The fabrication of monolithic nanoporous zinc bears its significance in safe and inexpensive energy storage; it can provide the much needed electrical conductivity and specific area in a practical alkaline battery to extend the short cycle life of a zinc anode. Although this type of structure has been routinely fabricated by dealloying, that is, the selective dissolution of an alloy, it has not led to a rechargeable zinc anode largely because the need for more reactive metal as the dissolving component in dealloying limits the choices of alloy precursors. Here, we apply the mechanism of dealloying, percolation dissolution, to design a process of reduction-induced decomposition of a zinc compound (ZnCl2) for nanoporous zinc. Using naphthalenide solution, we confine the selective dissolution of chloride to the compound/electrolyte interface, triggering the spontaneous formation of a network of 70 nm wide percolating zinc ligaments that retain the shape of a 200 μm thick monolith. We further reveal that this structure, when electrochemically oxidized and reduced in an alkaline electrolyte, undergoes surface-diffusion-controlled coarsening toward a quasi-steady-state with a length scale of ∼500 nm. The coarsening dynamics preserves the continuous zinc phase, enabling its uniform reaction and 200 cycles of stable performance at 40% depth of discharge (328 mAh/g) in a Ni–Zn battery.

The beauty of dealloying, i.e., the selective dissolution of an alloy, lies in the spontaneous formation of bicontinuous nanoporous metal, whose robustness, conductivity, and high specific area are otherwise difficult to achieve in a monolithic form. However, a uniform structure of nanoporous metal requires a homogeneous alloy precursor, whose laborious fabrication has been limiting the application of dealloying and dealloyed materials. Here, we replace the alloy precursor with a compound, and design another type of selective dissolution, reduction-induced decomposition (RID). Using the RID of AgCl as an example, we chemically reduced bulk AgCl samples to create bicontinuous nanoporous Ag that resembles dealloyed structures. The monolithic material possesses a uniform ligament width of 72 nm and a specific area of 7.57 m2/g. The ligament width can be tuned in a range from 30 nm to 1 μm through coarsening, and the porosity from 57% to 87% by replacing silver cations in the compound with sodium cations. The RID of this multication compound can lead to a hierarchical structure, which evolves because of two simultaneous percolation dissolutions. The hierarchical nanoporous Ag delivered a stable performance as a high-capacity Ag/Ag x O electrode owing to its micron-sized pores for fast mass transfer. RID not only provides an inexpensive alternative to dealloying, it also expands the design space of nanoporous materials for meeting diverse needs in electrochemical applications.

The need for cost-effective, safe energy storage has led to unprecedentedly complex designs of materials and structures to meet stringent requirements. Yet, it remains a question whether we can eventually afford the manufacturing of these new materials and structures at a practical cost. Here, we introduce a new approach toward an all-organic aqueous battery through one-step, solution-phase adsorption. In this battery, two quinone molecules with different redox potentials adsorb onto two porous carbon electrodes to serve as the negative and the positive electrodes. For the negative side, cyclic voltammetry shows a high surface coverage of 66 pmol/cm2 for the adsorbed quinone (anthraquinone-2,7-disulfonate), which enables a stable capacity of 77 mAh/g. The full battery, operating in 1 M sulfuric acid, delivers more than 80% of its capacity at rates of up to 60C, and it retains more than 70% of the capacity after 600 cycles. As the battery adopts the typical build of a supercapacitor, this adsorption-based approach should apply broadly to achieve low-cost, safe storage. The work also provides a quantitative account of the electrochemistry of quinone adsorbed on carbon, which bears significance in the exploitation of quinone molecules in various electrochemical applications.