Boosting the Activity and Stability of Copper Tungsten Nanoflakes toward Solar Water Oxidation by Iridium-Cobalt Phosphates Modification

Abstract

Severe interfacial electron–hole recombination greatly limits the performance of CuWO4 photoanode towards the photoelectrochemical (PEC) oxygen evolution reaction (OER). Surface modification with an OER cocatalyst can reduce electron–hole recombination and thus improve the PEC OER performance of CuWO4. Herein, we coupled CuWO4 nanoflakes (NFs) with Iridium–cobalt phosphates (IrCo-Pi) and greatly improved the photoactivity of CuWO4. The optimized photocurrent density for CuWO4/IrCo-Pi at 1.23 V vs. reversible hydrogen electrode (RHE) rose to 0.54 mA∙cm−2, a ca. 70% increase over that of bare CuWO4 (0.32 mA∙cm−2). Such improved photoactivity was attributed to the enhanced hole collection efficiency, which resulted from the reduced charge-transfer resistance via IrCo-Pi modification. Moreover, the as-deposited IrCo-Pi layer well coated the inner CuWO4 NFs and effectively prevented the photoinduced corrosion of CuWO4 in neutral potassium phosphate (KPi) buffer solution, eventually leading to a superior stability over the bare CuWO4. The facile preparation of IrCo-Pi and its great improvement in the photoactivity make it possible to design an efficient CuWO4/cocatalyst system towards PEC water oxidation.

Ternary Ti–Mo–Fe Nanotubes as Efficient Photoanodes for Solar-Assisted Water Splitting

“…The transient photocurrent response to the on/off illumination as well as its decay mainly depend on the photogeneration/relaxation mechanism of the e – /h + pairs. − The initially originated photocurrent ( I i ) upon illumination can be attributed to the separation of photogenerated charge carriers at the semiconductor/electrolyte interface (SEI). Then, the photogenerated electrons transfer to the back contact, while the photoinduced holes move to the electrolyte to oxidize H 2 O. ,− By this time, a gradual decrease of the photocurrent is established until reaching a steady-state photocurrent ( I f ). , The photocurrent decay indicates charge carriers recombination. Upon light-off condition, the trapped holes at the semiconductor surface and the photogenerated electrons recombine. , The transient photocurrent can be calculated using eq : where t is the time, τ is the transient time constant, and the parameter D is given by eq : where I t is the current at any time t , I i is the initial spike current, and I f is the steady-state current.…”

“…Then, the photogenerated electrons transfer to the back contact, while the photoinduced holes move to the electrolyte to oxidize H 2 O. ,− By this time, a gradual decrease of the photocurrent is established until reaching a steady-state photocurrent ( I f ). , The photocurrent decay indicates charge carriers recombination. Upon light-off condition, the trapped holes at the semiconductor surface and the photogenerated electrons recombine. , The transient photocurrent can be calculated using eq : where t is the time, τ is the transient time constant, and the parameter D is given by eq : where I t is the current at any time t , I i is the initial spike current, and I f is the steady-state current. The transient time constant (τ) might be considered as the charge carrier’s lifetime and generally could be described as the time at which ln D = −1, as shown in Figure b. ,, It is worth mentioning that when the transient time constant increased, the recombination processes get delayed.…”

“…98,100−102 By this time, a gradual decrease of the photocurrent is established until reaching a steady-state photocurrent (I f ). 103,104 The photocurrent decay indicates charge carriers recombination. Upon light-off condition, the trapped holes at the semiconductor surface and the photogenerated electrons recombine.…”

“…Upon light-off condition, the trapped holes at the semiconductor surface and the photogenerated electrons recombine. 103,104 The transient photocurrent can be calculated using eq 5: 96…”

Oriented CuWO4 Films for Improved Photoelectrochemical Water Splitting

“…4−6 However, poor bulk charge transport and surface water oxidation activity limit the performance of CuWO 4 for PEC water splitting. 5,7 Many studies have been conducted on doping, 8,9 oxygen vacancies, 10−12 heterojunctions 13−15 and cocatalysts 16,17 to optimize its existing problems. 13,14,17−19 Doping with other elements can improve the conductivity by increasing the carrier density.…”