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Chlor-alkali electrolysis is a key industrial process for the production of chlorine gas, caustic soda, and hydrogen fuels. Here, we demonstrate that a Ti foam electrode, which has a diffusion layer of liquid reactant, deposited with a thin layer of core/shell-structured mixed metal oxide nanoparticles enables almost zero polarization in the range of hundreds of mA cm−2 towards the chlorine evolution reaction (CER), using noble-metals 20 times lower than commercial electrode. The fast charge-transfer kinetics induce near-zero overpotential at low current densities, while the high mass transport rates aided by porous channels lead to unprecedentedly high CER performance (LSV derived overpotentials of 9 and 44 mV at 10 and 500 mA cm−2 with Faradaic efficiency of 99.1% and 86.1% in 5.0 M NaCl). Under practical chlor-alkali process conditions, the RNTO/Ti foam exhibited remarkable performance as a bifunctional electrode for CER and hydrogen evolution reaction (HER) with overpotential of 11 mV for HER. [Display omitted] • Core/shell-structured Ru-Ti-Nb mixed oxides exhibit superior durability at high current densities. • Liquid-diffusion electrode enables near-zero polarization for CER regardless of current density. • Exceptionally high HER activity in chlor-alkali condition with an overpotential of 11 mV at 10 mA cm−2. • Chlor-alkali electrolyzer using RNTO/Ti foams as anode and cathode exhibits 1.84 V cell voltage at 100 mA cm−2. [ABSTRACT FROM AUTHOR]

In this study, we demonstrated high-rate H 2 generation by coupling with the sulfite oxidation reaction (SOR) as an alternative to the oxygen evolution reaction for solar H 2 production. The emerging and cost-effective molybdenum phosphide electrocatalyst was appropriately optimized and used as a bifunctional catalyst in an alkaline electrolyte for both SOR and HER. Powered by state-of-the-art perovskite–Si tandem photovoltaics, a remarkable photocurrent density of over 17 mA cm−2 was achieved in the HER coupled with the SOR. In addition to the significantly enhanced photocurrent, the SOR can further reduce the overall cost of solar H 2 production owing to the elimination of the expensive membranes required for H 2 and O 2 gas separation. Considering the high global demand for desulfurization via the SOR, the strategy proposed here will enable practical H 2 production from renewable sources while effectively converting the toxic SO 2 gas into a value-added product for the chemical industry. Solar hydrogen production system employing SOR as alternative anodic reaction is presented. Photoassisted electrochemical device consists of MoP-based catalysts and perovskite–Si tandem PV. Our system based on SOR demonstrates remarkable hydrogen generation photocurrent density of over 17 mA cm–2 under 1-sun illumination with prolonged durability of 50 h. [Display omitted] • Solar H 2 production employing SOR as an alternative anodic reaction is presented. • SOR enables the reduction in thermodynamic barrier for H 2 production. • Bifunctional MoP-based catalysts for SOR–HER is developed. • SOR-based PV-EC exhibits photocurrent of 17.23 mA cm–2 with durability of 50 h. [ABSTRACT FROM AUTHOR]

Ir and its oxide are the only available oxygen evolution reaction (OER) electrocatalysts with reasonably high activity and stability for commercial proton-exchange membrane electrolyzers. However, the establishment of structure–performance relationships for the design of better Ir-based electrocatalysts is hindered by their uncontrolled surface reconstruction during OER in acidic media. Herein, we monitor the structural evolution of two model Ir nanocrystals (one with a flat surface enclosed by (100) facets and the other with a concave surface containing numerous high-index planes) under acidic OER conditions. Operando X-ray absorption spectroscopy measurements reveal that the promotion of surface IrO x formation during the OER by the concave Ir surface with high-index planes results in a gradual OER activity increase, while a decrease in activity and limited oxide formation are observed for the flat Ir surface. After the activation process, the Ir concave surface exhibits ~ 10 times higher activity than the flat surface. Density functional theory computations reveal that Ir high-index surfaces are thermodynamically preferred for the adsorption of oxygen atoms and the formation of surface oxides under OER conditions. Thus, our work establishes a structure–performance relationship for Ir nanocrystals under operating conditions, providing new principles for the design of nanoscale OER electrocatalysts. Surface structure–controlled model Ir nanocrystals with flat and concave surfaces were designed as electrocatalysts for the oxygen evolution reaction under acidic conditions. The Ir concave surface containing high-index planes exhibited progressive activation during the oxygen evolution reaction due to the facile formation of active IrO x , while the flat surface showed a gradual decrease in activity. [Display omitted] • Surface structure–controlled model Ir nanocrystals with flat and concave surfaces. • The structural evolution of Ir catalysts under acidic oxygen evolution reaction. • The activation process of Ir concave surface containing high-index planes under OER. • The deactivation process of Ir flat surface during acidic OER. • The important role of high-index planes for promoting OER activity in acidic media. [ABSTRACT FROM AUTHOR]