TY - JOUR A1 - Zhang, Wuyi A1 - Mehmood, Asad A1 - Ali, Ghulam A1 - Liu, Hui A1 - Chai, Liyuan A1 - Wu, Jun A1 - Liu, Min T1 - Nickel Nanocluster-Stabilized Unsaturated Ni–N3 Atomic Sites for Efficient CO2-to-CO Electrolysis at Industrial-Level Current N2 - Unsaturated Ni single-atom catalysts (SACs), Ni-Nx (x=1,2,3), have been investigated to break the conventional Ni-N4 structural limitation and provide more unoccupied 3d orbitals for CO2 reduction reaction (CO2RR) intermediates adsorption, but their intrinsically low structural stability has seriously hindered their applications. Here, we developed a strategy by integrating Ni nanoclusters to stabilize unsaturated Ni-N3 atomic sites for efficient CO2 electroreduction to CO at industrial-level current. Density Functional Theory (DFT) calculations revealed that the incorporation of Ni nanocluster effectively stabilizes the unsaturated Ni-N3 atomic sites and modulates their electronic structure to enhance the adsorption of the key intermediate *COOH during CO2RR. Guided by these insights, we prepared an optimal composite catalyst, Ni6@Ni-N3, which features a Ni6N6 nanocluster surrounded by six Ni-N3 single atoms sites, through low-temperature pyrolysis. The morphology and coordinative structure of Ni6@Ni-N3 were confirmed by an aberration-corrected transmission electron microscope (AC-TEM) and X-ray absorption spectroscopy (XAS). As a result, Ni6@Ni-N3 demonstrated a remarkably high CO Faradaic efficiency (FECO) of 99.7 % and a turnover frequency (TOF) of 83984.2 h−1 at 500 mA cm−2 under −1.15 VRHE, much better than those of Ni-N4 with a lower FECO of 86 % at 100 mA cm−2 and a TOF of 39309.9 h−1under identical potential. XAS analyses of Ni6@Ni-N3 before and after long-term CO2RR testing confirmed the excellent stability of its coordinative environment. This work highlights a generalizable approach for stabilizing unsaturated single-atom catalysts, paving the way for their application in high-performance CO2RR. KW - Electrochemical CO2 conversion KW - Single atom catalysts KW - CO2 electrolysis PY - 2025 DO - https://doi.org/10.1002/anie.202424552 SN - 1521-3773 VL - 64 IS - 13 SP - 1 EP - 10 PB - Wiley-VCH CY - Weinheim AN - OPUS4-62926 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Mehmood, Asad T1 - Atomically Coordinated Non-Precious Metal Electrocatalysts Using Active Site Imprinted Carbon Matrix N2 - Non-precious metal catalysts generally represented as M-N-C (where M= Fe, Co, Ni etc.) have shown encouraging activity levels for different electrochemical applications involving oxygen reduction reaction (ORR) and carbon dioxide reduction reaction (CO2RR). High activities of these electrocatalysts mainly come from transition metal centres that are atomically dispersed as M-N4 active sites within a nitrogen doped carbon matrix. Because of the required pyrolytic synthesis conditions, it is quite challenging to prepare M-N-Cs that purely consist of M-N4 active sites. Classical synthesis routes often result in the formation of additional side phases such metallic nanoparticles or metal carbides, which limit the density of M-N4 sites and lead to lower catalytic activity.1 Herein, we present our work on M-N-C synthesis using an active site imprinting approach as an alternate synthetic route to address the above-mentioned issue. We show that both Mg and Zn can be used for active site imprinting. The imprinted coordination environment can be coordinated with various transition metal ions, resulting in Fe-N-C, Co-N-C and Ni-N-C catalysts containing M-N4 sites exclusively.2-4 The electrochemical performance of the synthesized catalysts is evaluated for CO2RR and ORR. Ni-N-Cs exhibit an excellent CO2 reduction activity with high CO faradic efficiency value of 95% at U= -0.5 to -0.8 VRHE (vs reversible hydrogen electrode) and a mass activity of 23 A g-1. The performance stability test carried out at -0.65 VRHE demonstrates above 92 % retention of the current density and 97 % retention of