Exploiting Multifunctionality of M2+ (M=Co2+, Ni2+) Phosphides for Electrocatalysis toward HER, OER and ORR

INTRODUCTION The scarcity and high cost of Pt and Ru/Ir-based noble metal electrocatalysts forces to design alternative low-cost and efficient materials for sustainable energy storage and conversion technologies1. Among them, phosphorus-containing coordination polymers, such as metal phosphonates and phosphinates, have emerged as potential precursors of transition-metal phosphide (TMP) electrocatalysts2. EXPERIMENTAL STUDY Pyrolysis under 5%H2-Ar atmosphere at different temperatures. Electrocatalytic performances were investigated toward Oxygen Evolution Reaction (OER), Oxygen Reduction Reaction (ORR) and Hydrogen Evolution Reaction (HER). RESULTS AND DISCUSSION In this research-work, we report the synthesis and crystal structure of several families of divalent metal (Co2+, Ni2+) derived from the (2-carboxyethyl)(phenyl)phosphinic acid (CEPPA)3 and etidronic acid4. These solids were used as precursor of metal phosphides (M2P/MP) by thermal reduction under 5%H2-Ar atmosphere at different temperatures and their electrocatalytic performances were investigated toward OER, ORR and HER. The relationship between M/P molar ratios and/or the M2+ coordination environment in the precursor structures and the electrocatalytic activity of the prepared metal phosphides will be discussed. The presence/absence of N-doped carbon graphitic matrix in the final materials will be also studie

Preparation and characterization of phosphorus-containing electrocatalyst for OER, HER and ORR.

Phosphorus-based materials, such as transition metal phosphides and phosphates/pyrophosphates, have drawn considerable attention as promising alternatives to noble metal-based catalysts (Pt, Ru, Ir) owing to their widely tunable electrocatalytic properties. In this work, we propose the preparation of electrocatalysts using metal phosphonates of composition M(O3PCH(OH)COOH)·2H2O (M2+= Mn, Fe, Co, and Ni) as precursors. The electrocatalysts were obtained by pyrolytic treatments (N2 or 5%H2-Ar atmospheres) giving rise to a wide family of crystalline and amorphous metal pyrophosphates and phosphides. The full-characterised solids by XRD (laboratory and synchrotron), TEM and XPS were then assayed as catalysts for Oxygen Evolution Reaction (OER), Oxygen Reduction Reaction (ORR) and Hydrogen Evolution Reaction (HER). The amorphous iron(II)-doped cobalt pyrophosphate and crystalline phosphides (MP and/or M2P; and M2+= Co, Ni) exhibited the best performances and long-times stabilities. On the other hand, pair distribution function (PDF) studies, using synchrotron radiation, and XPS analysis reveal that the amorphous/crystalline phases are stable for the HER and ORR processes, while solids evolve to other active phases, such as (oxy)hydroxides, upon conducting the OER. The performance of selected electrocatalysts has been tested for H2 production and monitored by laboratory X-ray computed nanotomography (nanoCT).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Electrocatalytic properties of spray-drying-synthesized cobalt or nickel phosphonate-derived materials.

As a class of coordination polymers (CPs), metal phosphonates (MPs) are constructed by coordination bonds connecting metal sites and phosphonate (RPO32−) ligands, where the metal sites are dispersed uniformly at the atomic level. This feature facilitates the construction of OER/HER transition metal phosphide (TMP) pre-catalysts, making them very attractive precursors of Non-Precious Metal Electrocatalysts (NPMCs) [1, 2] In this work, we report the synthesis and crystal structures of several transition-metal phosphonates derived from the phosphonopropionic acid (PPA), [FexM1-x(HO3PCH2CH2COO)2(H2O)2; M=Co2+ or Ni2+; x= 0, 0.2]. These solids have been prepared for the first time by spray-drying synthesis directly on carbon paper (CP) (Scheme 1). Pyrolysis of spray-dried materials in 5%-H2/Ar led to TMP-based energy-conversion electrocatalysts. As compared with other conventional procedures, this synthetic methodology allowed to improve the water-splitting activity.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. PID2019-110249RB-I00/AEI/10.13039/501100011033 TED2021–129836B-I00/AEI/10.13039/501100011033/Uni´on Europea NextGenerationEU/PRTR (MICIU, Spain) P20-00416 (Junta de Andalucia, Spain/FEDER

