【摘要】 质子交换膜燃料电池（PEMFC）正极产生的水如不能及时排除,大量的积水将淹没催化层,使得氧气不能进入催化层得到电子还原为氢氧根,取而代之的是氢离子得到电子被还原为氢气,使正极电位低于负极电位（无论负极是氢还是甲醇的氧化）,从而使单电池的输出电压为负,对整个电池组产生“负差效应”。针对这种情况,在传统正极催化剂Pt/C中添加了MnO₂制成MnO₂-Pt/C复合电极,希望在缺氧的时候与氧还原反应（ORR）有着相近电位的MnO₂能吸收来自外电路的电子,完成正极上的还原反应,消除负差效应。通过用N₂和O₂分别饱和的1 mol·L^-1H₂SO₄来模拟缺氧和富氧情况下的MnO₂-Pt/C和Pt/C电极的电化学性能,证实含有MnO₂的MnO₂-Pt/C复合电极对PEMFC由于正极缺氧所导致的负差效应有抑制作用;在PEMFC中采用MnO₂-Pt/C正极复合电极,在缺氧的情形下,即N₂饱和的1 mol·L^-1H₂SO₄中,负载1mg Pt·cm^-2的Pt/C电极电流趋于0,而负载0.5 mg Pt·cm^-2和2.5 mg MnO₂·cm^-2的MnO₂-Pt/C复合电极借助MnO₂自身的电化学还原反应,能够维持0.35 mA·cm^-2稳定的还原电流,从而避免了Pt/C正极抑制因质子H⁺还原所造成的正极电位下降;在富氧的情形下,MnO₂不仅不影响Pt对ORR的催化效果,而且还有协同催化ORR的作用。为克服质子交换膜燃料电池因正极积水、缺氧而导致的负差效应,提供了一种化学的解决方案。更多还原

【Abstract】 Water is always produced at the cathode of polymer electrolyte membrane fuel cells（PEMFC）.If water were not removed timely, it would accumulate at the cathode of PEMFC and further flood the cathode. With water accumulation and the cathode flooded, oxygen starvation, and even oxygen depletion would occur at the cathode. In this case, protons H⁺ reduction reaction （PRR） carries on at the cathode of PEMFC rather than oxygen reduction reaction（ORR）. It would cause a remarkable decline of cathode potential as ORR was replaced by PRR. The output voltage of a single cell with oxygen starvation would be likely reversed. This phenomenon was defined as voltage reversal effect in this paper. Aiming at solving the so-called voltage reversal effect, a MnO₂-Pt/C composite electrode was proposed to replace the conventional Pt/C electrode. The electrochemical reduction of MnO₂ in the composite electrode, which has "almost the same Nernst potential as ORR, would be served as a substitute for ORR in the case of oxygen starvation. Therefore, the voltage reversal effect caused by PRR could be avoided at the cathode. Two environments, N₂-saturated H₂SO₄ and O₂-saturated H₂SO₄, were adopted to simulate the two situations,i. e.,O₂ starvation and O₂ riches. It has been found that MnO₂-Pt/C can restrain the voltage reversal effect to a certain extent. In a N₂-saturated 1 mol· L^-1 H₂SO₄, the current density on a Pt/C electrode with 1 mg Pt·cm^-2 was close to 0, but this value on a MnO₂-Pt/C composite electrode with 0.5 mg Pt·cm^-2 as well as 2.5 mg MnO₂·cm^-2 was 0.35 mA·cm^-2. In a O₂-saturated 1 mol ·L^-1 H₂SO₄, the presence of MnO₂ in a MnO₂-Pt/C composite electrode primarily plays a role of assistant catalysts for ORR. It enhances the catalytic ability of Pt to ORR. The mechanism of MnO₂ catalyzing ORR was discussed in the case of oxygen riches plus the presence of Pt at the end of this paper. It has demonstrated that the MnO₂-Pt/C composite electrode opens a new way to overcoming the voltage reversal effect of PEMFC in the case of oxygen starvation.更多还原