Protonic ceramics for electrochemical hydrogen compression

Abstract

The topic of this thesis is designing and characterizing protonic ceramics for the electrochemical hydrogen compression. Protonic-ceramic reactors are attractive for compressed hydrogen production from natural gas because they can effectively integrate steam reforming, hydrogen separation, and electrochemical compression. The current technology requires many unit processes, which introduces significant inefficiency. This thesis first explores protonic-ceramic electrochemical hydrogen compression on tubular cells. Compression to 10 bar was demonstrated, but progress was limited by material availability and scale-up opportunities. A method was developed to fabricate protonic-ceramic cells. The easily-produced samples were characterized and modeled. Discs were made for planar stack development to investigate sealing and reactor design strategies. Scaling up protonic-ceramic electrochemical hydrogen compression is an ongoing challenge. Experiments with tubular cells have compressed H2 up to 10 bar. Tubes are ideal for heavy compression due to strong hoop stress resistance, which is applied from the pressure difference during compression. Unfortunately, tubular geometries do not lend themselves well to stacking, due to poor electrode connections and footprint size. The scarcity and poor compatibility of tubular cells create an opening for new methods to make protonic-ceramic cells. The polymer clay method is a novel processing technique for moldable ceramics in the green state, that fire completely dense. Herein, fabrication of protonic-ceramic membranes is demonstrated in a variety of shapes. Conductivity relaxation measurements between moist and dry reducing conditions on polymer clay coupons were collected and fit to an ambipolar diffusion model. Results demonstrate that polymer clay samples are competitive to samples made by other methods. The final topic of this thesis is how to incorporate efficient cells in robust and durable stacks for electrochemical H2 compression. Planar stack configurations have been heavily explored with other electrochemical devices, including fuel cells. Planar geometries are more conducive to stacking and have tightly integrated electrode connections. Sealing strategies between the bipolar plate and the membrane electrode assembly were explored to determine best practices. Our results demonstrate hydrogen pumping on single cells. While hermetic seals for planar cell stacking remain an ongoing area of study, this study identifies potential solutions.