Using transition metal tetraphosphonates as precursor of phosphorus-containing electrocatalysts

Coordination polymers (CPs) are widely studied due to their applicability in many fields. Among them, metal phosphonates (MPs) are attractive materials due to their versatile structural diversity and functionality, with interesting properties as proton conductors and electrocatalyst precursors. In this work, we report the synthesis and crystal structures of several MPs derived from the combination of hexamethylenediamine-N,N,N’,N’-tetrakis(methylenephosphonic acid) (HDTMP) with different transition metals (M2+= Mn, Fe, Co, and Ni). The resulting solids, M[(HO3PCH2)2N(CH2)6N(CH2PO3H)2]·2H2O, show pillared-layered structures with capabilities of ammonia adsorption (Co2+ and Ni2+ derivatives). The ammonia-containing solids are crystalline, with a composition M[(HO3PCH2)2N(CH2)6N(CH2PO3H)2(H2O)2](NH3)4(H2O)12. The catalytic activities toward Oxygen Evolution Reaction (OER), Oxygen Reduction Reaction (ORR) and Hydrogen Evolution Reaction (HER) of the corresponding (5% H2-Ar)-pyrolyzed materials, as well as the crystal structure of non-pyrolyzed precursor solids, will be discussed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Electrocatalytic properties of cobalt phosphides and pyrophosphates derived from phosphonate-based-MOFs

As a class of coordination polymers (CPs), metal phosphonates (MPs) are constructed by coordination bonds connecting metal sites and phosphonate (RPO32−) ligands, where the metal sites are dispersed uniformly at the atomic level. This feature facilitates the construction of metalphosphorous-based/nano-carbon composites by one-step pyrolysis, making them very attractive precursors of Non-Precious Metal Electrocatalysts (NPMCs) [1, 2] In this work, we report the synthesis, characterization and electrochemical properties of three cobalt(II) coordination polymers erived from the N,N-bis(phosphonomethyl)glycine (BPMGLY), Co(C4H9O8NP2·nH2O (n=2-4). These MPs, with different frameworks according to the crystallographic data, are used as precursors of new NPMCs by pyrolytic treatment under 5%-H2/Ar at different temperatures. The electrochemical behavior of the resulting compounds, mainly crystalline cobalt pyrophosphates and/or phosphides, is fully investigated regarding to the Oxygen Evolution and Reduction Reactions (OER and ORR, respectively) as well as Hydrogen Evolution Reaction (HER). In general, cobalt phosphides (CoP) derived from compound Co-BPMGLY-I (n=4), displayed better performances for the HER with an overpotential of 156 mVUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Cobalt phosphinates as precursors of cobalt phosphide electrocatalysts