the CO selectivity after 100 h of continuous operation, reflecting the structural robustness of the Ni-N-C catalyst in CO2RR test environment. When employed as ORR catalysts, both Fe-N-C and Co-N-C deliver promising activities with half-wave potentials >0.8 VRHE in acidic electrolyte and >0.9 VRHE in alkaline electrolyte. The talk will include greater details of the structural analysis and electrochemical performance evaluation of these catalysts. T2 - 73rd Annual Meeting of the International Society of Electrochemistry CY - Online meeting DA - 12.09.2022 KW - Non-precious metal catalysts KW - Single atom catalysts KW - Electrochemical CO2 conversion PY - 2022 AN - OPUS4-61986 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Mehmood, Asad A1 - Fellinger, Tim-Patrick T1 - Porous Carbon Supported Ni and Co Single Atom Catalysts for Electrochemical Reduction of Carbon Dioxide N2 - Non-precious metal single atom catalysts (generally labelled as M/NCs where M= Co, Fe, Ni etc.) consist of active metal centres dispersed on nitrogen doped porous carbon (NC) matrix at atomic level and exhibit promising activities e. g. for electrochemical reduction of CO2, selectively forming CO. We herein use identical Mg/NCs as platform for ion-exchange reactions towards morphologically equivalent Ni/NCs and Co/NCs. The Ni/NC catalyst shows almost double the specific activity and a Faraday efficiency of >80% at a very low overpotential of U= -0.43 V (even 95% at U= -0.5 to -0.8 V) with high stability. T2 - GDCh Electrochemistry 2022 CY - Berlin, Germany DA - 27.09.2022 KW - Electrochemical CO2 conversion KW - Single atom catalysts KW - Porous Carbons PY - 2022 AN - OPUS4-61980 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pedersen, Angus T1 - Coupling Single Atom Electrocatalysts with a Bioreactor for CO2 to C2+ Conversion N2 - To alleviate CO2 emissions impact on climate change, and close the carbon cycle, converting carbon dioxide into valuable products such as multi-carbon organic chemicals is of great importance. Each approach offers distinct merits but also certain challenges in terms of process efficiency, product selectivity and implementation at scale. Developing coupled CO2 conversion systems, for instance bio-electrochemical reactors, can address some of the challenges.[1] Precious-metal free biocompatible single atoms in N-doped C (M-N-C, where M = Fe, Ni, Co) electrocatalysts, based on Mg active site imprinting of bioinspired MN4 sites,[2][3] have shown state-of-the-art activity and selectivity for conversion of CO2 to CO.[4] Pyrolysis of Mg-N-C is carried out in a salt-melt at high temperatures (≥ 800 oC) and followed by an exchange with stoichiometric amounts of Ni or Co at low temperatures. N2-sorption of the materials reveal a micro-mesoporous structure with high surface areas (> 1000 m2 g-1) and a mass-transport enabling pore system. Extended X-ray absorption fine structure reveal the existence of atomically dispersed single atom active sites with defined active site structure. These catalysts were implemented in a home-made bio-electrocatalytic system (BES) consisting of a bioreactor coupled to a CO2 electrolysis cell.[5] Here, CO2 is first electrochemically converted to CO in the electrolysis cell which is then directly fed to bacteria (Clostridium ragsdalei) in the bioreactor which further metabolize it to valuable carbon compounds, such as acetate. An acetate formation rate of 1.8 mg L-1 h-1 was achieved and an acetate concentration of 0.103 g L-1, corresponding to acetate formation rate of 0.73 mmol d-1. We have successfully demonstrated the validity of a coupled bio-electrocatalytic system operating with resource efficient single atom Co- and Ni-N-C electrocatalysts for CO2 conversion. T2 - Electrifying Organic Synthesis CY - Mülheim an der Ruhr, Germany DA - 03.09.2025 KW - Single atom KW - Electrochemical CO2 conversion KW - Bioelectrolysis PY - 2025 AN - OPUS4-64037 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -