Water assisted high proton conductance in a highly thermally stable and superior water-stable open-framework cobalt phosphate

Abstract

Proton-conducting materials show important technological applications as key components in energy conversion, electrochemical sensing and electrochromic devices; the exploration for new types of proton-conducting materials is crucial for the development of efficient electrochemical devices. In this study, we investigated the proton transport nature of an inorganic-organic hybrid crystal of open-framework cobalt phosphate, (CNH)CoPO. The structure of the hybrid crystal consists of the [CoPO] anionic framework, and the proton carriers, Hen cations (en = ethylenediamine), are located in the pores to compensate the negative charges of the inorganic framework. The open-framework is thermally stable up to 653 K (380 °C) at least, and also shows superior water stability. The open-framework exhibits negligible conductance in an anhydrous environment even at 473 K; however, there is evident water-assisted proton conduction. The conductivity reaches 2.05 × 10 S cm at 329 K and 98% RH. Such high proton conductivity can compete with numerous state-of-the-art MOFs/PCPs-based proton conductors, and this material has promising applications in diverse electrochemical devices.

Hydrogen Production Improvement on Water Decomposition Through Internal Interfacial Charge Transfer in M3(PO4)2-M2P2O7 Mixed-Phase Catalyst (M = Co, Ni, and Cu)

“…Characteristics of M 3 (PO 4 ) 2 -M 2 P 2 O 7 Mixed-Phase Catalysts Figure 1 shows X-ray diffraction (XRD) patterns of the as-synthesized catalysts. A sample of cobalt phosphate was shown to have a consistent pattern with the crystal structure of Co 3 (PO 4 ) 2 in a monoclinic crystal system [27], and a small XRD peak, belonging to the cobalt phosphate hydrate (monoclinic, P21/n), was also found at 33 • . Nickel phosphate particles mostly show an XRD pattern of Ni 3 (PO 4 ) 2 in a monoclinic crystal system with a space group of P21/a, although the Ni 2 P 2 O 7 phase of the monoclinic crystal system with the P21/c space group was also mixed [28].…”

Construction of Strandberg‐Type Polyoxometalate‐Based Inorganic‐Organic Hybrid Material with Water‐Assisted Proton Conductivity

“…At a certain temperature, humidity affects the rearrangement of the hydrogen bond network without changing the crystal skeleton. It can be concluded that at a certain critical temperature (58 °C), water molecules adsorbed in the crystal lattice cause a change in the hydrogen bonds arrangement, leading to obvious changes of proton conductivity and activation energy at 97% RH …”

“…It can be concluded that at a certain critical temperature (58°C), water molecules adsorbed in the crystal lattice cause a change in the hydrogen bonds arrangement, leading to obvious changes of proton conductivity and activation energy at 97% RH. [28] Based on the above experiments, the effect of temperature on the proton conductivity of the material is explained. In the high temperature range (58°C -98°C), the proton conductivity increases significantly, and the activation energy decreases significantly.…”

“…[28,29] For example, Ren's group published a (C 2 N 2 H 10 ) 0.5 CoPO 4 organic-inorganic hybrid material as a proton conductor in 2016. The activation energy of this compound showed different activation energy under different temperature range, when the temperature is lower than 41°C, the activation energy is 0.96 eV, and the activation energy is 1.01 eV when the temperature is higher than 41°C; [28] In 2014, Liu's group studied the MOF based on lanthanide metal ions: [Eu 2 (CO 3 )(ox) 2 (H 2 O) 2 ]⋅4H 2 O as a proton conductor, and its activation energy in different temperature ranges was 0.49 eV (25 -90°C) and 0.28 eV (100 -150°C). [29] In order to eliminate the accidental error caused by the test, we reperformed the proton conductivity test under the variable temperature range under 97% relative humidity for the sample.…”

A 3D open-framework iron hydrogenophosphate showing high proton conductance under water and aqua-ammonia vapor

“…[1][2][3][4] Recently, proton-conductive of open-framework metal phosphates have been becoming an emerging area in the eld of fuel cells, in virtue of their porous structure, good proton carriers and hydrogen-bond supported nets, etc. [5][6][7][8][9][10][11] Similar to metal-organic frameworks (MOFs), [12][13][14][15][16][17][18] open-framework metal phosphates have a designable porous structure, in which the channel can provide an efficient path for proton transmission; then usually inorganic metal skeletons are negatively charged, the counter ions in the channels such as NH 4 + , enH 2 + are good proton carriers and also help to establish efficient hydrogen-bonding networks for proton hopping or moving. Furthermore, the rigid framework of metal phosphates, which consist of metals and phosphates, endow them with better water and chemical stability than MOFs.…”