Aqueous Zn ion-based fiber-shaped batteries (AZFBs) with the merits of high flexibility and safety have received much attention for powering wearable electronic devices. However, the relatively low specific capacity provided by cathode materials limits their practical application. Herein, we first propose a simple strategy for fabricating high-capacity Zn-iodine fiber-shaped batteries with a high concentration electrolyte and a reduced graphene oxide fiber (GF) cathode. It was found that oxygen functional groups in the graphene sheet demonstrate strong interaction with polyiodides but hinder electron conductivity; thus, the optimal balance between the specific capacity and coulombic efficiency of the GF electrode can be a function of the surface properties at different hydrothermal temperatures. Besides, the regulated high concentration electrolyte effectively suppresses the diffusion of polyiodides, which is attributed to the constrained freedom of water. More importantly, a four-electron redox mechanism was experimentally revealed through in situ Raman spectra. As a result, this fiber-shaped battery delivers a superior high reversible capacity of 390 mA h cm−3 at 1 A cm−3, an excellent rate performance of 125.7 mA h cm−3 at a high current density of 8 A cm−3 and outstanding cycling life with 82% capacitance retention after 2500 cycles.
Harnessing light to drive high-energy batteries is an intriguing goal, yet photoactivity often fails for reasons that have remained elusive, which is starkly exemplified in photo-assisted solid-state lithium-oxygen batteries. Here, we identify photo-shielding by opaque, ionically resistive discharge products as the critical, previously overlooked failure mechanism. This "catalyst blinding" effect not only blocks light but also passivates the electrochemical interface, causing a catastrophic kinetic shutdown. We overcome this limitation with a "hydro-photo-synergy" strategy, using controlled water vapor to shift the solid-state electrochemistry from a 2e− to an efficient 4e− pathway and transform the product into highly transparent, ionically conductive products. This dual optical and electrochemical enhancement sustains photocatalysis for deep and reversible reactions, unlocking a 2-fold increase in accessible capacity, a low overpotential (0.3 V), and outstanding stability (>170 cycles for 34 mAh cm-2). This work establishes in situ product engineering as a new paradigm to unlock high-energy solid-state photo-electrochemical devices.
Nonprecious-metal electrocatalysts have been intensively investigated, but how to keep a balance between their sustainability and competitive performance for the oxygen reduction reaction (ORR) is still a big challenge for energy applications. In this work, a type of bimetal- and nitrogen-codoped mesoporous carbon electrocatalyst (FeCo-N/C-800) was successfully synthesized via a simple hydrothermal method , followed by a calcination process at 800 °C in nitrogen atmosphere and an acid-etching process. The obtained FeCo-N/C-800 can act as a high-performance ORR catalyst with high onset and half-wave potentials (0.94 and 0.85 V), a large limiting current density (5.94 mA cm −2 ) and a four-electron reaction process in 0.1 M KOH solution, which can be comparable with commercial Pt/C catalyst. Additionally, the FeCo-N/C-800 exhibited superior long-term durability and high methanol tolerance. The excellent electrocatalytic performance of the FeCo-N/C-800 can be ascribed to the mesoporous structure (bimodal pores system), the synergetic interaction of the multiple ORR active sites, suitable N-doping level and the highly conductive carbon matrix. These structural features can promote efficiently the mass and electron transfer , provide abundant active sites for the adsorption and reaction of oxygen molecules, and thus improve the reaction kinetics. The present study not only provides a strategy for the synthesis of carbon-based electrocatalyst with high ORR catalytic activity and stability, but also demonstrates that the bimetal- and nitrogen-codoped carbon materials could be a class of competitive candidate for non-noble metal-based electrocatalysts.
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