Layered Double Hydroxide-Derived Intermetallic Ni₃GaC_0.25 Catalysts for Dry Reforming of Methane

A NiMgGa-layered double hydroxide (NMG-LDH) is synthesized as an efficient catalyst precursor for dry reforming of methane (DRM). NMG-LDH is converted to an intermetallic Ni3Ga/MgO catalyst upon reduction. Compared to a monometallic Ni/MgO catalyst prepared from NiMg-LDH, the Ni3Ga/MgO catalyst exhibits high CH4 (∼48%) and CO2 (∼52%) conversions as well as excellent stability against coking during DRM. The reversible phase transition between intermetallic Ni3Ga and Ni3GaCx is demonstrated by in situ characterizations with the interstitial carbon being involved in the catalytic cycle of DRM to produce CO and H2. According to density functional theory calculations and the experimental study, the LDH-derived Ni3Ga intermetallic catalyst is converted to the Ni3GaC0.25 phase when carbon atoms dissociated from CH4 penetrate into the octahedral interstices of the Ni3Ga lattice during DRM at 600 °C. The formed Ni3GaC0.25 is proven effective in converting the interstitial carbon rapidly into CO to suppress its conversion to the coke, thus improving the stability of the catalyst

High-Performance Electrochemical and Photoelectrochemical Water Splitting at Neutral pH by Ir Nanocluster-Anchored CoFe-Layered Double Hydroxide Nanosheets

Highly efficient electrocatalysts for the oxygen evolution reaction (OER) in neutral electrolytes are indispensable for practical electrochemical and photoelectrochemical water splitting technologies. However, there is a lack of good, neutral OER electrocatalysts because of the poor stability when H+ accumulates during the OER and slow OER kinetics at neutral pH. Herein, we report Ir species nanocluster-anchored, Co/Fe-layered double hydroxide (LDH) nanostructures in which the crystalline nature of LDH-restrained corrosion associated with H+ and the Ir species dramatically enhanced the OEC kinetics at neutral pH. The optimized OER electrocatalyst demonstrated a low overpotential of 323 mV (at 10 mA cm–2) and a record low Tafel slope of 42.8 mV dec–1. When it was integrated with an organic semiconductor-based photoanode, we obtained a photocurrent density of 15.2 mA cm–2 at 1.23 V versus reversible hydrogen in neutral electrolyte, which is the highest among all reported photoanodes to our knowledge

Molecularly Engineered Carbon Platform To Anchor Edge-Hosted Single-Atomic M–N/C (M = Fe, Co, Ni, Cu) Electrocatalysts of Outstanding Durability

A powerful synthetic protocol based on a molecularly engineered anchoring carbon platform (ACP) is reported to stabilize concentrated edge-hosted single-atom catalytic sites of M–N (M = Fe, Co, Ni, Cu) on carbon supports. Polymerization with l-cysteine as an additional organic precursor produces an ACP sheath around the carbon nanotube (CNT)–graphene (GR) hybrid support made of a small domain size with abundant edge sites and doped with sulfur. A few-minute-long microwave pyrolysis anchors strongly the single-atomic M–N moiety on the ACP while suppressing its agglomeration during the high-temperature synthesis and makes the ACP highly graphitized. As a typical example, the edge-hosted single-atomic catalytic sites in Fe–N/S-CNT–GR provide superior pH-independent oxygen reduction reaction (ORR) activity to previously reported Fe–N–C catalysts and commercial Pt/C while demonstrating oxygen evolution reaction (OER) activity in basic conditions similar to known state-of-the-art catalysts. In particular, the Fe–N/S-CNT–GR catalyst is much more stable than commercial Pt/C and Ir/C catalysts during ORR and OER in both base and acid solutions. Inferior stability is a common problem of this type of single-atom heterogeneous catalyst (SAC). An aqueous Zn–air battery with our Fe–N/S-CNT–GR catalyst operates as effectively as the device with the commercial Pt/C–Ir/C catalysts. We believe that our protocol based on the molecularly engineered ACP and microwave pyrolysis can provide a new concept to synthesize a new generation of durable SACs, which could have broad applications in electrochemical energy conversion and storage