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Graphical abstract A quasi-solid-state tandem photoelectrochemical fuel cell that yields an open circuit voltage of 0.78 V and a maximum power density of 130 μW·cm−2 was assembled by utilizing hydrogel electrolyte, Au-TiO 2 NRAs photoanode and pTTh-Cu 2 O pohotocathode. The pTTh-layer protected Cu 2 O exhibited remarkably improved photostability as well as achieved significantly accelerated oxygen reduction reaction performance. Highlights • A quasi-solid-state tandem photoelectrochemical fuel cell was fabricated. • Polyterthiophene coated p-type cuprous oxide was prepared as photocathode. • Photocathode exhibited improved anti-photocorrosion and photocatalytic activity. • Gold nanoparticles decorated TiO 2 nanorod arrays was presented as photoanode. Abstract Photoelectrochemical fuel cells (PFCs) serve as a model system for harvesting electric energy from solar and biomass based on anodic fuel oxidation and cathodic oxygen reduction reaction (ORR). However, the sluggish ORR thereby limits the performance of PFC. Herein, we present a novel photocathode with polyterthiophene (pTTh) coated p-type cuprous oxide (Cu 2 O) (pTTh-Cu 2 O) that achieves boosted ORR kinetics, as well as exhibits remarkably improved photostability. By utilizing a hydrogel electrolyte which can avoid the leakage and volatilization of liquid electrolyte, a quasi-solid-state PFC device with eminent stability that consists of gold nanoparticles (Au NPs) decorated TiO 2 nanorod arrays (Au-TiO 2 NRAs) photoanode and pTTh-Cu 2 O photocathode can be assembled. And the fabricated PFC exhibits outstanding performance that yields an open circuit voltage of 0.78 V and a maximum power density of 130 μW·cm−2 utilizing glucose as feeding under illumination. Furthermore, the as-prepared quasi-solid-state PFC demonstrates its potential for practical application by lighting a commercial light-emitting diode (LED). It is our believe that such rational design not only can be expanded for organic wastes degradation and water splitting, but also shed a light on the development of portable electronics driven by solar. [ABSTRACT FROM AUTHOR]

• A tandem photoelectrochemical cell was designed for bias-free overall solar water splitting. • ZIF-67 decorated WO 3 photoanode exhibited superior photoelectrochemical performance. • Z-scheme black phosphorus/BiVO 4 photocathode was presented. • The pseudo-capacitive WO 3 photoanode makes it possible to realize round-the-clock hydrogen production. Photoelectrochemical (PEC) cell, representing as one of the most promising candidates to implement solar-driven unassisted overall water splitting, still remains a bottleneck in the construction of technology strategies for efficient solar energy utilization due to the intermittent nature of sunlight. Herein, we demonstrate an approach to realize round-the-clock hydrogen production by a solar rechargeable tandem PEC cell with two photoactive electrodes, where the photoanode is composed of a pseudocapacitive WO 3 nanoflakes film sensitized with visible-light responsive zeolitic-imidazolate-framework-67 (ZIF-67), and the photocathode is constituted with a Z-scheme BiVO 4 -black phosphorus (BP) heterojunctions that can broaden the light absorption to near-infrared (NIR) region as well as maintain the strong redox ability to fasten hydrogen evolution reactions by the effective charge separation. Deliberately, the alignment of Fermi level between the as-prepared WO 3 -ZIF-67 photoanode and BiVO 4 -BP photocathode permits us to realize a tandem PEC cell with reversible electron storage property, enabling light-induced charge storing and on-demand release in the dark, for the application of unassisted overall water splitting. The formed tandem PEC cell shows a promising strategy for the conversion of solar power into hydrogen fuel by integrating pseudocapacitive materials into man-made photovoltaic cells, and provides a new guidance for the design of multi-functional PEC device. [ABSTRACT FROM AUTHOR]

[Display omitted] • A paper-based photoanode is developed for photoelectrochemical water splitting. • MoSe 2 nanosheet anchored CdS-ZnO array functional paper is prepared. • Tandem Z-scheme configuration with double IEFs and photothermal effect are integrated. • The flexible photoanode achieves admirable solar water splitting performance. Rational design of photoelectrode architectures is deemed as an effective solution to enhance efficiency of photoelectrochemical water splitting for conquering increasingly prominent environmental problems. Herein, a programmable flexible photoanode with built-in tandem Z-scheme configuration fabricated by in-situ growth of MoSe 2 -CdS-ZnO array with ultrathin nanosheet-interlaced-nanorod structure on the Au paper electrode, is firstly reported. By taking advantages of the interwoven nanonetwork structure, high conductivity as well as larger porosity of the as-fabricated Au paper electrode, a stable light-harvesting paper chip with fast transfer/separate mediators of the charge/carriers is thus integrated. By virtue of double internal electric fields (IEFs) and photothermal effect, the developed MoSe 2 -CdS-ZnO photoanode exhibits incident-photon-to-current efficiency of 52 % under 460 nm of light irradiation, and the current density reaches 2.4 mA cm−2 at 0.3 V versus normal hydrogen electrode, which is comparable with respect to current state-of-the-art "type-II-scheme", "surface-scheme", and cocatalyst-free photocatalysts (0.03–2.4 mA cm−2). Consequently, the paper-based photoanode achieves admirable photoelectrocatalytic hydrogen generation property (39.7 μmol cm−2 h-1). The synergistic effect of tailorable tandem Z-scheme configuration with double IEFs and delineating of 3D cross-linked network structure of the proposed photoanode in this work may open an avenue for constructing high-performance photoelectrochemical water splitting devices. [ABSTRACT FROM AUTHOR]