Heazlewoodite, Ni₃S₂: A Potent Catalyst for Oxygen Reduction to Water under Benign Conditions

Abstract

ABSTRACT:Electrodeposited thin films and nanoparticles of Ni 3 S 2 are highly active, poison and corrosion resistant catalysts for oxygen reduction to water at neutral pH. In pH 7 phosphate buffer, Ni 3 S 2 displays catalytic onset at 0.8 V vs the reversible hydrogen electrode, a Tafel slope of 109 mV/decade, and high Faradaic efficiency for four--electron reduction of O 2 to water. Under these conditions, the activity and stability of Ni 3 S 2 exceeds that of polycrystalline platinum and manganese, nickel, and cobalt oxides illustrating the catalytic potential of pairing labile first row transition metal active sites with a more covalent sulfide host lattice.The interconversion of water and O 2 is an essential chemistry underlying a future renewable energy economy. 1 Nature exe--cutes this kinetically demanding multi--proton, multi--electron interconversion with remarkable selectivity and efficiency. Oxygen evolution is carried out at the Mn 4 Ca co--factor of the oxygen evolving complex of photosystem II 2 whereas oxygen reduction is carried out at the heme/Cu ac--tive site of cytochrome C oxidase 3 and Cu 3 cluster active sites of multicopper oxidases. 4 While these catalysts operate effi--ciently and selectively under benign conditions of neutral pH and ambient temperature and pressure, precious and base metal containing heterogeneous catalysts typically require highly alkaline or acidic electrolytes ( Figure 1).The paucity of heterogeneous electrocatalysts capable of efficient oxygen reduction at neutral pH 5 arises from two seemingly divergent kinetic/materials requirements: 1) the catalyst must remain active in the presence of buffering elec--trolytes that are required to maintain neutral pH stability and deliver protons to drive the proton--coupled electron transfer (PCET) activation of O 2 6 and 2) the catalyst must resist protolytic corrosion under reducing conditions. Pre--cious metal catalysts such as Pt and Au meet the latter re--quirement but also strongly adsorb buffering electrolyte ions such as phosphate, degrading their catalytic efficiency. 7 In contrast, low valent mid to late first row transition metal ions are substitutionally labile, 8 allowing them to meet the first requirement, but this very property makes their corre--sponding oxides unstable with respect to corrosion in all but highly alkaline environments. 9Unlike metal oxides, bonding in transition metal sulfides is more covalent, inhibiting their corrosion under similar con--ditions. 10 Thus, we envisioned that both of the above re--quirements could be met if a labile first row transition metal active site ion can be exposed at the surface of a sulfide host lattice. Here, we illustrate the effectiveness of this design strategy by uncovering a novel earth abundant catalyst for oxygen reduction at neutral pH, the heazlewoodite phase of nickel sulfide, Ni 3 S 2 . Under phosphate buffered neutral pH conditions, Ni 3 S 2 outperforms state of the art ORR catalysts including MnO x and platinum owing to its unique combina--tion of labile ...

Monodisperse cobalt sulfides embedded within nitrogen-doped carbon nanoflakes: an efficient and stable electrocatalyst for the oxygen reduction reaction

“…4 Therefore, great efforts have been devoted to searching for cost-effective non-precious metal or even metalfree catalysts for ORR in these energy conversion devices. Transition metal sulfides (TMSs) usually exhibiting higher conductivity compared with their oxide counterparts have recently attracted great attention for applications in electrocatalysts, [5][6][7] supercapacitors, 8,9 lithium-ion batteries, 10,11 and solar cells. 12,13 Cobalt sulfides have shown promise amongst all TMSs displaying the highest catalytic activity for ORR.…”

Biomass Derived N-Doped Porous Carbon Supported Single Fe Atoms as Superior Electrocatalysts for Oxygen Reduction

“…As potential non-PGM catalysts to replace Pt-based catalysts, the supported transition metal nanoparticles (e.g., metal oxides, metal sulfides, and metal carbide) have been widely studied for various types of heterogeneous catalysts. [11][12][13] For these catalysts, the size control and chemical modification of metal particles are the critical factors in determining the ORR performance. [14][15][16] Decreasing the nanoparticle size to the atomic scale, the single transition metal atoms with unsaturated-coordination often function as the catalytically active sites for ORR (e.g., Fe-N x -C y and Co-N x -C y moieties).…”

Nickel sulfide thin films and nanocrystals synthesized from nickel xanthate precursors

“…Ni 3 S 2 (heazlewoodite) is a Pauli paramagnetic metal [20] with a stable rhombohedral crystal structure [21] and displays catalytic activity in water splitting reactions [7,8]. Metallic Ni 3 S 4 (polydymite) crystallizes in the cubic spinel structure and shows itinerant electron ferrimagnetism [22].…”

“…Among these are solid-state reactions [24,25], physical vapor and atomic layer depositions [14,26], laserinduced reactions [27], electrochemical processes [8], solvo-and hydrothermal routes [2,4,[11][12][13], spray pyrolysis [16], solution-based processes at room temperature [6,22], or microwave-assisted syntheses [3,5].…”