Unique Proton Transportation Pathway in a Robust Inorganic Coordination Polymer Leading to Intrinsically High and Sustainable Anhydrous Proton Conductivity

Abstract

Although comprehensive progress has been made in the area of coordination polymer (CP)/metal-organic framework (MOF)-based proton-conducting materials over the past decade, searching for a CP/MOF with stable, intrinsic, high anhydrous proton conductivity that can be directly used as a practical electrolyte in an intermediate-temperature proton-exchange membrane fuel cell assembly for durable power generation remains a substantial challenge. Here, we introduce a new proton-conducting CP, (NH)[Zr(HPO)] (ZrP), which consists of one-dimensional zirconium phosphate anionic chains and fully ordered charge-balancing NH cations. X-ray crystallography, neutron powder diffraction, and variable-temperature solid-state NMR spectroscopy suggest that protons are disordered within an inherent hydrogen-bonded infinite chain of acid-base pairs (N-H···O-P), leading to a stable anhydrous proton conductivity of 1.45 × 10 S·cm at 180 °C, one of the highest values among reported intermediate-temperature proton-conducting materials. First-principles and quantum molecular dynamics simulations were used to directly visualize the unique proton transport pathway involving very efficient proton exchange between NH and phosphate pairs, which is distinct from the common guest encapsulation/dehydration/superprotonic transition mechanisms. ZrP as the electrolyte was further assembled into a H/O fuel cell, which showed a record-high electrical power density of 12 mW·cm at 180 °C among reported cells assembled from crystalline solid electrolytes, as well as a direct methanol fuel cell for the first time to demonstrate real applications. These cells were tested for over 15 h without notable power loss.

Coordination polymer glass from a protic ionic liquid: proton conductivity and mechanical properties as an electrolyte

“…The observed maximum power density was 150 mW cm À2 . Among the fuel cell performance in related conditions at 120 C, this value is higher than that of the reported CP/MOFs, 44,45 xerogels, 46 covalent organic frameworks (COFs), 7,47 and membrane composite of protic ionic liquids 21,40 and as high as the composite of functionalized graphene oxide and Naon (150 mW cm À2 ) measured under humidied conditions (RH ¼ 25%). 48 Furthermore, neat 1 was tested as an electrolyte layer without the PTFE membrane (Fig.…”

Two Highly Stable Proton Conductive Cobalt(II)–Organic Frameworks as Impedance Sensors for Formic Acid

“…The E a values of 1 from the Arrhenius plots upon exposure to 245 ppm of formic acid vapor under 98 and 68 %R Ha re between 0.35 and 0.47 eV (Figure 7d). [8,43] At 98 and 68 %R Ha nd 245 ppm of formic acid vapor,t he E a valuesa re estimated to be 0.48 and 0.61 eV for 2,r espectively ( Figure S42 in the Supporting Information). [8,41] Clearly, for 1, proton conduction is assigned to the Grotthussm echanism at 98 %R H, suggesting that the adsorbed water molecules and formic acidm olecules serve as mediators between the free oxygen sites and coordinated water molecules throughh ydrogen-bond formation;f or 2,p roton conduction occurs through aV ehicle mechanism at 68 %R H, suggesting direct diffusion of foreign protons with water molecules or formic acid molecules.…”

Proton Conductivity of Composite Polyelectrolyte Membranes with Metal‐Organic Frameworks for Fuel Cell Applications

“…Otherwise, bulk conductivity of powdered pellets is normally reported and it takes into account both the intrinsic average conductivity and the surface conductivity effects due to the interparticle contacts. Some comprehensive studies on proton conductivity of the most known MOFs have been already reported during the past decade and the number of very recent examples of reported MOF or related materials (layered hybrid compounds or coordination polymers) with proton conduction properties is continuously growing . However, in the present section, we have only focused on those already used MOFs in MMMs or those displaying potential application as fillers in MMM for PEMFC according to the following criteria: i) high conductivity values (in some case comparable to Nafion) in a wide range of humidity and temperature conditions and ii) high chemical stability in harsh conditions.…”