 h under intermittent testing. The synergistic effects of the generated oxygen vacancies and the passivated surface states at the semiconductor-electrolyte interface as a result of potentiostatic photopolarization reduced the substantial carrier recombination and enhanced the water oxidation kinetics, further inhibiting photocorrosion.

In situ catalyst regeneration of NiFe-based oxygen evolution catalyst (OEC) has been recognized as one of the best approaches for photocorrosion inhibition on water splitting photoelectrodes. Howev...

Increasing long-term photostability of BiVO4 photoelectrode is an important issue for solar water splitting. The NiOOH oxygen evolution catalyst (OEC) has fast water oxidation kinetics compared to the FeOOH OEC. However, it generally shows a lower photoresponse and poor stability because of the more substantial interface recombination at the NiOOH/BiVO4 junction. Herein, we utilize a plasma etching approach to reduce both interface/surface recombination at NiOOH/BiVO4 and NiOOH/electrolyte junctions. Further, adding Fe2+ into the borate buffer electrolyte alleviates the active but unstable character of etched-NiOOH/BiVO4 , leading to an outstanding oxygen evolution over 200 h. The improved charge transfer and photostability can be attributed to the active defects and a mixture of NiOOH/NiO/Ni in OEC induced by plasma etching. Metallic Ni acts as the ion source for the in situ generation of the NiFe OEC over long-term durability.

In photoelectrochemical (PEC) water splitting, exploring highly active cocatalysts, especially Mn-based catalysts, is becoming more important in enabling a comparison of a number of Co-, Fe-, and Ni-based traditional cocatalysts in solar water oxidation. Herein, we for the first time synthesized an efficient Mn-based (oxy)hydroxide catalyst through MnSe as an intermetallic phase. As iron was further incorporated into the MnSe, the MnFeSe electrode showed an outstanding oxygen evolution reaction (OER) activity (an overpotential of 247 mV at 10 mA cm−2) and reaction kinetics (a Tafel slope of 35 mV dec−1). The MnFeSe was electrochemically converted to Se-incorporated MnFe (oxy)hydroxides under oxidative potential during the OER. Remarkably, the novel Mn-based multi-metal catalyst was applied to BiVO4 for solar-driven water splitting. The resulting photoelectrode exhibited a current density of 4.85 mA cm−2 at 1.23 VRHE in 1 M KBi under AM 1.5G illumination. More importantly, a 20 h durability was achieved owing to avoiding the photocorrosion of BiVO4, which is so far the best PEC performance using a highly active Mn-based cocatalyst compared to the common MnOx. Further DFT calculations on models of MnSe, MnFeSe, MnOOH, Se,Fe–MnOOH, MnO2, and Se,Fe–MnO2 explained well the OER/PEC experimental results. This work developed a new strategy for designing and exploring advanced cocatalysts for a practical solar-driven water splitting system.

A photocharge/discharge strategy is proposed to initiate the WO3 photoelectrode and suppress the main charge recombination, which remarkably improves the photoelectrochemical (PEC) performance. The photocharged WO3 surrounded by a 8-10 nm overlayer and oxygen vacancies could be operated more than 25 cycles with 50 h durability without significant decay on PEC activity. A photocharged WO3 /CuO photoanode exhibits an outstanding photocurrent of 3.2 mA cm-2 at 1.23 VRHE with a low onset potential of 0.6 VRHE , which is one of the best performances of p-n heterojunction structure. Using nonadiabatic molecular dynamics combined with time-domain DFT, we clarify the prolonged charge carrier lifetime of photocharged WO3 , as well as how electronic systems of photocharged WO3 /CuO semiconductors enable the effective photoinduced electrons transfer from WO3 into CuO. This work provides a feasible route to address excessive defects existed in photoelectrodes without causing extra recombination.

