Integrated Bundle Electrode with Wettability-Gradient Copper Cones Inducing Continuous Generation, Directional Transport, and Efficient Collection of H₂ Bubbles

Abstract

The hydrogen evolution reaction (HER), as an efficient process of converting various energies into high-purity hydrogen, has attracted much attention from both scientific research studies and industrial productions. However, its wide applications still confront considerable difficulties, for example, bubble coverage on the electrode and bubble dispersion in the electrolyte, which will disturb current distribution and isolate active sites from reaction ions resulting in a high reaction overpotential and large Ohmic voltage drop. Consequently, timely removing the generated gas bubbles from the electrode as well as avoiding their direct release into the electrolyte can be an effective approach to address these issues. In this work, we have developed an elegant electrode, that is, the integrated bundle electrode with wettability-gradient copper cones, which is endowed with the multifunctions of continuous generation, direct transport, and efficient collection of hydrogen bubbles. All processes are proceeding on the electrode, which not only remove the generated hydrogen bubbles efficiently but also prevent the hydrogen bubbles from releasing into the electrolyte, which should greatly advance the development of water electrolysis and offer inspirations for people to fabricate more efficient HER devices.

Ultraviolet-Driven Janus Foams with Wetting Gradients: Unidirectional Penetration Control for Underwater Bubbles

“…The bubbles with small curvature radius (1, 2, 3, 2 + 3, 4) can only adhere to the UV-15 surface instead of penetrating upward until the bubbles reached a certain curvature radius (2 + 3+4). Underwater, the hydrophobic surface shows high adhesion to micro/nanosized bubbles, and the bubbles trapped on the hydrophobic surface are inclined to adhere on its surface. , In this case, bubble penetration requires a sufficient driving force to overcome the resistance of adhesion. With the continuous injection of bubbles, the bubbles penetrating the upper surface formed an air bulge until the buoyancy was sufficient to escape the upper surface (Movie S2).…”

“…In recent years, underwater bubble manipulation has successfully accomplished the transportation and efficient collection of bubbles on surfaces with special wettability. − Controlling the movements of underwater bubbles can be effectively achieved on superhydrophobic surfaces ,, and lubricant-infused surfaces , as a result of their high adhesion forces to bubbles and aerophilicity in liquids . On these special wetting surfaces, three main forces driving and controlling the transport of bubbles were widely discussed: buoyancy, wetting gradient, and Laplace pressure difference. ,− Besides, the Janus membrane with a wettability gradient on two opposite surfaces has exhibited favorable advantages in terms of bubble penetration and transport.…”

Tailoring 3D-Printed Electrodes for Enhanced Water Splitting

“…Detailed properties of these patterns are shown in Table S1. These patterns, adopted following recent electrode studies, 19,21,22,38 approximately double the exposed geometric area compared to planar electrodes, thereby increasing contact between the Ni active sites and the electrolyte. 21 The surface roughness of these patterns was measured by NCP from 3D surface images (Figure 3b, see also Figure S9).…”

Passive Automatic Switch Relying on Laplace Pressure for Efficient Underwater Low-Gas-Flux Bubble Energy Harvesting

“…Movement of bubbles driven by surface tension usually occurs on the surfaces of special geometric structures or materials with wettability gradients . For example, a bubble on the surface of a hydrophobic conical thorn can spontaneously move from the tip to the root of the thorn driven by Laplace pressure. , Similarly, a bubble attached to the surface of a wedge-shaped hydrophobic structure can automatically move from the narrow end to the wide end. − In neither of these cases can the bubble move in the opposite direction. In addition to geometric gradients, wettability gradients can also generate a Laplace pressure on the surface of a bubble, enabling it to spontaneously move from the hydrophilic (aerophobic) side to the hydrophobic (aerophilic) side without reverse transport. , A Janus membrane with one hydrophilic surface and one hydrophobic surface is able to achieve unidirectional penetration of bubbles. − In the interface mechanical behaviors of these bubble-manipulation structures, Laplace pressure drives the bubbles to automatically move along the direction of geometric or wettability gradient, and it prevents reverse movement.…”