A new class of materials that can passively harvest water from air

Original Article ↗ Hacker News Discussion ↗

Comparison to existing moisture-removal tech

  • Many comments liken this to “high‑tech dehumidifier bags” (silica gel, calcium chloride, desiccant dehumidifiers).
  • Key claimed difference: this material both absorbs water and then expels it as surface droplets without chemical consumption, potentially allowing continuous cycling rather than regeneration by heating.
  • Others point out we already have passive/low‑power systems (air wells, fog collectors, Persian cooling towers, desiccant systems), so the question is whether this offers a real energy or performance advantage.

Thermodynamics and “physics‑defying” debate

  • Multiple commenters stress that condensing water from unsaturated air cannot be free: latent heat (~2259 kJ/kg) must go somewhere, and entropy must not decrease overall.
  • Several argue that forming macroscopic droplets at constant temperature and <100% RH, as claimed, would violate the second law unless:
    • There is an unnoticed temperature/pressure gradient, or
    • The material is acting as a finite energy/entropy sink and will saturate.
  • Capillary condensation in tiny pores at <100% RH is accepted; what’s disputed is spontaneous extrusion of liquid to convex droplets on a surface without external work or cooling.
  • Others counter that the experiments used active temperature control, so latent heat is being removed by the apparatus; in principle, similar heat could be dumped passively to a heat sink (ground, night sky, radiative surface).

Critique of university PR and wording

  • Strong pushback on phrases like “defies the laws of physics” and “no external energy,” seen as sensational and scientifically misleading.
  • Several note that university PR offices often overhype incremental results, and readers are urged to look at the actual paper rather than the press release.

Experimental constraints and unknowns

  • From the paper: visible droplets only at very high RH (~90–97%) and on nano‑structured films; unclear performance at typical indoor or arid conditions.
  • Rate of water production per area is not reported in the popular write‑ups; commenters see this as crucial and currently unknown.
  • Droplets are strongly pinned to the surface; there is no demonstrated low‑energy method to collect bulk water at scale.
  • Longevity, fouling (dust, microbes, biofilm), and real‑world durability are flagged as open questions.

Potential applications (if the physics and engineering pan out)

  • Quieter, lower‑energy dehumidification for homes and AC systems; could reduce mold and improve comfort where humidity is high.
  • Passive or low‑power water harvesting in humid but water‑scarce regions, or as an add‑on to existing cooling infrastructure.
  • Localized water supply for crops, trees, or remote installations; some speculate about coupling with simple mechanics (moving belts, wicks, ultrasound) to strip droplets.
  • Several commenters note that atmospheric water harvesting is intrinsically more energy‑intensive than desalination per liter; any use would likely be niche or location‑driven, not a universal water solution.

System‑level and environmental concerns

  • One thread worries that large‑scale atmospheric water harvesting could alter regional rainfall patterns by “stealing” moisture upstream, though this remains speculative and unquantified in the discussion.
  • Others note that anything persistently wet will attract dust and microbes; biofouling could severely degrade performance outside lab conditions.

Overall sentiment

  • The underlying nano‑scale wetting behavior is seen as scientifically interesting and possibly useful.
  • However, many commenters are skeptical that it is close to a practical, physics‑beating “passive water harvester” as implied by the PR; key metrics (energy balance, throughput, scalability, collection method) remain unclear.