Solar hydrogen production from seawater, the most natural resource on the earth, is an economically appealing for renewable energy conversion. A photoelectrochemical (PEC) seawater-splitting system is greatly challenging for designing stable photoelectrodes and obtaining high and stable photocurrents, strongly preventing corrosion of semiconductors in seawater. In this context, we for the first time report an ultra-stable seawater splitting PEC cell based on the BiVO4 protected by a MoO3 barrier layer. The combination of MoO3 and Mo/B co-doping on BiVO4 photoanode presents a resembled photocurrent density value of 4.30 mA cm−2 at 1.23 VRHE in simulated seawater and natural seawater under 1 sun AM 1.5 G illumination. Equally importantly, the resulting photoanode is quite stable during natural seawater splitting, which shows strong photocorrosion resistance over 70 hours of continuous irradiation. Further theoretical calculations provide an insight into the roles of surface dopants for the reduction of substantial surface charge recombination and improving the photocorrosion resistance during long-term operation in the marine environment. This work provides a new avenue for the robust and stable PEC semiconductors design for hydrogen production by seawater photoelectrolysis. Broader context Seawater photoelectrolysis is one of the promising alternatives for hydrogen production since sun and seawater represent the two most abundant and available resources reserved on earth. However, the corrosion resistance on photoelectrodes should be paid more attention to long-term operation, where the chloride ions from seawater corrode the electrodes. The highly robust and efficient photoelectrodes are thereby required as for one of the critical points on potential application. The BiVO4 photoelectrode is a promising semiconductor for photoelectrochemical (PEC) seawater splitting with a suitable bandgap and favorable conduction band edge position. Unfortunately, this photoelectrode undergoes a poor charge carrier and serious photocorrosion which restricts practical applications for solar energy conversion. In this context, we develop a robust BiVO4 protected with a MoO3 barrier layer, constructing with surface dual-doping engineering, which serves as an outstanding PEC electrode for natural seawater photoelectrolysis. We further demonstrate that the optimized photoelectrode presents a resembled photocurrent density value in simulated seawater and natural seawater under 1 sun AM 1.5 G illumination, which shows a strong photocorrosion resistance over 70 hours of continuous irradiation, representing one of the targets directly avoiding chloride corrosion on seawater photoelectrolysis.

Increasing long-term photostability of BiVO

The stabilization of semiconductor against photocorrosion has become one of the most essential targets in photoelectrochemical water splitting. Herein, a research of three mixing enhancement strategies of WO3/BiVO4 heterojunction, W doping, and oxygen vacancy formation can be made to incorporate into such a nanostructure during the preparation of BiVO4 in terms of PEC performance improvement. The WO3 layer not only facilitated the electron transfer, but importantly, was used as a diffusion source for W doping which brought oxygen vacancies on the bulk material. Moreover, the introduction of different W doping profiles,- bottom, middle, and top, all electrodes exhibited a photo-activation character with the improved photocurrent and the negative shift of onset potential. The bottom W doping led to the most notable enhancement in charge separation efficiency on BiVO4 electrode, which yielded the close photocurrent densities of ∼4.4 mA cm−2 at 1.23 VRHE under front and back 1 sun illumination. More importantly, the cocatalyst-free W:BiVO4-Ov photoanode present a favorable stability during 25 h test applied at 1.0 VRHE. By experimental and theoretical arguments, it demonstrated that the multiple collaborative strategies shed light on designing efficient and stable photoelectrodes for solar energy conversion.

Stability is one of essential factors for evaluating the photoelectrochemical (PEC) water splitting performance on photocorroded semiconductors for practical applications. Cocatalyst decoration can only maintain the stability for several hours, and organic/inorganic hybrid photoelectrodes (e.g. polymer coated photoelectrodes) also has a limited durability. Therefore, it is challenging to develop a facile but effective approach for stabilizing the photoelectrodes. In this work, we induced a handful of cheap urea into the Ni,Fe-based hydroxides as robust and conformal OECs layers, deposited on the BiVO4 photoanodes by an one-step impregnation process. Urea, an assisted nitrogen/carbon source, played an active role on the uniform growth of ultrathin OEC layer, replacing the complex organic cocatalyst. The thickness of urea induced Ni,Fe-based OEC could be modified by tuning the amount of urea, thereby improving the carrier dynamics and protecting photoelectrodes from photocorrosion. The presence of urea facilitates to deposit a homogeneous cocatalyst layer with higher electron transfer than the absence of urea, resulting in a high electrocatalytic OER and PEC performance. The optimized urea-NiFeOOH/BiVO4 photoanode showed a photocurrent density of 4.8 mA cm−2 at 1.23 VRHE with impressive stability over 40 h at a potential of 0.8 VRHE, which is one of the best PEC stabilities using NiFe-based OECs on BiVO4. Benefiting from the strong coordination bond between the metal ions and urea, the C and N elements remained stable in the OEC layer before and after PEC test. This work presents a potential application using cheap, non-precious metal based electrocatalysts to overcome the bottle-necks limiting a long-term stability of PEC water splitting.

