Electrochemical Generation of Individual Nanobubbles Comprising H₂, D₂, and HD

Abstract

The electrochemical reduction of deuterons (2D + + 2e − → D 2 ) at Pt nanodisk electrodes (radius = 15−100 nm) in D 2 O solutions containing deuterium chloride (DCl) results in the formation of a single gas nanobubble at the electrode surface. Analogous to that previously observed for the electrochemical generation of H 2 nanobubbles, the nucleation and growth of a stable D 2 nanobubble is characterized in voltammetric experiments by a highly reproducible and well-resolved sudden drop in the faradaic current, a consequence of restricted mass transport of D + to the electrode surface following the liquid-to-gas phase transition. D 2 nanobubbles are stable under potential control due to a dynamic equilibrium existing between D 2 gas dissolution and electrochemical generation of D 2 at the circumference of the Pt nanodisk electrode. Remarkably, within the error of the experimental measurement (<6%), the electrochemical current required to nucleate a D 2 gas phase in a D 2 O solution is identical to that for the H 2 gas phase in a H 2 O solutions, indicating that the concentration required for nucleating a D 2 nanobubble in D 2 O (0.29 M) is ∼1.25 times larger than that for a H 2 nanobubble (0.23 M), while the supersaturation is ∼300 in each case. We further demonstrate that individual nanobubbles can be electrogenerated in mixed D 2 O/H 2 O solutions containing both D + and H + at respective individual concentrations well below those required to nucleate a gas phase containing either pure D 2 or H 2 . This latter finding indicates that the resulting nanobubbles comprise a mixture of D 2 , H 2 , and HD molecules with the chemical composition of a nanobubble determined by the concentrations and diffusivities of D + and H + in the mixed D 2 O/H 2 O solutions.

Following Electroenzymatic Hydrogen Production by Rotating Ring–Disk Electrochemistry and Mass Spectrometry**

“…The probabilities of producing H 2 , HD (pathways 2 and 3 combined), or D 2 can be then expressed as a function of a KIE and the mole fractions, as outlined in the Supporting Information. [31] As shown in Figure 6 b, the KIEs for the overall CpI electrode as calculated for the observed product distribution are approximately 2 (for H 2 ), 2.3 (for HD), and 1.7 (for D 2 ). These values are in close agreement with the previously observed KIE of 1.8 for CpI using an electron mediator (methylviologen) and dithionite, [32] as well as the value of 2.5 recently observed for H + -dependent photo-driven formation of the Hred state of [FeFe]-hydrogenase from Clostridium acetobutylicum.…”

“…Here, we assume that hydrons are sequentially delivered to the Hcluster active site of CpI, 30 arriving at possible pathways for product formation of: The probabilities ( ) of producing H2, HD (pathways 2 and 3 combined) or D2 can be then expressed as a function of a KIE and the mole fractions ( 9), as outlined in the Supporting Information. 31 As shown in Figure 6b, the KIEs for the overall CpI electrode as calculated for the observed product distribution are ~2 (for H2), ~2.3 (for HD) and ~1.7 (for D2). Figure S11 reports the amperometric i-t trace and observed product distribution for a control CpI carbon paper electrode that was prepared under oxic conditions in order to render the enzyme inactive; significantly diminished catalytic currents (x20 fold) and products (x17 fold) were observed, consistent with active CpI being necessary for the observed production of H2, HD and D2.…”

Dynamic Equilibrium Model for Surface Nanobubbles in Electrochemistry

“…Numerous bubbles derived from aggregation and nucleation of gas species will occupy the catalytic site and passivate the electrode surface, leading to a lower energy conversion efficiency. Due to the wide research and application of nanoparticles, clusters, or even single atoms as the catalyst for gas-evolving chemical processes, the investigation of gas nanobubbles at the nanocatalyst surface, especially concerning their formation, growth, and detachment, has attracted tremendously increasing attention. − Recently, nanoelectrodes have been developed as a unique tool that enables one to quantitatively investigate individual gas nanobubbles. − From the steady state mass (gas solute or precursor) transport at the disk nanoelectrode, critical gas concentrations corresponding to bubble nucleation for different gas species (H 2 , − N 2 , O 2 , CO 2 , and D 2 ) have been established . More interestingly, high temporal resolution electrochemical responses provided valuable insight into the bubble nucleation rate, , lifetime, and dynamic stability. , Despite the above significant advancements, due to the lack of direct visualization of electrogenerated nanobubbles at nanoelectrodes with feasible spatial and temporal resolution, − further deeper understanding of the gas nanobubble at the electrode surface becomes very challenging.…”

Recent progress in gas nanobubble electrochemistry

“…多种电催化产气反应体系, 并观测到了单个O 2 [29,30] 、 N 2 [31] 、CO 2 [32] 和D 2 [33] . 尽管循环伏安法在单纳米气泡成核研究中可以给 出丰富的稳态传质和电极反应动力学信息 [36] , 但在时 German等人 [37,38] 设计了一种电流阶跃法, 得以在恒定 [39] ; (b) 对应于单个H 2 气泡电化学成核的循环伏安曲线; (c) 不同尺寸Pt纳米电极表面H 2 气泡电化学行为的循环伏安曲线 [28] ; (d) Pt纳米电极上不同气体(H 2 、O 2 、N 2 、CO 2 、D 2 )纳米 气泡电化学成核电流(i p nb )与电极半径(a)的依赖关系; (e) 不同金属(Pt, Au, Pd)纳米圆盘电极上H 2 纳米气泡成核电流与电极半径 的依赖关系 [35] ; (f) 恒流法测定单纳米气泡成核诱导时间 [37] ; (g) 不同恒电流下纳米气泡成核诱导时间与累积概率分布图; (h) 来自循环伏安曲线的气泡成核电流的分布函数及理论预期对比 [39] (网络版彩图) 对于半径介于10至100 nm的球形气泡, 其寿命时 间介于1至100 μs.…”