Rospendowiski Júlia, Pinto Maria R, Hessel Cristian, Sitta Elton, Nagao Raphael
Institute of Chemistry, University of Campinas, CEP 13083-970 Campinas, Sao Paulo, Brazil.
Department of Chemistry, Federal University of Sao Carlos, CEP 13565-905 Sao Carlos, Sao Paulo, Brazil.
ACS Omega. 2018 Oct 19;3(10):13636-13646. doi: 10.1021/acsomega.8b02353. eCollection 2018 Oct 31.
We report herein a precise control of the electrochemical bistability induced by surface area changes during the cathodic deposition of copper. Small additions of 1,10-phenanthroline (Phen) in the reaction media present an inhibiting effect on the global rate mainly due to the adsorption of protonated Phen. The increase of its concentration favors a shrinkage of the bifurcation (saddle-node) diagram and shifts it to less negative potentials. The dynamic instability is verified by impedance measurements, and a negative impedance is clearly found. We calculated the apparent molar mass of the adsorbents using in situ gravimetric monitoring in the electrochemical experiments, and the results indicate that mass changes occur mainly due to the reduction of copper from bivalent ions dissolved in the reaction media. Importantly, the adsorption of protonated Phen molecules does not show a considerable contribution in mass variations but prevents the formation of a copper course grained morphology over the surface. Imaging analysis indicates finer nodulations at the lower branch compared to the upper branch in the bistability domain. On the basis of these observations, a kinetic mechanism is proposed and a good agreement is obtained between the apparent molar mass extracted from experiments and the theoretical values. Altogether, our results contribute to a detailed physical chemical description of the nonlinear behavior, bringing new insights about this reaction and pointing out the possibility to design switchable surface electrodes by taking advantage of the bistable behavior.
我们在此报告了在铜的阴极沉积过程中，由表面积变化引起的电化学双稳性的精确控制。反应介质中少量添加1,10 - 菲咯啉（Phen）对整体反应速率具有抑制作用，这主要归因于质子化Phen的吸附。其浓度的增加有利于分岔（鞍结）图的收缩，并将其移向更正的负电位。通过阻抗测量验证了动态不稳定性，并且清楚地发现了负阻抗。我们在电化学实验中使用原位重量监测计算了吸附剂的表观摩尔质量，结果表明质量变化主要是由于反应介质中溶解的二价铜离子的还原。重要的是，质子化Phen分子的吸附在质量变化中没有显示出显著贡献，但阻止了表面上形成粗大晶粒的铜形态。成像分析表明，在双稳性区域中，与上分支相比，下分支处的结节更细。基于这些观察结果，提出了一种动力学机制，并且从实验中提取的表观摩尔质量与理论值之间取得了良好的一致性。总之，我们的结果有助于对非线性行为进行详细的物理化学描述，为该反应带来新的见解，并指出利用双稳性行为设计可切换表面电极的可能性。
