Halloysite-derived nitrogen doped carbon electrocatalysts for anion exchange membrane fuel cells

Yaxiang Lu,Lianqin Wang,Kathrin Preuß,Mo Qiao,Maria-Magdalena Titirici,John Varcoe,Qiong Cai

doi:10.1016/j.jpowsour.2017.10.037

Abstract

Developing the low-cost, highly active carbonaceous materials for oxygen reduction reaction (ORR) catalysts has been a high-priority research direction for durable fuel cells. In this paper, two novel N-doped carbonaceous materials with flaky and rod-like morphology using the natural halloysite as template are obtained from urea nitrogen source as well as glucose (denoted as GU) and furfural (denoted as FU) carbon precursors, respectively, which can be directly applied as metal-free electrocatalysts for ORR in alkaline electrolyte. Importantly, compared with a benchmark Pt/C (20wt%) catalyst, the as-prepared carbon catalysts demonstrate higher retention in diffusion limiting current density (after 3000 cycles) and enhanced methanol tolerances with only 50-60mV negative shift in half-wave potentials. In addition, electrocatalytic activity, durability and methanol tolerant capability of the two N-doped carbon catalysts are systematically evaluated, and the underneath reasons of the outperformance of rod-like catalysts over the flaky are revealed. At last, the produced carbonaceous catalysts are also used as cathodes in the single cell H2/O2 anion exchange membrane fuel cell (AEMFC), in which the rod-like FU delivers a peak power density as high as 703 mW cm−2 (vs. 1106 mW cm−2 with a Pt/C benchmark cathode catalyst).

Highlights

The oxygen reduction reaction (ORR) is a key electrochemical reaction that enables the conversion of oxygen and hydrogen to water in polymer electrolyte fuel cells (PEFCs) [1]
When the mineral template is directly dispersed into the glucose solution, the glucose molecules are adsorbed onto the outer surface of halloysite particles, due to the hydrogen bonding, so that a carbon coating is formed during the hydrothermal carbonization [38]
The larger morphology of the rod-like carbonaceous materials is examined by the scanning transmission electron microscope (STEM), the image in Fig.S1 shows that the catalysts formed a network with the rodlike structure interconnected with each other, which will help improve the anion exchange membrane fuel cell (AEMFC) performance as the network could facilitate the reactant diffusion

Summary

Introduction

The oxygen reduction reaction (ORR) is a key electrochemical reaction that enables the conversion of oxygen and hydrogen to water in polymer electrolyte fuel cells (PEFCs) [1]. It is difficult to fully compare the absolute performances of these catalysts because of the different anion-exchange polymer materials used and the different test conditions applied These results show that the performance of AEMFC (with non-Pt cathode catalysts) needs to be improved. By tailoring the synthesis processes with the same template, N-doped carbonaceous materials with flaky and rodlike morphology were obtained for use as metal-free ORR electrocatalysts in alkaline medium. These catalysts were fabricated into electrodes for testing in single cell H2/O2 AEMFC so that the relationship between structural properties and in situ beginning-of-life ORR performances could be elucidated. Our findings will aid in the future design of further high performance ORR catalysts and fuel cell electrodes based on tailored carbonaceous materials

Chemicals and materials

Materials characterization

Electrochemical measurements

Results and discussion

Conclusions