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

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

Applications of N,N-bis(phosphonomethyl)glycine-derived Sn4+ or Co2+ phosphonates as proton conductors or energy-conversion electrocatalysts.

Metal phosphonates (MPs), a subclass of coordination polymers, may exhibit acidic groups such as POH, SO3H, COOH, N+-H, etc. Combining these features with electrocatalytically active transition metals, make them highly appealing in the field of fuel cells and electrolysers, as potential proton conductors and/or precursors of electrocatalysts [1,2]. Herein, we investigate the synthesis, characterization and applications of a series of Co2+ and Sn4+ phosphonates derived from glycine-N,N-bis(methylenenphosphonic acid) (BPMGLY). In the case of the tin derivative, an amorphous compound, Sn(C4H11O8NP2)0.75Cl2.5(H2O)2.5 (Sn4+- BPMGLY), was obtained by hydrothermal synthesis. Its pyrolytic treatment at 700 ºC in air led to an amorphous pyrophosphate, (Sn4+- BPMGLY@700). Regarding cobalt phosphonates, three crystalline phases with composition [Co(C4H9O8NP2(H2O)2]·nH2O (n=0, 2) were obtained and their crystal structure were solved. All families were extensively studied as proton conductors across a wide range of temperature and humidity conditions, displaying the Sn4+ derivatives the highest conductivity values of 7.99·10-4 and 6.63·10-3 S·cm-1 for Sn4+-BPMGLY and Sn4+-BPMGLY@700, respectively, at 95 °C and 95% relative humidity (RH) (Figure 1a). Furthermore, the cobalt phosphonates were utilized as precursors for non-precious metal catalysts (NPMCs), by pyrolysis in 5%-H2/Ar at different temperatures and studied as electrocatalysts towards the oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR)Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech