Devi Hemam Rachna, Nandan Ravi, Nanda Karuna Kar
Materials Research Centre, Indian Institute of Science, Bangalore 560012, India.
ACS Appl Mater Interfaces. 2020 Mar 25;12(12):13888-13895. doi: 10.1021/acsami.9b22956. Epub 2020 Mar 16.
Oxides are envisioned as promising catalysts to facilitate water oxidation, and the benign presence of hydroxide moieties can further enhance the catalyst performance. However, the nature of synergy between oxides and hydroxides remains elusive. In this study, we have designed a one-pot solution growth technique for the synthesis of flower-shaped N-doped-C-enveloped NiCoO/NiCo(OH) catalysts with varying oxide and hydroxide contents and investigated their water oxidation behavior. The correlation between performance-determining parameters involved in water oxidation, such as the onset potential and overpotential with oxide and/or hydroxide content, oxidation states (oxides), and elemental composition (Co/Ni content), and the possible ways to achieve their optimal values are discussed in detail. Our observations conclude that the onset potential and overpotential are minimal for the hybrid oxide-hydroxide bimetallic system compared with pristine hydroxide or oxide. The optimal hybrid catalyst shows excellent current density, low Tafel slope (82 mV/dec), and low onset potential (281 mV at 2 mA/cm) and overpotential (348 mV at 10 mA/cm), besides enduring operational stability in alkaline medium. The low Tafel slope suggests the preferable kinetics for water oxidation, and the poisoning study reveals the direct involvement of metal as active sites. The overall study unveils the synergy in the Co-Ni-based binary transition-metal oxide-hydroxide hybrid, which makes it a potential candidate for water oxidation catalysts, and hence, it is expected that the hybrid will find applications in energy conversion devices, such as electrolyzers.
氧化物被视为促进水氧化的有前景的催化剂，氢氧化物部分的良性存在可进一步提高催化剂性能。然而，氧化物和氢氧化物之间协同作用的本质仍然难以捉摸。在本研究中，我们设计了一种一锅法溶液生长技术，用于合成具有不同氧化物和氢氧化物含量的花状氮掺杂碳包覆的NiCoO/NiCo(OH)催化剂，并研究了它们的水氧化行为。详细讨论了水氧化过程中涉及的性能决定参数之间的相关性，如起始电位和过电位与氧化物和/或氢氧化物含量、氧化态（氧化物）和元素组成（钴/镍含量），以及实现其最佳值的可能方法。我们的观察结果表明，与原始氢氧化物或氧化物相比，混合氧化物-氢氧化物双金属体系的起始电位和过电位最小。除了在碱性介质中具有持久的操作稳定性外，最佳混合催化剂还表现出优异的电流密度、低塔菲尔斜率（82 mV/dec）、低起始电位（在2 mA/cm时为281 mV）和过电位（在10 mA/cm时为348 mV）。低塔菲尔斜率表明水氧化具有较好的动力学，中毒研究揭示了金属作为活性位点的直接参与。总体研究揭示了钴-镍基二元过渡金属氧化物-氢氧化物混合物中的协同作用，这使其成为水氧化催化剂的潜在候选者，因此，预计该混合物将在能量转换装置如电解槽中得到应用。
