Electrified carbon capture and release holds promise in carbon management; but it is constrained by high energy demand. Here, we studied two candidate systems for electrochemical CO ₂ release from a direct air capture (DAC) postcapture liquid: The first, a hydrogen loop cell, is electricity-efficient, but its evolved CO ₂ is mixed with H ₂ , introducing a 3 to 4 GJ/tonCO ₂ additional energy separation cost. The second system, a solid-state metal oxide redox couple (proton sponge), avoids the gas separation challenge but is stable only in the bicarbonate and not the highly alkaline regime. These considerations led us to examine a two-stage system: An efficient hydrogen loop would first downshift the pH from 13.5 to 9; and a second metal oxide would be used to release CO ₂ from bicarbonate. We report an electrified process that provides the release of a pure CO ₂ stream from a post-DAC liquid with a measured total energy of ~4.5 GJ/tonCO ₂ : 2.4 GJ from the H ₂ looping stage and 2.1 GJ from the MnO ₂ -based stage—substantially lower than the >=10 GJ/tonCO ₂ required by pH-swing methods such as bipolar membrane electrodialysis. We conclude with a generalized analysis of how staged pH downshifting reduces the overall Nernst voltage penalty and facilitates energy-efficient CO ₂ release.

Cost-effective alkaline water electrolysis requires non-precious-metal electrocatalysts that sustain the hydrogen evolution reaction (HER) at high current densities while maintaining favorable interfacial kinetics and an accessible electrode structure. Here, Co incorporation was used to suppress the long-range crystalline order of Fe and generate poorly crystalline Fe-Co aerogels through one-pot NaBH₄ reduction, gelation, and freeze-drying. A Fe_100−xCo_x series (x = 0, 60, 80, and 100; nominal feed compositions) was examined to determine how composition-induced structural changes affect network morphology, interfacial accessibility, and high-current HER behavior. Among the series, FeCo60-A formed the finest interconnected particle network and exhibited the largest BET surface area (34.1 m² g⁻¹), a high double-layer capacitance (1.04 mF cm⁻²), and the smallest apparent Nyquist arc. After iR correction, it required overpotentials of 345, 520, and 685 mV to reach 100, 500, and 1000 mA cm⁻², respectively, and maintained a nearly constant potential during 24 h operation at −1000 mA cm⁻² while largely retaining its interconnected porous morphology. These results demonstrate that Co incorporation into the Fe-based aerogel framework effectively tunes structural order and interfacial characteristics, enabling improved HER performance under high-current alkaline conditions.

Electrochemical nitrate reduction can combine nitrogen removal with ammonia recovery, but the contribution of an aerogel network is difficult to separate from changes in catalyst chemistry and electrode preparation. This review examines when the architecture created by gelation and drying remains relevant after electrode fabrication and during nitrate conversion. Metallic, carbon-based, and hybrid aerogels are compared through their preparation, working-state structure, reaction evidence, and operating conditions. Particular attention is given to nitrate activation, downstream hydrogenation, soluble-intermediate retention, and competition with hydrogen evolution and nitrogen formation. Related non-aerogel studies provide mechanistic and reactor comparisons while retaining their distinct material identities. The analysis separates measured responses from proposed pathways and distinguishes peak Faradaic efficiency from sustained conversion and product recovery. Dry surface area, isolated spectroscopic signals, and performance measured under different conditions do not independently establish an aerogel-specific advantage. Priorities emerging from the literature are comparisons of retained and fragmented networks, coupled measurements of intermediate transport and catalyst reconstruction, and nitrogen balances under defined feed and recovery conditions. These comparisons provide a basis for evaluating which aerogel design features remain useful in a working nitrate-conversion device.