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The ever-increasing energy consumption stimulated the development of various solar energy conversion systems. Photocathodic protection (PCP), emerges as a promising photoelectrochemical technology to alleviate metal corrosion, but the centralization of all core reaction steps on one photoelectric-conversion-unit induces extremely low energy conversion efficiencies. Herein, a proof-of-concept modular PCP device incorporating electron transport layer (ETL), photoelectric conversion layer (PCL), hole transport layer (HTL) and hole consumption layer (HCL) is fabricated to delocalize the key reaction steps for the first time. Such a unified ETL/PCL/HTL/HCL architecture facilitates the efficient extraction of photoexcited electrons from the small-gap PCL to the protected metal through ETL, and holes to HCL for water oxidization through HTL. The directional "macroscopic" charge migration, prolonged charge lifetime and accelerated water oxidation lead to significantly improved PCP effectiveness in simulated seawater. Our findings provide a groundbreaking PCP design, allowing fine-tuning individual functional modules and inter-modular interfaces to vastly elevate performance. [Display omitted] • A photocathodic protection system with multi-module architecture was fabricated. • The key photoelectrochemical reaction steps were delocalized to separate modules. • The directional charge flow was maintained through the whole unified device. • Vastly improved energy conversion efficiency than conventional design was achieved. • A groundbreaking design strategy for photocathodic protection systems is provided. [ABSTRACT FROM AUTHOR]

One of the major problems for seawater electrolysis is chloride corrosion arising from the chlorine oxidation reaction (ClOR). Although researchers have endeavored to improve the OER activity (overpotentials below 490 mV) to avoid the ClOR, an OER deactivation effect of chloride anions still looms large even before the ClOR becomes a serious issue, and its mechanism remains unclear. Herein using a simple Fourier transform ac voltammetry (FTacV) method, we unveil a hidden fact about the detrimental effect of Cl- over an exemplar catalyst NiFe (oxy)hydroxide: it increases the formation potential of Ni(IV) thus lowering the OER performance. This is borne out by theoretical calculations, which reveal changes in the electronic environment of Ni sites induced by replacing the bridge OH- species with Cl- and the resulting difficulty to form high-valence Ni(IV). The consequence is a large increase in energy barrier of the OH* deprotonation step that lowers the OER activity. The poison effect of Cl- can be restrained by adding carbonate ions, which restores the facile formation of Ni(IV) and stabilizes the electrode for over 140-h saline water oxidation reaction at the current density of 100 mA cm−2. This work helps to guide the design of active and durable seawater-splitting electrocatalysts. [Display omitted] • We report the chloride anions' poison effect and the OER deactivation mechanism in simulated seawater for the first time. • Active Ni(IV) intermediates in NiFe catalysts are observed during OER using the simple FTacV electrochemistry method. • The chlorine anions increase the formation potentials of Ni(IV) intermediates and result in the decreased OER performance. • Carbonate ions counteract chlorine's impact, ensuring electrode stable for 140-h saline water oxidation at 100 mA cm−2. [ABSTRACT FROM AUTHOR]