Tunable crystal structure and proton conductivity of lanthanide nitrilotrismethylphosphonates

Metal phosphonates are multifunctional solids with remarkable stability and proton conducting properties owing to their structure is usually composed of extended hydrogen-bond networks that favor proton transfer pathways [1]. Moreover, these properties can be enhanced by appropriate modification of the synthesis conditions [2, 3]. In this communication, a new family of isostructural 2D layered compounds based on lanthanide nitrilotris-methylphosphonates is reported. These compounds have been isolated at room temperature and have the general formula Ln[N(CH2)3(PO3H2)2(PO3H)(H2O)]SO4·2H2O (Ln= Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Yb). The coordination environment of Ln3+ is composed by eight oxygen atoms from three different ligands and two oxygens from bound waters. This connectivity creates positive charged layers connected to sulfate ions through hydrogen-bonds. These compounds show promising proton conductivity with values ranging between 7.6·10-2 and 3.8·10-2 S·cm-1 at 80 °C and 95% RH and low activation energy corresponding to Grotthuss-type proton transfer mechanism. In addition, a structural transformation occurs at T > 70 °C accompanied by a remarkable enhanced conductivity. Studies on the structure-properties relationships will be discussed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. MINECO: MAT2016-77648-R Junta Andalucía: P12-FQM-1656 y FQM-11

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

New multifunctional sulfonato-containing metal phosphonates proton conductors

Anchoring of acidic functional groups to organic linkers acting as ligands in metal phosphonates has been demonstrate to be a valid strategy to develop new proton conductor materials, which exhibit tunable properties and are potentially applicable to proton exchange membranes, such as those used in PEMFCs [1,2]. In this work, the structural and proton conductivity properties of several families of divalent and trivalent metal amino-sulfophosphonates are presented. The chosen ligand, (H2O3PCH2)2-N-(CH2)2-SO3H, was reacted with the appropriate metal salt using highthrough-put screening and/or microwave-assisted synthesis. Different crystal structures haven been solved displaying a variety of metal ligand coordination modes, in whose frameworks acidic groups contribute to create strong H-bond networks; together with lattice and bound water molecules. Proton conductivity values oscillate between 10-4 and 10-2 S.cm-1, at 80 ºC and 95 % relative humidity, most of them showing activation energies characteristic of a Grotthuss-type proton transport mechanism.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. MINECO: MAT2016-77648-R Junta de Andalucía: P-12-FQM-1656 y FQM-11

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

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

Zinc(II), cobalt(II) and manganese(II) networks with phosphoserine ligand: Synthesis, crystal structures magnetic and conduction properties

A series of zinc(II), cobalt(II) and manganese(II) coordination networks with the phosphoserine ligand (Pser) is synthesized and characterized. Whereas in compounds 1 and 2 with the general formula [M(Pser)]n [M = Zn (1) and Co(2)], the metal(II) ion presents a tetrahedral geometry, in [Co(Pser)(H2O)2]n (3) and [Mn(Pser)(H2O)]n (4)], the metal(II) ions are in a distorted octahedral geometry. The 3D frameworks are formed by inorganic layers built up from MO4 or MO6 polyhedra and phosphate groups. These layers are linked by the carboxylate groups of the phosphoserine ligand. The presence of extended hydrogen bonding stabilizes the 3D network and favors the proton transfer leading to moderate proton conductors. The highest proton conductivity, 2.70·10−5 S cm−1 (at 80 ºC and 95% RH), is obtained for compound 3. Temperature dependent magnetic susceptibility measurements for 2−4 reveal predominant antiferromagnetic interactions between the paramagnetic metal(II) ions.Proyectos MAT2013-41836-R y MAT2016-77648-R del MINECO, y proyecto (P12-FQM-1656) de la Junta de Andalucía

Synthesis and properties of novel lanthanide carboxyphosphonates

Metal phosphonates are essentially acidic solids featured by groups such as P-OH, -COOH, etc. The presence of bound and lattice water favors the formation of H-bond networks, which make these compounds appropriate as proton conductors, attractive for proton exchange membranes (PEMs) of Fuel Cells. Moreover, these properties can be enhanced by appropriate modification of the synthesis conditions. We report here, general characteristics of three new series of isostructural compounds resulting from the combination of the polyfunctional 5-(dihydroxyphosphoryl) isophthalate acid with lanthanide ions. All compounds were synthesized under hydrothermal conditions and their crystal structures were solved from powder X-ray diffraction data using synchrotron radiation. In contrast with Series III compounds, which exhibit a layered structure, Series I and II present pillared frameworks. All these compounds contain water molecules that contribute to the formation of H-bond networks. Upon exposure to ammonia vapour, from an aqueous solution, solid state transformations are observed which are accompanied of an enhancement of their proton conductivity properties.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec