Catalyst development for the efficient direction of electrocatalytic water splitting with much less overpotential is crucial for meeting large-scale hydrogen generation. Being highly abundant and cost-effective, 3d transition-metal-based catalysts show promising activities in alkaline conditions. In this work, bimetallic nickel−cobalt carbonate hydroxide hydrate (NiCo-CHH) was prepared by a co-precipitation method with varying molar ratios of Ni/Co of 0.5:1, 1:1, and 1.5:1, which were analyzed for oxygen evolution reaction (OER) study in both alkaline (1 M KOH) and near-neutral (1 M NaHCO 3 ) media. For OER in 1 M KOH, NiCoCHH 1:1 required overpotential of just 238 mV at 10 mA cm −2 current density compared to other ratios of 0.5:1 and 1.5:1, which required 290 and 308 mV, respectively. Similarly, in 1 M NaHCO 3 , NiCoCHH 1:1 required an overpotential of 623 mV to reach 10 mA cm −2 . A post-OER study confirmed the formation of NiOOH during OER. The observed faradaic efficiency was nearly 95.21% for the NiCoCHH 1:1 catalyst. A two-electrode setup with NiCoCHH 1:1∥Pt required just 312 mV as an overpotential at 10 mA cm −2 . These kinds of comparative studies can be used in other 3d transition-metal-based catalysts for OER in the future.
Transition metals have been recognized as excellent and efficient catalysts for the electrochemical nitric oxide reduction reaction (NORR) to value‐added chemicals. In this work, a class of core–shell electrocatalysts that utilize nickel nanoparticles in the core and nitrogen‐doped porous carbon architecture in the shell (Ni@NC) for the efficient electroreduction of NO to ammonia (NH3) is reported. In Ni@NC, the NC prevents the dissolution of Ni nanoparticles and ensures the long‐term stability of the catalyst. The Ni nanoparticles involve in the catalytic reduction of NO to NH3 during electrolysis. As a result, the Ni@NC achieves a faradaic efficiency (FE) of 72.3% at 0.16 VRHE. The full‐cell electrolyzer is constructed by coupling Ni@NC as cathode for NORR and RuO2 as an anode for oxygen evolution reaction (OER), which delivers a stable performance over 20 cycles at 1.5 V. While integrating this setup with a PV‐electrolyzer cell, and it demonstrates an appreciable FE of >50%. Thus, the results exemplify that the core–shell catalyst based electrolyzer is a promising approach for the stable NO to NH3 electroconversion.
Metallic Ni nanoparticles wrapped with an N-doped carbon shell as a stable catalyst for the electrochemical reduction of NO to NH3 with high efficiency is described.
Transition metals have been recognized as excellent and efficient catalysts for transforming gaseous molecules into value-added chemicals. Electrochemical ammonia synthesis through the atmospheric reduction of nitrogen and nitrogen oxide is a promising method for sustainable fertilizer and carbon-free hydrogen energy carriers. However, it is a great challenge to main the activity and stability of the catalyst due to its corrosive nature and vigorous reaction conditions involved in the electrochemical transformations.
We report stable core-shell electrocatalysts that utilize transition metal nanoparticles in the core and nitrogen-doped porous carbon architecture in the shell for the efficient electroreduction of N2 and NO to ammonia (NH3). The carbon shell prevents the dissolution of Ni nanoparticles. It ensures the long-term stability of the catalyst, whereas the Ni nanoparticles involve in the catalytic reduction of NO to NH3 during electrolysis. The catalyst images reveal a core-shell structure composed of dark metallic spherical particles at the core and layered carbon as a shell surrounding the nanoparticles (Fig. 1a). A broad particle size distribution of 15 nm to 50 nm was observed, and the core-shell particles were interconnected by a smooth carbon matrix. The heteroatom content and the shell thickness strongly influence the catalytic activity. A high faradaic efficiency (FE) of 72.3% at 0.16 VRHE is achieved (Fig. 1b). Moreover, the full-cell electrolyzer was constructed by coupling developed cathodes and commercial RuO2 as anode for oxygen evolution reaction, which delivered a stable performance over several cycles at 1.5 V. Further, we demonstrate the solar to fuel transformation by integrating with a PV-electrolyzer cell, it presented an appreciable FE of >50%.
Fig. 1. (a) TEM image of core-shell catalyst, (b) comparison of FE and NH3 yields on various electrocatalysts for the nitric oxide reduction reaction.
Figure 1
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