[论文解读] Cobalt-based Co$_3$Mo3N/Co$_4$N/Co Metallic Heterostructure as a Highly Active Electrocatalyst for Alkaline Overall Water Splitting

Yuanwu Liu, Lirong Wang+7 more|arXiv (Cornell University)|Apr 17, 2024

Ammonia Synthesis and Nitrogen Reduction被引用 19

一句话总结

本文报道了一种基于钴的金属异质结构（Co$_3$Mo$_3$N/Co$_4$N/Co/Co）作为高效、耐用的碱性水分解催化剂，实现低电池电压和长期稳定性。

ABSTRACT

Alkaline water electrolysis is considered a commercially viable option for large-scale hydrogen production. However, this process still faces challenges due to the high voltage (>1.65 V at 10 mA cm$^{-2}$) and its limited stability at higher current densities due to the inefficient electron transport kinetics. Herein, a novel cobalt based metallic heterostructure (Co$_3$Mo3N/Co$_4$N/Co/Co) is designed for application for water electrolysis. Operando Raman experiments reveal that the formation of Co$_3$Mo3N/Co$_4$N/Co heterointerface boosts the free water adsorption and dissociation, resulting in a surplus of protons available for subsequent hydrogen production. Furthermore, the altered electronic structure of Co$_3$Mo3N/Co$_4$N/Co heterointerface optimizes the ΔGH of nitrogen atoms at the interface. This synergistic effect between interfacial nitrogen atoms and metal phase cobalt creates highly efficient hydrogen evolution reaction (HER) active sites, thereby enhancing the overall performance. Additionally, the heterostructure exhibits a rapid OH- adsorption rate, coupled with a strong adsorption strength, leading to improved oxygen evolution reaction (OER) performance. Crucially, the metallic heterojunction facilitates fast electron transport, expediting the aforementioned reaction steps and ultimately improving the overall efficiency of water splitting. The water electrolyzer with Co$_3$Mo3N/Co$_4$N/Co/Co as a catalyst exhibits outstanding performance, requiring an impressively low cell voltage of 1.58 V at 10 mA cm$^{-2}$ and maintaining approximately 100% retention over a remarkable 100 h duration at 200 mA cm$^{-2}$. This performance significantly exceeds that of the commercial Pt/C || RuO2 electrolyzer.

研究动机与目标

• 推动用于碱性水电解的高性能、可扩展催化剂。
• 设计并评估基于钴的金属异质结构以提升 HER 和 OER 动力学。
• 阐明提升水分子吸附、氮相关电子结构与电子传输的界面效应。
• 在工业相关条件下的水电解器中展示实际电催化性能。

提出的方法

• 合成 Co$_3$Mo$_3$N/Co$_4$N/Co/Co 金属异质结构。
• 原位拉曼光谱用于监测界面形成和水的吸附/解离。
• 对异质界面的电子结构及其对氮原子 ΔGH 的影响进行分析。
• 评估 OH$^-$ 吸附动力学及 HER 和 OER 的整体催化动力学。
• 电输运研究以将异质结与水分解过程中的快速电子传输联系起来。

实验结果

研究问题

• RQ1 Can the Co$_3$Mo$_3$N/Co$_4$N/Co/Co heterostructure lower the cell voltage for alkaline overall water splitting?
• RQ2 How does the interfacial Co–N environment influence hydrogen evolution and oxygen evolution activity?
• RQ3 What role does fast electron transport at the metallic heterojunction play in overall electrolysis performance?
• RQ4 What is the stability of the catalyst under prolonged operation at high current densities?

主要发现

• The electrolyzer with the Co$_3$Mo$_3$N/Co$_4$N/Co/Co catalyst requires 1.58 V at 10 mA cm$^{-2}$.
• The catalyst maintains ~100% retention over 100 h at 200 mA cm$^{-2}$.
• Operando Raman shows interfacial Co$_3$Mo$_3$N/Co$_4$N/Co formation boosts water adsorption and dissociation.
• Interfacial nitrogen atom–metal interactions optimize ΔGH and enhance HER activity.
• The heterostructure exhibits rapid OH$^-$ adsorption with strong adsorption strength, improving OER performance.
• Fast electron transport across the metallic junction accelerates the overall water-splitting process.