Solar Hydrogen Evolution through Ammonia Oxidation using Hybrid Ruthenium-based Electroanodes
Anna M Beiler a, Alisa Denisiuk a, Wenhui Li a, Jan Holub a, Francisco-Javier Sánchez-Baygual a, Marcos Gil-Sepulcre a, Mehmed Z. Ertem b, Dooshaye Moonshiram c, Alberto Piccioni d, Emilio Palomares a f, Antoni Llobet a e
a Institute of Chemical Research of Catalonia (ICIQ), Avinguda Països Catalans 16, Tarragona 43007
b Brookhaven National Laboratory, Chemistry Department, Upton, NY, USA, 11973, United States
c Institute of Materials Science of Madrid (ICMM-CSIC), Calle Sor Juana Inés de la Cruz, 3, Madrid, Spain
d Department of Physics and Astronomy, University of Bologna
e Departament de Química, Universitat Autònoma de Barcelona, UAB, Cerdanyola del Vallès, Spain
f Catalan Institution for Research and Advanced Studies (ICREA) Passeig Lluïs Companys, 23, 08010, Barcelona, Spain
Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS23 & Sustainable Technology Forum València (STECH23) (MATSUS23)
#e-FuelSyn - Electrocatalysis for the Production of Fuels and Chemicals
VALÈNCIA, Spain, 2023 March 6th - 10th
Organizers: Carla Casadevall Serrano and Julio Lloret Fillol
Poster, Anna M Beiler, 366
Publication date: 22nd December 2022

Molecular catalysts can catalyze ammonia oxidation, providing insights into the electrochemical N2 cycle for a carbon-free fuel economy. We investigate the ammonia oxidation activity of hybrid carbon anodes functionalized with the oligomer {[RuII(bda-κ-N2O2)(4,4′-bpy)]10(4,4′-bpy)} (where bda = [2,2′-bipyridine]-6,6′-dicarboxylate and 4,4′-bpy is 4,4′-bipyridine; Rubda-10). Electrocatalytic studies in propylene carbonate demonstrate that the Ru-based hybrid electrode transforms NH3 to N2 and H2 with 100% FE at an applied potential of 0.05 V vs Fc+/0, with a TON of up to 7500. The catalytic wave onset (defined as the potential required to reach 0.1 mA cm-2) is -0.04 V vs Fc+/0. XAS analysis after bulk electrolysis confirms the molecular integrity of the catalyst. The state-of-the-art stability is attributed to the immobilization of the catalyst that may shut down some decomposition pathways. We propose that nucleophilic attack by NH3 is the primary catalytic mechanism, given that the bimolecular pathway is disfavored through the immobilization of the catalyst. Given the lower thermodynamic requirements of ammonia oxidation compared to water oxidation, we show that a single perovskite solar cell with an open-circuit potential of 1.08 V can power the electrochemical generation of hydrogen. This is in contrast to obtaining solar-powered H2 fuel from water splitting, which typically requires multiple photovoltaic cells and/or junctions to drive the reaction. This research illustrates the potential for immobilized molecular catalysts to facilitate ammonia oxidation, a crucial consideration in direct ammonia fuel cell design.

Financial support from Ministerio de Ciencia e Innovación through Projects PID2019-111617RB-I00 (MCIN/AEI/10.13039/501100011033) and SO-CEX2019-000925-S (MCIN/AEI/10.13039/5011000110) is gratefully acknowledged. This project has received funding from the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 754510-PROBIST (J.H.). This work was supported by Marie Skłodowska-Curie Actions Individual Fellowship grant funding to A.M.B., Grant 101031365-SolTIME. D.M. acknowledges support from a Spanish Ministerio de Ciencia, Innovacion y Universidades, grant (PID2019-111086RA-I00), a PIE grant from CSIC-ICMM (20226AT001), and the Ramon y Cajal Fellowship (RYC2020-029863-I). The work at Brookhaven National Laboratory (M.Z.E.) was carried out under contract DE-SC0012704 with the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, and utilized computational resources at the Center for Functional Nanomaterials, which is a U.S. Department of Energy Office of Science Facility, and the Scientific Data and Computing Center, a component of the Computational Science Initiative, at Brookhaven National Laboratory under Contract No. DE-SC0012704.

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