Powerful Thermogalvanic Cells Based on a Reversible Hydrogen Electrode and Gas-Containing Electrolytes

Thermogalvanic cells (TGCs) directly convert waste heat to electricity, but the efficiency has been limited largely by the contradiction between thermal resistance and electrical conductance. Here we report a new design of TGC that can disentangle such a dilemma and thus accelerate the thermoelectric conversion. The key is to replace the traditional liquid-based redox reaction and single-phase mass transport with an internal gas/liquid two-phase system. We choose the rapid H2/H+ redox reaction that generates H2 gas at the hot electrode while consuming it at the cool electrode. Between the electrodes is a 3D-printed thin separator comprising straightly aligned H2/electrolyte microchannels for fast H2/H+ transport. Besides gaining additional entropy from the water-vaporizing effect, such a gas-containing electrolyte layer, albeit only 0.36 mm in thickness, has diminished the heat convection between electrodes. The power density of this TGC reaches 4 W/m2 at a temperature difference of 30 K.