Novel Nanoporous Composites for Sustainable Energy Applications

Abstract

The accelerating transition toward a low carbon energy system presents urgent
challenges in energy storage and conversion, driven by the intermittency of renewable generation, the need for grid stability, and the global imperative to decarbonise heavy industry, transport, and chemical manufacturing. Hydrogen has emerged as a promising energy carrier owing to its high specific energy and clean end use, yet its widespread implementation remains limited by the difficulty of storing it safely, densely, and efficiently. In parallel, electrochemical technologies such as water electrolysers and metal–air batteries depend heavily on precious metal catalysts, constraining cost effective scale up. Overcoming these limitations requires porous materials with precisely controlled nanostructure, high surface area, tuneable chemistry, and scalable
processability. This thesis investigates polymers of intrinsic microporosity, PIMs, as a versatile class of materials designed to address both hydrogen storage and electrocatalytic challenges. PIMs possess rigid, contorted backbones that generate interconnected micropore networks while retaining solution processability. As part of this study, PIM-1, the archetypal PIM with a BET surface area of 789 m² g⁻¹, was synthesised and subsequently converted via extended acid hydrolysis to PIMCOOH, a nitrogen free analogue that avoids hydrogen cyanide formation during carbonisation. FTIR spectroscopy and elemental
analysis confirm complete nitrile to carboxylic acid conversion, while gas adsorption measurements reveal enhanced microporosity relative to PIM-1, with Dubinin– Radushkevitch (DR) surface areas of 802 m² g⁻¹ and 649 m² g⁻¹, respectively. Additional modification attempts, including esterification, pyridinic nitrogen incorporation, and metal ion coordination, highlight both the opportunities and structural constraints inherent to PIM chemistry. PIMCOOH was then used as a precursor in a systematic carbonisation study spanning 400 to 950 °C. The resulting carbonised materials, cPIMCOOH, exhibit tuneable micro and mesopore hierarchies, progressive development of ultramicroporosity, and the emergence of turbostratic nanographitic domains. Carbonisation rate studies show that slower heating, 1 °C min⁻¹, preserves microporosity and yields a DR surface area of 1011 m² g⁻¹, whereas faster heating, 5 °C min⁻¹, reduces ultramicropore retention to 867 m² g⁻¹. The most graphitic material, cPIMCOOH950, achieves a BET surface area of 813 m² g⁻¹, a CO₂ derived micropore volume of 0.38 mL g⁻¹, and an electrical conductivity
of 2967 S m⁻¹. Electrocatalytic testing showed that this undoped microporous carbon displays activity toward the oxygen reduction and oxygen evolution reactions in alkaline electrolyte, though not toward the hydrogen evolution reaction. It exhibits oxygen reduction onset and half wave potentials of 0.894 V and 0.787 V versus Reversible Hydrogen Electrode (RHE), with a Tafel slope of 264 mV dec⁻¹, and an oxygen evolution Ej=10 of 1.679 V with a Tafel slope of 267 mV dec⁻¹. These performances are comparable to, and in some metrics exceed, those of the commercial high surface area activated carbons MSC30 and MSC30ss.

In parallel, freeze casting methodologies were developed to fabricate PIM based
monoliths for hydrogen storage. Directionally frozen PIM-1 solutions produced
consolidated structures that retain intrinsic microporosity while incorporating aligned macroporous channels. XRCT and SEM characterisation reveal lamellar morphologies, solvent templated macro voids, and thin external skins. It was found that slower freezing rates led to denser more consolidated monolith structures compared to those which experienced a rapid change from ambient to cryogenic temperatures. Composite monoliths containing 20 wt% MSC30 or MSC30ss achieve BET surface areas up to 1418 m² g⁻¹, substantial pore volumes, and measurable high pressure hydrogen uptake, including 4.38 wt% for the PIM 1 MSC30ss monolith at 77 K and 15 MPa. The adsorption behaviour is governed primarily by restricted gas transport through the external skin layers and into the internal pore network, nevertheless, the monoliths exhibit favourable
handling characteristics and mechanical integrity relative to powdered sorbents.

Together, these findings establish PIM derived carbons and freeze cast PIM monoliths as promising and chemically tuneable material platforms for advancing sustainable hydrogen storage and electrocatalytic technologies. The work elucidates clear relationships between polymer chemistry, processing conditions, pore architecture, and functional performance, demonstrating how PIM based materials can be engineered to address critical challenges in clean energy systems.

Date of Award	24 Jun 2026
Original language	English
Awarding Institution	University of Bath Monash University
Supervisor	Tim Mays (Supervisor), Chris Bowen (Supervisor) & Andy Burrows (Supervisor)