Charge-Carrier Dynamics at the CuWO₄/Electrocatalyst Interface for Photoelectrochemical Water Oxidation

Abstract

Unraveling the charge-carrier dynamics at electrocatalyst/electrode interfaces is critical for the development of efficient photoelectrochemical (PEC) water oxidation. Unlike the majority of photoanodes investigated for PEC water oxidation, the integration of electrocatalysts with CuWO4 electrodes generally results in comparable or worse performance compared to the bare electrode. This is despite the fact that the surface state recombination limits the water oxidation efficiency with CuWO4 electrodes, and an electrocatalyst ought to bypass this reaction and improve performance. Here, we present results that deepen the understanding of the energetics and electron-transfer processes at the CuWO4/electrocatalyst interface, which controls the performance of such systems. Ni0.75Fe0.25O y (denoted as Ni75) was chosen as a model electrocatalyst, and through dual-working electrode experiments, we have been able to provide significant insight into the role of the electrocatalyst on the charge-transfer process at the CuWO4/Ni75 interface. We have shown a lack of performance improvement for CuWO4/Ni75 relative to the bare electrode to water oxidation. We attribute this surprising result to water oxidation on the CuWO4 surface kinetically outcompeting hole transfer to the Ni75 electrocatalyst interface.

Nature of Charge Carrier Recombination in CuWO4 Photoanodes for Photoelectrochemical Water Splitting

“…This value is in line with previous records for CuWO 4 -based electrodes prepared with different synthetic strategies ( Table 2 ). 41 , 42 However, it is far from the maximum photocurrent expected for the 2.2 eV band gap of CuWO 4 . Indeed, assuming that all absorbed photons in the CuWO 4 :580 electrode ( Figure 2 D) are completely converted into current would lead to a 5.6 mA cm –2 theoretical maximum photoresponse under 1 sun illumination.…”

Emergent CuWO4 Photoanodes for Solar Fuel Production: Recent Progress and Perspectives

“…The NiWO 4 has a distorted wolframite crystal structure similar to CuWO 4 and can form a type II heterojunction with CuWO 4 due to its higher energy CB and VB levels than those of CuWO 4 , reducing electron-hole recombination and improving IPCE [56]. P. Shadabipour et al [57] deposited a well-known Ni-and Fe-based co-catalyst on CuWO 4 , but the OER efficiency of Ni 0.75 Fe 0.25 O y /CuWO 4 did not significantly increase because photoexcited holes did not migrate efficiently and the reaction occurred preferentially on the CuWO 4 surface rather than on the co-catalyst.…”

Fast annealing fabrication of porous CuWO4 photoanode for charge transport in photoelectrochemical water oxidation

“…Among them, CuWO 4 is one of the most encouraging materials as photoanode owing to its reasonable narrow band gap (2.3 eV), and a maximum theoretical photocurrent density up to ∼9 mA cm −2 can be expected, similarly to the best-performing oxide photoanode candidate BiVO 4 [13]. Nevertheless, CuWO 4 manifest relatively low PEC performance and decorating CuWO 4 with most electrocatalysts has not shown for promoting the water oxidation efficiency unlike nearly all other photoanodes [14][15][16]. For example, an optimized oriented CuWO 4 film with a high exposure ratio of the (100) crystal facet presented a photocurrent density of 0.38 mA cm −2 under 1 sun illumination at +1.23 V versus the reversible hydrogen electrode (RHE) [17].…”