Department of Chemistry, Clemson University , Clemson, South Carolina 29634, United States.
Department of Chemistry, Texas Tech University , Lubbock, Texas 79409, United States.
J Am Chem Soc. 2018 Feb 7;140(5):1743-1752. doi: 10.1021/jacs.7b10853. Epub 2018 Jan 27.
Ion current densities near 1 A cm at modest bias voltages (<200 mV) are reported for proton and deuteron transmission across single-layer graphene in polyelectrolyte-membrane (PEM)-style hydrogen pump cells. The graphene is sandwiched between two Nafion membranes and covers the entire area between two platinum-carbon electrodes, such that proton transfer is forced to occur through the graphene layer. Raman spectroscopy confirms that buried graphene layers are single-layer and relatively free of defects following the hot-press procedure used to make the sandwich structures. Area-normalized ion conductance values of approximately 29 and 2.1 S cm are obtained for proton and deuteron transport, respectively, through single-layer graphene, following correction for contributions to series resistance from Nafion resistance, contact resistance, etc. These ion conductance values are several hundred to several thousand times larger than in previous reports on similar phenomena. A ratio of proton to deuteron conductance of 14 to 1 is obtained, in good agreement with but slightly larger than those in prior reports on related cells. Potassium ion transfer rates were also measured and are attenuated by a factor of many thousands by graphene, whereas proton transfer is attenuated by graphene by only a small amount. Rates for hydrogen and deuterium ion exchange across graphene were analyzed using a model whereby each hexagonal graphene hollow site is assumed to transmit ions with a specific per-site ion-transfer self-exchange rate constant. Rate constant values of approximately 2500 s for proton transfer and 180 s for deuteron transfer per site through graphene are reported.
在质子和氘通过聚电解质膜（PEM）式氢泵电池中的单层石墨烯传输时，在适度的偏压（<200 mV）下，报告了接近 1 A cm 的离子电流密度。石墨烯夹在两个 Nafion 膜之间，并覆盖两个铂碳电极之间的整个区域，从而迫使质子通过石墨烯层进行转移。拉曼光谱证实，在用于制造三明治结构的热压程序之后，埋入的石墨烯层是单层且相对无缺陷的。通过对 Nafion 电阻、接触电阻等串联电阻的贡献进行校正，得到了通过单层石墨烯的质子和氘传输的面积归一化离子电导率值，分别约为 29 和 2.1 S cm。这些离子电导率值比以前关于类似现象的报告高几百到几千倍。得到的质子与氘离子电导率比为 14 比 1，与之前关于相关电池的报告非常吻合，但略高一些。还测量了钾离子的转移速率，石墨烯使其衰减了数千倍，而质子的转移仅被石墨烯衰减了少量。通过一个模型分析了氢和氘离子在石墨烯上的交换速率，假设每个六方石墨烯的空穴位点都可以用特定的每个位点的离子转移自交换速率常数来传输离子。报告了通过石墨烯的质子转移的约 2500 s 的速率常数值和氘转移的约 180 s 的速率常数值。