https://qies22.icms.us-csic.es/The scarcity and high cost of Pt and Ru/Ir-based noble metal electrocatalysts forces to design alternative low-cost and efficient materials for sustainable energy storage and conversion technologies. Among them, phosphorus-containing coordination polymers, such as phosphinates, have emerged as potential precursors of transition-metal phosphide (TMP) electrocatalysts. The possibility of incorporating two funtionalized organic moieties into the phosphinate ligands makes metal phosphinates highly attractive precursors to obtain core-shell carbon/TMP electrocatalysts. In this research-work, we report the synthesis and crystal structure of two Co2+-phosphinates derived from the (2-carboxyethyl)(phenyl)phosphinic acid (CEPPA), Co2[(O2P(CH2CH2COO)(C6H5)(H2O)]2·2H2O (CoCEPPA-1D) and Co3[O2P(CH2CH2COO)(C6H5)]2(OH)2 (CoCEPPA-2D), synthesized by microwave-assisted method. These solids were used as precursor of cobalt phosphides (Co2P/CoP) by thermal reduction under 5%H2-Ar atmosphere at different temperatures and their electrocatalytic performances were investigated toward Oxygen Evolution Reaction (OER), Oxygen Reduction Reaction (ORR) and Hydrogen Evolution Reaction (HER). The relationship between Co/P molar ratios and/or the Co2+ coordination environment in the precursor structures and the electrocatalytic activity of the prepared cobalt phosphides will be discussed.Proyectos de investigación PID2019-110249RB-I00 (MICIU/AEI, Ministerio de España) y PY20-00416 (Junta de Andalucia, Spain/FEDER). Ayudas para Doctores PAIDI2020 (DOC_00272 Junta de Andalucia, España) y Plan Propio de Investigación de la Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Proton Conduction Properties of Metal phosphonates and Application as Fillers in PEMFCs

Metal phosphonate (MP)-based coordination polymers (CPs) are structurally versatile multifunctional compounds containing different acidic groups such as P-OH; SO3H, COOH, N+-H, etc. These features result in the formation of extended H-bond networks and confer a wide range of proton conduction properties to be used as components of membrane electrode assemblies (MEAs).In this work, the focus is placed on the proton conduction properties of coordination polymers derived from the combination of lanthanide ions with different multifunctional phosphonic ligands, such as phosphonotaurine (2-[bis(phosphonomethyl)amino]-ethanesulfonic acid) or nitrilo-tris (methylenephosphonic acid). High-throughput hydrothermal screening has been used to reach optimal synthesis conditions. Their crystal structures were solved ab initio from X-ray powder or single-crystal diffraction data. Proton conductivities of the MPs and Nafion-mixed membranes were determined by electrochemical impedance spectroscopy (EIS). We report the synthesis and structural features of several members of both families of MPs. The presence of the different functional groups in these ligands such us free sulfonic groups or the incorporating sulphate species into the framework of CPs, lead to a wide variety of metal ligand coordination modes and frameworks, which determine their proton conductivity properties, ranged between 10−3 and 10−2 S·cm−1 at 90 °C and 95% RH. Selected materials were studied as fillers for the preparation of Nafion-mixed membranes, and their responses in proton exchange membrane fuel cells (PEMFCs) were established under operating conditions. The structural role and orientation of the acid groups of the ligand contribute to tune the H-bonding networks and, hence, the proton transfer processes. Preliminary results indicate that these solids perform satisfactorily as fillers of Nafion-based membranes, showing power and current densities higher than those of the pristine Nafion in short times.Esta invetigación fue financiada por los proyectos de investigación PID2019−110249RB-I00 (MICIU/AEI, España) y PY20−00416 (Junta de Andalucía, España/FEDER). M.B.G. agradece la ayuda a los contratatos PAIDI2020 DOC_00272 Junta de Andalucía, España) y R.M.P.C.agradece a la Universidad de Málaga con el Plan Propio de Investigación por la financiación prestada

Synthesis, structural characterization and electrocatalytic properties of cobalt phosphides and pyrophosphates derived from glyphosine

