Table 1 Comparison of energy transduction mechanisms for small-scale water energy harvesting

Phase-change–induced capillary flow

Gas, Liquid

• Humidity control

- arid to humid air

• Direct water stream

• - soak one side of the device in water

• Wettability

• Continuous water uptake dynamics

0.25–30

0.0063–101

^{17,18,19,20,21}

Ion concentration gradient

Gas

• Humidity control

• - arid to humid air

• Wettability

• Ion flux dynamics in active layer

0.01–25

0.0184–110

^{14,21,22,23,24}

Thermoelectric harvesting

Gas, Liquid, Solid

(Snow/Ice)

• Temperature gradient

- solar-driven steam

• - aboveground/subgrade

• Thermal coupling

• Optical/thermal properties

~10–200

~10–500

^25,26,27,28

Thermo-osmotic and thermoelectro-kinetic conversion

Gas, Liquid

• Temperature gradient

- water steam

• - hot/chilly water sinks

• Ionic Seebeck coefficient

• Soret-driven ionic migration

~0.09-1

~0.00008–5

^29,30,31,32

Electromagnetic transduction

Gas, Liquid

• Flow velocity

- vapor or water flow

• Rate of magnetic flux change

• Flow induced rotation speed

30–700

0.09–4

^{33,34,35,36,37,38}

Piezoelectric transduction

Liquid, Solid

• Mechanical oscillation

- vortex in fluid

- falling water droplets

• Strain amplitude

• Piezoelectric coupling

~0.13–0.5

0.0001–0.005

^{39,40,41,42,43,44}

Triboelectric transduction

Gas, Liquid,Solid

(Snow/Ice)

• Directional water flow

- rotation of wheel

- passing tap water

• Water wave

- reciprocation of tube

- rolling sphere ball

• Contact-separation dynamics

• Contact area

~0.03–200

~0.00005–1060

^{45,46,47,48,49,50,51,52,53,54,55,56}

Droplet-driven mechanisms

Liquid

• Collision of droplet

- impact & sliding droplet on device

• Motion of droplet

- oscillating droplet in device on wave

• Wetting dynamics

• Droplet sliding dynamics

1–20

0.01863–

2.6 × 10⁵

^{50,51,52,53,57,58,59,60,61,62,63,64,65}