Effectiveness of CuO Nanoparticle-Based p–n Bulk-Heterojunction Electrodes for Photoelectrochemical Hydrogen Generation

Abstract

Bulk-heterojunction (BHJ) electrodes are expected to play a significant role in electrode designs aimed to increase the efficiency of photoelectrochemical applications owing to their combined, efficient charge extraction and charge transportation. The photoelectrochemical behavior of BHJ nanoparticulate photoelectrodes with CuO (donor, p-type) and TiO 2 (acceptor, n-type) semiconductors is examined with a focus on random distribution nature. Electrodes with different donor/ acceptor ratios are prepared and characterized using various spectroscopic and electrochemical tools to reveal interconnected, crystalline, randomly distributed CuO (∼150 nm) and TiO 2 (∼25 nm) nanoparticles. A photocathodic current of ∼1.5 mA/ cm 2 is measured at 0 V RHE for CuO photocathodes (FTO/npCuO) under simulated sunlight (AM 1.5G) in 0.5 M Na 2 SO 4 (pH 5.5). We identify the cathodic photocurrent to be due to internal reduction of Cu 2+ to Cu + ; photocathodic hydrogen evolution was not observed. BHJ electrodes (FTO/npCuO:npTiO 2 ) display dual (p-type and n-type) semiconducting behavior and correspondingly exhibit cathodic and anodic photocurrents, the magnitude of which is dependent on the donor/acceptor ratio present. The addition of TiO 2 increases the electrode resistance and also promotes charge recombination in the photoelectrode. Compared to non-homogeneously distributed donor/ acceptor BHJ photoelectrodes, homogeneous electrodes obtained via the co-precipitation method exhibit higher photocurrents but still undergo photodegradation, implying the need for a protective layer or electron shuttle. We demonstrate photocurrents of 0.2 mA/cm 2 from TiO 2 -and Pt-protected npCuO:npTiO 2 BHJ photoelectrodes with improved stability and hydrogen evolution albeit with a low Faradaic efficiency (<30%).

Abnormal Photocurrent in Semiconductor p‐n Heterojunctions: Toward Multifunctional Photoelectrochemical‐Type Photonic Devices and Beyond

“…In fact, in recent years, using PEC principles, significant progress has been made in photonic devices with different material systems for various applications such as photodetection [6][7][8][9][10][11][12][13][14][15][16][17] and solar fuel production. [18][19][20][21][22][23][24][25] To realize multifunctionality in PECtype photonic devices, controlling the photocurrent polarity of the photoelectrode is a key. This further makes IIInitrides are particularly interesting.…”

“…In fact, in recent years, using PEC principles, significant progress has been made in photonic devices with different material systems for various applications such as photodetection [ 6–17 ] and solar fuel production. [ 18–25 ]…”

Employing bulk-heterostructure conductive polymer PFO/PFBT for the photoelectrochemical analysis of p-phenylenediamine

“…Bulk-heterojunction (BHJ), which holds promise as a potential renewable and economically viable energy source, plays an essential role in increasing the efficiency of photoelectrochemical applications. 21 Organic polymer semiconductors, especially polymers, with advantages of tunable band gap, broad light absorption spectra, highly optical absorption coefficient, solution processable fabrication, and good film forming properties have emerged as attractive candidates to construct bulk-heterojunction. [22][23][24] Photocurrent generation in organic bulk-heterojunction is most commonly understood as a photoinduced electron transfer (PET) process, which predominantly involves the photoexcitation of one semiconductor followed by electron transfer to the another.…”