Póster presentado en el XXX Simposio del GE3CMetal phosphonates (MPs), a subclass of coordination polymers, result from the bonding of phosphonic acids (RPO32-) with metal ions, giving rise to an uniformly dispersion of the metal sites at the atomic scale. This characteristic allows the preparation of metal-phosphorous-based nano-carbon composites by a simple one-step pyrolysis, what makes them very attractive precursors of Non-Precious Metal Catalysts (NPMCs). Herein, we report the synthesis, characterization and electrochemical properties of three cobalt(II) coordination polymers derived from the glycine-N,N-bis(methylenenphosphonic acid) (BPMGLY), with formula [Co(C4H9O8NP2(H2O)2]·nH2O (n=0, 2). In contrast with the zero-dimensional structure of [Co(C4H9O8NP2(H2O)2]·2H2O (Co-BPMGLY-I), the two new polymorphs synthesized, Co(C4H9O8NP2(H2O)2 (Co-BPMGLY-II and Co-BPMGLY-III), whose structures have been solved from powder diffraction data, show two-dimensional frameworks with different connectivity between the Co2+ ions and the ligand within the sheets. These MPs were used as precursors of NPMCs by pyrolyzing them under 5%-H2/Ar at different temperatures. The electrochemical behavior of the resulting compounds, mainly crystalline cobalt pyrophosphates and/or phosphides, is fully studied regarding to the Oxygen Evolution and Reduction Reactions (OER and ORR, respectively) as well as Hydrogen Evolution Reaction (HER). Cobalt phosphide (CoP) derived from Co-BPMGLY-I displayed the best results, showing an overpotential of 156 mV for HER.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Proyectos nacionales MAT2016-77648-R y PID2019-110249RB-I0

Implementing Pair Distribution Function analysis to rationalize the water-splitting activity of Co-phosphonate-derived electrocatalysts.

Pair Distribution Function analysis (PDF) is a total X-ray scattering technique, including the diffuse scattering and the Bragg diffraction. Thus, PDF can be used to characterize structural domains of amorphous solids to investigate local order/properties correlations [1]. Herein, a follow-up of the chemical evolution of pyrophosphate- or phosphide-based Fe/Co electrocatalysts is carried out by synchrotron PDF analysis. The catalysts were prepared from the metal (R,S) 2-hydroxyphosphonoacetates by pyrolysis in N2 (500 ºC and 700 ºC) or 5%-H2/Ar (800 ºC) and studied toward the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Comparison of PDF patterns of the amorphous (500 ºC) and the semicrystalline Fe/Co pyrophosphates (700 ºC) showed that the local order of the amorphous solid is composed of nanoclusters of ~ 7 Å (Figure 1). In contrast, the PDF pattern of the Fe/Co phosphide (800 ºC) is formed by a mixed of the crystalline phases o-Co2P and o-CoP. Differential PDF (d-PDF) analysis of the spent catalysts revealed that, irrespectively of the amorphous or crystalline nature, all pyrolyzed solids transformed under OER operation into biphasic CoO(OH), composed of discrete clusters with size ≤ 20 ÅUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Preparation of N-doped Carbon/Metal Phosphides as Promising Trifunctional Electrocatalysts Toward the OER, ORR and HER

Sustainable energy storage and conversion technologies, such as electrochemical water splitting and fuel cells, attracts increasing attention as alternative processes to advance toward a global decarbonation. However, the high cost, scarcity, and poor stability of the most active electrocatalysts, mainly based on noble metal (Pt, RuO2, IrO2,…), difficult severely their large-scale production and use. In this regard, the development of earth-abundant electrocatalysts, with high activity for the different processes, is needed. Several imidazole-containing metal etidronates, MLIm-n (M2+= Fe, Co, Ni and solid solutions; L= ETID; Im= Imidazole; n= [0, 3]), were prepared using different synthetic procedures. Thermal reduction of MLIm-n in 5%H2–Ar at different temperatures resulted on core–shell N-doped carbon/TMPs with variable content of MP and MxP as crystalline phases. Their electrocatalytic activities have been widely studied by cyclic and linear sweep voltammetry, impedance spectroscopy, transmission electron microscopy, and XPS analysis. Preliminary results reveal that factors such as the presence of the imidazole and the metal coordination environment in the precursor samples determine the final composition and electrochemical properties of the resulting pyrolyzed derivatives. So, the Co2+- derivative, CoLIm-0@800, with a composition CoP/Co2P= 80/20 wt. %, exhibited the best electrocatalytic properties toward OER/ORR/HER as well as good capabilities as anode for overall water splitting in comparison to the expensive reference RuO2 electrocatalyst