Appendix A. Summary of the model fitting procedure used for random effects for generalized linear mixed model analyses of growth, survival, and reproduction.

Summary of the model fitting procedure used for random effects for generalized linear mixed model analyses of growth, survival, and reproduction

Pomegranate-like N,P-Doped Mo₂C@C Nanospheres as Highly Active Electrocatalysts for Alkaline Hydrogen Evolution

Well-defined pomegranate-like N,P-doped Mo₂C@C nanospheres were prepared by simply using phosphomolybdic acid (PMo₁₂) to initiate the polymerization of polypyrrole (PPy) and as a single source for Mo and P to produce N,P-doped Mo₂C nanocrystals. The existence of PMo₁₂ at the molecular scale in the polymer network allows the formation of pomegranate-like Mo₂C@C nanospheres with a porous carbon shell as peel and Mo₂C nanocrystals well-dispersed in the N-doped carbon matrix as seeds. This nanostructure provides several favorable features for hydrogen evolution application: (1) the conductive carbon shell and matrix effectively prevent the aggregation of Mo₂C nanocrystals and facilitate electron transportation; (2) the uniform N,P-doping in the carbon shell/matrix and plenty of Mo₂C nanocrystals provide abundant catalytically highly active sites; and (3) nanoporous structure allows the effective exposure of active sites and mass transfer. Moreover, the uniform distribution of P and Mo from the single source of PMo₁₂ and N from PPy in the polymeric PPy–PMo₁₂ precursor guarantees the uniform N- and P-co-doping in both the graphitic carbon matrix and Mo₂C nanocrystals, which contributes to the enhancement of electrocatalytic performance. As a result, the pomegranate-like Mo₂C@C nanospheres exhibit extraordinary electrocatalytic activity for the hydrogen evolution reaction (HER) in terms of an extremely low overpotential of 47 mV at 10 mA cm^–2 in 1 M KOH, which is one of the best Mo-based HER catalysts. The strategy for preparing such nanostructures may open up opportunities for exploring low-cost high-performance electrocatalysts for various applications

Component-Controlled Synthesis and Assembly of Cu–Pd Nanocrystals on Graphene for Oxygen Reduction Reaction

Exploring low-cost, high-activity, and long-durability hybrid electrocatalysts for cathodic oxygen reduction reaction (ORR) is vital to advance fuel cells technologies. In this paper, a series of graphene (G)–Cu_<i>x</i>Pd_<i>y</i> (Cu₄Pd, Cu₃Pd, CuPd, CuPd₃, CuPd₄) nanocomposites (G–Cu_<i>x</i>Pd_<i>y</i> NCPs) is obtained by assembly of Cu_<i>x</i>Pd_<i>y</i> alloy nanocrystals (NCs) with controlled component ratios on G nanosheets using the “dispersing–mixing–vaporizing solvent” strategy and used as electrocatalysts for ORR. Compared with pure Cu_<i>x</i>Pd_<i>y</i> NCs, greatly enhanced interfacial electron transfer dynamics are observed in G–Cu_<i>x</i>Pd_<i>y</i> NCPs, which show a strong correlation with the alloy compositions of the NCPs. The electrocatalytic experiments in alkaline solution reveal that the ORR activities of those G–Cu_<i>x</i>Pd_<i>y</i> NCPs are also strongly dependent on alloy components and exhibit a double-volcano feature with variations of alloy components. Among them, G–Cu₃Pd NCPs possess the highest electrocatalytic activity, which is much better than some reported electrocatalysts and commercial Pd/C catalyst and close to Pt/C catalyst. By correlating the Pd 3d binding energies and the sizes of Cu_<i>x</i>Pd_<i>y</i> NCs with the mass-specific activities of G–Cu_<i>x</i>Pd_<i>y</i> NCPs and considering the interfacial electron transfer dynamics, the best catalytic activity of G–Cu₃Pd NCPs may result from the unique electronic structure and the smallest size of Cu₃Pd NCs as well as the strong synergistic effect between G and Cu₃Pd NCs. Moreover, the durability of G–Cu₃Pd NCPs is superior to that of Pt/C catalyst, indicating that they are promising cathodic electrocatalysts for using in alkaline fuel cells

Encased Copper Boosts the Electrocatalytic Activity of N‑Doped Carbon Nanotubes for Hydrogen Evolution

Nitrogen (N)-doped carbons combined with transition-metal nanoparticles are attractive as alternatives to the state-of-the-art precious metal catalysts for hydrogen evolution reaction (HER). Herein, we demonstrate a strategy for fabricating three-dimensional (3D) Cu-encased N-doped carbon nanotube arrays which are directly grown on Cu foam (Cu@NC NT/CF) as a new efficient HER electrocatalyst. Cu nanoparticles are encased here instead of common transition metals (Fe, Co, or Ni) for pursuing a well-controllable morphology and an excellent activity by taking advantage of its more stable nature at high temperature and in acidic or alkaline electrolyte. It is discovered that metallic Cu exhibits strong electronic modulation on N-doped carbon to boost its electrocatalytic activity for HER. Such a nanostructure not only offers plenty of accessible highly active sites but also provides a 3D conductive open network for fast electron/mass transfer and facilitates gas escape for prompt mass exchange. As a result, the Cu@NC NT/CF electrode exhibits superior HER performance and durability, outperforming most of the reported M@NC materials. Furthermore, the etching experiments together with X-ray photoelectron spectroscopy (XPS) analysis reveal that the electronic modulation from encased Cu significantly enhances the HER activity of N-doped carbon. These findings open up opportunities for exploring other Cu-based nanomaterials as efficient electrocatalysts and understanding their catalytic processes

Electronic and Morphological Dual Modulation of Cobalt Carbonate Hydroxides by Mn Doping toward Highly Efficient and Stable Bifunctional Electrocatalysts for Overall Water Splitting

Developing bifunctional efficient and durable non-noble electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly desirable and challenging for overall water splitting. Herein, Co–Mn carbonate hydroxide (CoMnCH) nanosheet arrays with controllable morphology and composition were developed on nickel foam (NF) as such a bifunctional electrocatalyst. It is discovered that Mn doping in CoCH can simultaneously modulate the nanosheet morphology to significantly increase the electrochemical active surface area for exposing more accessible active sites and tune the electronic structure of Co center to effectively boost its intrinsic activity. As a result, the optimized Co₁Mn₁CH/NF electrode exhibits unprecedented OER activity with an ultralow overpotential of 294 mV at 30 mA cm^–2, compared with all reported metal carbonate hydroxides. Benefited from 3D open nanosheet array topographic structure with tight contact between nanosheets and NF, it is able to deliver a high and stable current density of 1000 mA cm^–2 at only an overpotential of 462 mV with no interference from high-flux oxygen evolution. Despite no reports about effective HER on metal carbonate hydroxides yet, the small overpotential of 180 mV at 10 mA cm^–2 for HER can be also achieved on Co₁Mn₁CH/NF by the dual modulation of Mn doping. This offers a two-electrode electrolyzer using bifunctional Co₁Mn₁CH/NF as both anode and cathode to perform stable overall water splitting with a cell voltage of only 1.68 V at 10 mA cm^–2. These findings may open up opportunities to explore other multimetal carbonate hydroxides as practical bifunctional electrocatalysts for scale-up water electrolysis