Gas Eruption Phenomenon Happening from Ga-In Alloy in Electrolyte

Gas Eruption Phenomenon Happening from Ga-In Alloy in Electrolyte Ruiqi Zhao,1,2 Hongzhang Wang,1,3 Jianbo Tang,1,3 Wei Rao,1,4,a) and Jing Liu,1,3,4,a)
1 Beijing Key Lab of CryoBiomedical Engineering and Key Lab of Cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China 2Department of Chemistry, University of Chinese Academy of Sciences, Beijing 100049, China 3Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084, China 4College of Future Technology, University of Chinese Academy of Sciences, Beijing 100049, China a) Authors to whom correspondence should be addressed. E-mail: weirao@mail.ipc.ac.cn; jliu@mail.ipc.ac.cn.
Abstract: We report a gas eruption phenomenon caused by electrolysis of liquid Ga-In alloy in an electrolyte, especially NaOH solution. A volcanic eruption-like blowout of gas occurred from the orifice on the alloy surface. In addition to gas plume, large gas bubbles were also generated and the total gas yield increased as In ratio was increased. It is found that destructiveness of the passivation layer on the Ga-In alloy is critical to gas generation. The mechanism of gas eruption can be ascribed to a galvanic interaction happens owing to passivation film and alloy with different activity connected as electrode in electrolyte. Further investigation demonstrated that the lattice of the film expands because of the incorporation of indium, which brings about the decrease in band gap and finally enhances more gas generation. These findings regain the basic understanding of room temperature liquid metal inside electrolyte.
Recently, studies on gallium-based liquid metals have drawn considerable attention, particularly for their potential applications in hydrogen generation. Such alloys have in fact been the focus of many studies. The addition of aluminum to Ga alloy contributes to self-driven motions.1-7 The majority of studies have proven the addition of aluminum or other metal particles as the main regulator of hydrogen generation.3, 8-14 The generation of gas is considered to be a propelling force of a bunch of phenomena, including the motion of Ga-In-Al in aqueous NaOH solutions,15 and the oscillation phenomenon of a copper wire embedded inside Ga-In-Al self-powering system.16 Alternatively, Ga–In liquid metal can be applied versatile to self-healing or contrast enhancement.17 Tang et al. showed that hydrogen could be generated from a drop of Ga-In alloy when left in contact with solid metal particles.18 However, phenomenon of gas evolution from bulk Ga-In alloy has always been overlooked and no studies have yet been reported. In this letter, we report an interesting gas eruption phenomenon occurring in Ga-In alloy when it contacts with an electrolyte. Over the experiment, 10 cm petri dish was pre-filled with 50 ml Ga-In alloy in the open air [Fig.1(a)], then 30 ml NaOH electrolyte was transferred onto the surface of alloy. When immersed in a 1 M alkaline electrolyte, a number of gas plumes appeared at the surface of GaIn10 (Ga : In = 9:1,w/w, see Fig.1(b) & Multimedia view), GaIn24.5 (Ga : In = 75.5:24.5, w/w, see Fig.S1& supplemental material S1) and GaIn50 alloy (Ga : In =1:1, w/w, see Fig.1(c) & Multimedia view). The eruption phenomena have been 2

recorded with a Canon EOS 70D camera with macro lenses. The experiments were performed at a temperature of 22°C.
The electrolyte activates the surface layer of Ga-In alloy and creates many orifices [Fig.1(d), side view in supplemental material S2], from which gas column pours out. In addition, the hydrogen gas generation is rapid and constant, and the continuous gas flow forms a gas plume in the electrolyte (see Multimedia view). This is a similar phenomenon to that of volatile gas blended with magma erupting from the seabed, which then rises to the top of sea water. Considering the similarities with submarine volcanic eruptions, we divide our eruption column into three zones19, namely regions of jet, ascent, and diffusion, respectively [Fig.1(e)]. The jet region is located at the lowest part of the eruption column, and the column width is approximately 50~200 μm. The gas flow from the orifice is sufficiently powerful to overcome the frictional resistance, and the velocity at the alloy/electrolyte interface is controlled mainly by the volatile gas release of the Ga-In alloy. In the ascent region (upper zone), the speed of the gas column is slower than that in the jet phase. The gas in the column scatters outward, and the force driving the upward motion is dominated by buoyancy. The diffusion region is located at the top of the eruption column where the eruption column rises and spreads in the horizontal direction. In diffusion region, the pressure of the eruption column and the external atmosphere reaches equilibrium.

FIG.1. Images of gas plumes and bubbles appearing on the

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