To solve the key problems of current electrocatalytic oxidation synthesis methods for H2O2,such as poor catalytic performance of electrode materials,boron-doped diamond (BDD) electrode materials with controlled boron doping levels and sp2/sp3 carbon content ratios are prepared via a hot filament chemical vapor deposition (HFCVD) technology.This study investigates systematically the impacts of the BDD preparation process on the performance of BDD electrode in catalyzing the 2-electron water oxidation reaction (2e--WOR) for H2O2 generation,ultimately obtaining the electrode material with excellent performance and optimizing the preparation process.Study reveals that boron doping concentration plays a decisive role.The variation in boron doping concentration in BDD electrode affects significantly the selectivity and generation rate of H2O2 over BDD electrode catalysis.BDD electrode with a boron-to-carbon ratio of 0.9% can ensure both good film-forming quality and excellent catalytic performance,delivering a Faraday efficiency of 61.9%,and a H2O2 production rate of 72.7 μmol/(cm2·min) at a current density as high as 500 mA/cm2.Additionally,under the same boron doping concentration,the lower the ratio of sp2/sp3 carbon in the BDD electrode,the more favorable it is for the selective generation of H2O2.These findings demonstrate that a superior selectivity will be demonstrated when BDD electrode with an appropriate boron doping concentration and low sp2 carbon content is served in electrocatalytic oxidation synthesis methods for H2O2.Such a BDD electrode can deliver a higher H2O2 generation speed under high current density.This work highlights the potential of BDD electrodes as high-performance catalysts for electrocatalytic synthesis of hydrogen peroxide.
由不同硼掺量BDD电极电催化氧化合成H2O2的法拉第效率(FE)和生成速率随电位变化关系如图3(a)、(b)所示,硼掺量为0.9%的BDD电极在相同电位下展现出比其他BDD电极更高的FE和H2O2生成速率,其FE值最高可达61.9%,而在3.48 V vs.RHE时最大H2O2生成速率为72.7 μmol/(cm2·min)。随着硼掺量的增加,BDD薄膜逐渐展现出金属性质,从而提高其电导率并降低过电势。但硼掺量达到一定水平(0.9%)后,继续增加会导致sp2石墨相碳含量的增加,这可能会促进四电子水氧化反应(4e--WOR,起始电位为1.23 V vs.RHE)而抑制两电子水氧化反应(2e--WOR,起始电位为1.67 V vs.RHE)。图3(c)展示了不同电流密度下各电极催化性能测试结果。结果显示,随着电流密度的增加,H2O2生成速率也随之增加,在电流密度低于300 mA/cm2时,H2O2生成速率与电流密度之间呈现出近似线性关系。当电流密度超过300 mA/cm2后,尽管H2O2生产量仍在增加,但增长速率开始减缓。这表明在本实验条件下,300 mA/cm2是最佳的电流密度,且在此电流密度下BDD薄膜能够稳定运行。
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