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The necessity of Earth-abundant low-cost catalysts with activity similar to noble metals such as platinum is indispensable in order to realize the production of hydrogen through electrolysis of water. Herein, we report a relatively low-cost NiAg0.4 3D porous nanocluster catalyst whose activity matches with that of the state-of-the-art Pt/C in 1 M KOH solution. The catalyst is designed on the principle of creating an interface between a metal having a positive Gibbs energy of hydrogen adsorption and a metal of negative Gibbs energy based on the volcano plot, to tune the Gibbs energy of hydrogen adsorption near zero for enhanced hydrogen evolution. The synthesized NiAg0.4 3D porous nanoclusters are comprised of nanoparticles of lateral dimension ∼50 nm forming a 3D porous network with pores of 10 nm–80 nm. A high-resolution transmission electron microscopy image reveals the epitaxial growth of Ag (200) on the Ni (111) plane leading to the creation of abundant interfaces between the Ni and Ag lattices. The catalyst needs a low overpotential of 40 mV@10 mA cm−2 with a Tafel slope of 39.1 mV dec−1 in 1 M KOH solution. Furthermore, the catalyst exhibits a high specific activity of 0.1 mA cm−2(ECSA) at an overpotential (η) of 45 mV which matches with the specific activity of Pt/C 20% wt. catalyst (0.1 mA cm−2@η = 26 mV). Density functional theory calculations reveal that the Ni–Ag interface furnishes a pathway with a reduced Gibbs energy of adsorption of −0.04 eV, thus promoting enhanced hydrogen evolution. In summary, this study reveals excellent HER activity at the Ni–Ag interface.

Highly active catalysts from the earth-abundant metals are essential to materialize the low-cost production of hydrogen through water splitting. Herein, nickel porous networks codoped with Cu and Fe prepared by thermal reduction of presynthesized Cu, Fe-codoped Ni(OH)2 nanowires are reported. The sample consists of nanoparticles of ∼80 nm, which form highly porous network clusters of ∼1 μm with a pore size of 10–100 nm. Among the various doped compositions, the NiCu0.05Fe0.025 porous network exhibits the best catalytic activity with a low overpotential of 60 mV for a hydrogen evolution reaction (HER) in 1 M KOH solution and a specific activity of 0.1 mA cm–2 at 117 mV overpotential calculated based on the electrochemical active surface area (ECSA). The density functional theory calculations reveal that codoping of Fe and Cu into the Ni lattice results in a shift of d-bands of nickel to lower energy levels and thus in the reduced hydrogen adsorption energy (ΔGH = −0.131 eV), which is close to ΔGH for Pt (−0.09 eV). When NiCu0.05Fe0.025(OH)2 nanowires is used as an oxygen evolution reaction (OER) catalyst and is coupled with NiCu0.05Fe0.025 porous networks for overall water splitting, the NiCu0.05Fe0.025∥NiCu0.05Fe0.025(OH)2 catalyst couple achieves a current density of 10 mA cm–2 at 1.491 V, similar to that of the Pt/C∥RuO2 couple and offers a negligible loss in the performance when operated at 20 mA cm–2 for 30 h. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

Porous graphene (PG) devices fabricated in situ from polyimide (PI) adhered onto paper substrates provide a cost-effective and recycling-friendly alternative to re-engineer paper for liquid-based power sources and sensors. However, paper is generally damaged due to heating during the fabrication of PG devices. Here integrated graphene-paper electronics with exceptional thermal control through the proposed thermally localized laser graphitization (LLG) process is demonstrated, employing optimized ultrafast laser writing. LLG enables in situ fabrication of localized porous graphene (LPG) devices (>1775 K) on 65 µm thick PI tape adhered to paper without heating above 348 K. Laser parameters for LLG are predicted using an analytical temperature model and validated experimentally. The LLG is demonstrated by fabricating liquid electrolyte LPG micro-supercapacitors and humidity sensors on liquid susceptible paper. It is envisaged that the scientific concepts proposed and demonstrated here will expedite the development of low-cost, scalable, and chemically robust LPG devices on thermally sensitive substrates. Ministry of Education (MOE) Funding: This work is supported under the research collaboration agreement by Panasonic Factory Solutions Asia Pacific (PFSAP) and Singapore Centre for 3D Printing (SC3DP) (RCA-15/027). V.M.M. also acknowledges the financial support received through COLE-EDB, and MOE Tier 1 Grant RG192/17. S.W.L. acknowledges the support by Academic Research Fund Tier 2 from Ministry of Education, Singapore under ref. no. 2018-T2-1-045.

With an increasing energy consumption rate and rising global population, constructing sustainable energy technologies has become one of the major scientific challenges. Therefore, the development of electrocatalytic conversion technologies that can convert renewable resources, such as water and nitrogen, into value-added chemicals or fuels (e.g., hydrogen and ammonia) can be crucial. A number of transition metal carbides (TMCs) have been investigated over the past few years as effective electrocatalysts for various reactions. This is mainly owing to their unique electronic structures, which leads to high electrical conductivity and chemical stability. Moreover, the reactivity of TMC-based electrocatalysts is highly dependent on their surface and interfacial properties. This review focuses on tuning nanostructures and interfaces to enhance the electrocatalytic activity of TMC-based materials for hydrogen production and nitrogen fixation. The mechanisms behind the surface and interface engineering are discussed, including the synergy effects, facet binding energy, active defects, and low-coordinated sites. In particular, studies on activity enhancement through design of the interfacial phase, composition, and structure in TMC-based electrocatalysts are highlighted. The effective tuning strategies might pave the way for future development of highly active TMC-based electrocatalysts for sustainable energy-related conversion. MOE (Min. of Education, S’pore) Accepted version