Wang Yuzhen, Dutta Abhijit, Iarchuk Anna, Sun Changzhe, Vesztergom Soma, Broekmann Peter
Department of Chemistry, Biochemistry and Pharmaceutical Science, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.
State Key Laboratory of Eco-Hydraulics in Northwest Arid Region of China, Xi'an University of Technology, No.5 South Jinhua Road, Xi'an, Shaanxi 710048, China.
ACS Catal. 2023 Jun 5;13(12):8169-8182. doi: 10.1021/acscatal.3c00716. eCollection 2023 Jun 16.
The hydrogen evolution reaction (HER) is often considered parasitic to numerous cathodic electro-transformations of high technological interest, including but not limited to metal plating (e.g., for semiconductor processing), the CO reduction reaction (CORR), the dinitrogen → ammonia conversion (NRR), and the nitrate reduction reaction (NORR). Herein, we introduce a porous Cu foam material electrodeposited onto a mesh support through the dynamic hydrogen bubble template method as an efficient catalyst for electrochemical nitrate → ammonia conversion. To take advantage of the intrinsically high surface area of this spongy foam material, effective mass transport of the nitrate reactants from the bulk electrolyte solution into its three-dimensional porous structure is critical. At high reaction rates, NORR becomes, however, readily mass transport limited because of the slow nitrate diffusion into the three-dimensional porous catalyst. Herein, we demonstrate that the gas-evolving HER can mitigate the depletion of reactants inside the 3D foam catalyst through opening an additional convective nitrate mass transport pathway provided the NORR becomes already mass transport limited prior to the HER onset. This pathway is achieved through the formation and release of hydrogen bubbles facilitating electrolyte replenishment inside the foam during water/nitrate co-electrolysis. This HER-mediated transport effect "boosts" the effective limiting current of nitrate reduction, as evidenced by potentiostatic electrolyses combined with an operando video inspection of the Cu-foam@mesh catalysts under operating NORR conditions. Depending on the solution pH and the nitrate concentration, NORR partial current densities beyond 1 A cm were achieved.
析氢反应（HER）通常被认为是许多具有高科技价值的阴极电转化过程中的寄生反应，包括但不限于金属电镀（例如用于半导体加工）、CO还原反应（CORR）、二氮→氨转化反应（NRR）以及硝酸盐还原反应（NORR）。在此，我们介绍一种通过动态氢气泡模板法电沉积在网状载体上的多孔泡沫铜材料，作为电化学硝酸盐→氨转化的高效催化剂。为了利用这种海绵状泡沫材料固有的高表面积，将硝酸盐反应物从本体电解质溶液有效地传输到其三维多孔结构中至关重要。然而，在高反应速率下，由于硝酸盐向三维多孔催化剂中的扩散缓慢，NORR很容易受到传质限制。在此，我们证明，只要NORR在HER开始之前已经受到传质限制，析氢反应就可以通过开辟一条额外的对流硝酸盐传质途径来减轻三维泡沫催化剂内部反应物的消耗。这条途径是通过在水/硝酸盐共电解过程中形成并释放氢气泡来促进泡沫内部的电解质补充而实现的。这种HER介导的传输效应“提高”了硝酸盐还原的有效极限电流，恒电位电解结合在NORR操作条件下对泡沫铜@网状催化剂的原位视频观察证明了这一点。根据溶液pH值和硝酸盐浓度，实现了超过1 A cm的NORR分电流密度。