Front solar illumination on BiVO4 is becoming important to design tandem structures in photoelectrochemical (PEC) water splitting. However, the interfacial recombination of BiVO4/substrate (e.g. FTO) is more serious than the bulk/surface recombination, which influences the electron transfer to the back side for hydrogen reaction. The BiVO4 electrode therefore requires back illumination to obtain the best photoresponse. In this context, we proposed a universal strategy by applying a PdO layer functionalized SnO2 interface as a useful electron transport layer to strikingly reduce the interface recombination. A trace amount of Pd was doped in the bulk BiVO4 to modify the electronic structure by inducing a stronger dopant-host interaction than that of the surface-modified electrode and homogenous doping. The BiVO4/PdO electrodes exhibited similar PEC performance under both front and back illumination. The champion cocatalyst-free photoanode showed a record-high photocurrent of 4.90 mA cm−2 at 1.23 VRHE with a low onset potential of 0.15 VRHE in borate buffer electrolyte under AM 1.5 G front-illumination, accompanying with solar conversion efficiency of 1.72% at 0.6 VRHE. Equally importantly, a sustained long-term photostability over 80 h was achieved, which is the best performance and stability reported among the cocatalyst-free BiVO4 photoelectrodes from front illumination. This work will open a new avenue for high-stability-performance photoelectrode design.

Engineering the interfacial structure of hybrid catalysts is crucial for enhanced electrocatalytic performances. Herein, a new strongly heterogeneous catalyst of Co/CoO/Co(OH)2 nanowires with proper interfacial structure was synthesized via a plasma etching approach. X-ray photoelectron spectroscopy and electron energy loss spectroscopy revealed that strong chemical couplings at the hybrid interface induced fast charge transfer, leading to considerable amounts of Co2+/Co sites present in the hybrid. The high conductivity from metal Co and one dimensional nanostructure favored the electron transfer and electrolyte access. The metallic Co was further oxidized to Co2+/Co3+ to address instability under applied potential during long-term testing. The resulting catalyst exhibited an excellent overpotential of 266 mV at 20 mA cm−2 and a Tafel slope of 85 mV dec−1 in alkaline medium. Importantly, the hybrid Co/CoO/Co(OH)2 demonstrated a super long-term durability over 200 h among the most ultra-long stability Co-based OEC catalysts. This catalyst was applied on light absorbing BiVO4 for solar-driven water splitting, exhibiting a significantly enhanced photoelectrochemical (PEC) activity, 5.32 mA cm−2 obtained at 1.23 VRHE, which represented one of the best performances achieved by Co-based OER cocatalysts.

A novel series of 4-substituted-piperazine-1-carbodithioate derivatives of 2,4-diaminoquinazoline were synthesized and tested for their antiproliferative activities against five human cancer cell lines including A549 (lung cancer), MCF-7 (breast adenocarcinoma), HeLa (cervical carcinoma), HT29 and HCT-116 (colorectal cancer). Most of the synthesized compounds showed broad spectrum antiproliferative activity (IC50 1.47–11.83 μM), of which 8f, 8m and 8q were the most active members with IC50 values in the range of 1.58–2.27, 1.84–3.27 and 1.47–4.68 μM against five cancer cell lines examined, respectively. Further investigations revealed that compounds 8f, 8m and 8q exhibited weak inhibition against dihydrofolate reductase and no activity against thymidylate synthase, while induced DNA damage and activated the G2/M checkpoint in HCT-116 cells.