Nitrogen‐Doped Metal‐Free Carbon Materials Derived from Cellulose as Electrocatalysts for the Oxygen Reduction Reaction

Abstract

Development of metal‐free carbon‐based electrocatalysts for reducing oxygen to water (ORR), preferentially following a 4 electron transfer pathway, is of high importance. We present a two‐step synthesis of N‐doped carbon‐based ORR electrocatalysts by using an efficient thermal treatment of hydrothermally carbonized cellulose in ammonia combining devolatilization, reduction and nitrogen doping. The influence of the synthesis temperature as well as of the ammonia concentration used during the synthesis on the electrocatalytic ORR activity was analyzed using bulk‐ and surface‐sensitive techniques. Correlation of electrocatalytic activity with structural features of the catalysts provided deeper mechanistic understanding and enabled us to optimize the synthesis conditions. The nitrogen‐doped metal‐free catalyst originating from the treatment in 100 % NH3 at 800 °C achieved a current density of −1 mA cm−2 at 0.83 V vs. RHE positioning it among the most active noble‐metal free and biomass‐based ORR catalysts reported so far.

Hydrothermal Carbon/Carbon Nanotube Composites as Electrocatalysts for the Oxygen Reduction Reaction

“…Carbon materials are a promising alternative to Pt-based electrocatalysts. Carbon nanotubes, carbon nanofibers, activated carbons, carbon xerogels, and graphene-based materials have been widely studied as electrocatalysts [6,[9][10][11][12][13][14][15]. Among them, activated carbons are interesting materials, as they can be obtained by low-cost and environmentally friendly routes [16].…”

“…Among them, activated carbons are interesting materials, as they can be obtained by low-cost and environmentally friendly routes [16]. In fact, the use of hydrothermal processes to prepare carbon materials from biomass has emerged recently as an interesting strategy [12,[17][18][19][20]. Biomass is an abundant, low-cost, and environmental-friendly source [21], which makes hydrothermal carbons (HTCs) good candidates to replace Pt-based electrocatalysts [2,8,22].…”

“…Nevertheless, the chemical properties of HTCs need to be modified in order to approach the outstanding electrochemical performance of Pt-electrocatalyst reference materials [23,24]. These modifications can be achieved by the incorporation of heteroatoms like nitrogen, sulfur, phosphorus, or boron and/or advanced carbon materials like graphene oxide or carbon nanotubes (CNTs) [9,12,13,17,[25][26][27][28]. Nitrogen is the most promising heteroatom for ORR, as pyridinic nitrogen favors the bonding of oxygen to the adjacent carbon, while the presence of quaternary nitrogen favors oxygen dissociation [7,29].…”

Graphitic nitrogen in carbon catalysts is important for the reduction of nitrite as revealed by naturally abundant15N NMR spectroscopy

“…Since HF is toxic, we here explore a comparably sustainable route to the synthesis of N-doped carbons and circumvent the applications of HF, and we also involve a renewable cellulose substrate as the carbon precursor. [50][51][52][53][54][55][56] The synthetic pathway is illustrated in Scheme 1. It does not cover all principles of Green Chemistry, 57 as NH 3 is toxic, however, NH 3 is a common base chemical and allows the introduction of high amounts of N. We report an unexpected incorporation of graphitic N in the N-doped carbon and its detection by using 15 N ssNMR spectroscopy.…”

Poly-active centric Co3O4-CeO2/Co-N-C composites as superior oxygen reduction catalysts for Zn-air batteries

“…Therefore, it is highly desirable and still challenging to develop non-precious metal ORR catalysts with comparable catalytic performance and higher stability. Over recent years, a series of non-precious metal catalysts (NPMCs) have been exploited for ORR [13][14][15][16], including metal-free nitrogen-doped carbon materials [17][18][19], nanocarbon/transition-metal compound hybrids [20][21][22] and metal oxides [23][24][25]. Among metal oxides, cobalt trioxide (Co 3 O 4 ) shows good ORR performance but low electrical conductivity.…”