Self-Powered Hydrogen Production with Improved Energy Efficiency via Polysulfides Redox

In the pursuit of efficient solar-driven electrocatalytic water splitting for hydrogen production, the intrinsic challenges posed by the sluggish kinetics of anodic oxygen evolution and intermittent sunlight have prompted the need for innovative energy systems. Here, we introduce an approach by coupling the polysulfides oxidation reaction with the hydrogen evolution reaction for energy-saving H2 production, which could be powered by an aqueous zinc-polysulfides battery to construct a self-powered energy system. This unusual hybrid water electrolyzer achieves 300 mA cm-2 at a low cell voltage of 1.14 V, saving electricity consumption by 100.4% from 5.47 to 2.73 kWh per m3 H2 compared to traditional overall water splitting. Benefiting from the favorable reaction kinetics of polysulfides oxidation/reduction, the aqueous zinc-polysulfides battery exhibits an energy efficiency of approximately 89% at 1.0 mA cm-2. Specially, the zinc-polysulfide battery effectively stores intermittent solar energy as chemical energy during light reaction by solar cells. Under an unassisted light reaction, the batteries could release energy to drive H2 production through a hybrid water electrolyzer for uninterrupted hydrogen production. Therefore, the aim of simultaneously generating H2 and eliminating the restrictions of intermittent sunlight is realized by combining the merits of polysulfides redox, an aqueous metal-polysulfide battery, and solar cells. We believe that this concept and utilization of polysulfides redox will inspire further fascinating attempts for the development of sustainable energy via electrocatalytic reactions.

Highly efficient conversion of surplus electricity to hydrogen energy via polysulfides redox

Decoupled electrolysis of water is a promising strategy for peak load regulation of electricity. The key to developing this technology is to construct decoupled devices containing stable redox mediators and corresponding efficient catalysts, which remains a considerable challenge. Herein, we designed a high-performance device, using polysulfides as mediators and graphene-encapsulated CoNi as catalysts. It produced H₂ with a low potential of 0.82 V at 100 mA/cm², saving 60.2% more energy than direct water electrolysis. The capacity of H₂ production reached 2.5×10⁵ mAh/cm², which is the highest capacity reported so far. This device exhibited excellent cyclability in 15-day recycle tests, without any decay of performance. The calculation results revealed that the electronic structure of the graphene shell was modulated by the electron transfer from N-dopant and metal core, which significantly facilitated recycle of polysulfides on graphene surfaces. This study provides a promising method for constructing a smart grid by developing efficient decoupled devices.

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A high-performance device of decoupled water electrolysis is constructed by using polysulfides as mediators and graphene-encapsulated CoNi as catalysts, which provides a new strategy to distribute the electricity reasonably by peak shaving and valley filling

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The potential of H₂ production only needs 0.82 V at 100 mA/cm² current density, which saves 60.2% more energy than direct electrolysis of water

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The capacity of the electrolyzer to produce voluminous hydrogen reaches 2.5 × 10⁵ mAh/cm² in a single pass, which is the highest capacity reported so far

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The device exhibits superior cyclicity in 15-days periodic recycle tests without any decay of performance