The hydrogen evolution reaction, 2H(+) + 2e(–) → H2, and its converse, the hydrogen oxidation reaction, H2 → 2H(+) + 2e(–), are central to any realization of a hydrogen economy. Various forms of carbon have been used for decades as the precious metal catalyst support in these reactions. Here we report the unexpected result that single-wall carbon nanotubes and some graphitic carbons, activated by brief exposure to electrochemical potentials that induce hydrogen evolution in intercalating acids combined with extended soak times in such acids, acquire an activity for these reactions that exceeds that of known nonprecious metal catalysts.

The perspective of generating new colors commonly difficult to attain such as cyan blue and greens of various tones and saturations has motivated the design of conjugated polymer finely tuned in their molecular structure to reassemble the optical features desired in the context of non-emissive electrochromic device (ECD) applications. Herein, we report on a series of soluble donor−acceptor (DA) conjugated polymers involving 3,4-dioxythiophenes (DOTs) and 2,1,3-benzothiadiazole (BTD) constructed in combination with unsaturated linkages, namely ethynylene and trans-ethylene, and compare these to their fully polyheterocyclic DA control analogues with careful emphasis on optical, electrochemical, and electrochromic (EC) properties. As confirmed by spectroelectrochemical analysis, ethynylene linkers hindered the formation of a defined bipolaronic transition in the near-IR and were thus found disruptive with respect to the EC potential of their subsequent alternating copolymers. On the other hand, the presence of trans-ethylene spacers incorporated in the DA polymeric backbones allowed further narrowing of the energy gap so that new colors distinct from that exhibited by the control polymers were accessed including saturated green, a complementary color in the realization of polymeric EC displays. Systematic spectroelectrochemical analysis of each novel DA polymer is provided that offers clear evidence of the requirement for conformational freedom and stable quinoidal geometries upon electrochemical oxidation as cathodically coloring electrochromic polymers (ECPs) are switched reversibly to their transmissive doped state.

Black-to-transmissive switching polymer electrochromic devices (ECDs) were designed using a set of spray-processable cathodically coloring polymers, a non-color-changing electroactive polymer poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) as the charge-compensating counter electrode, and a highly conducting gel electrolyte (6.5 mS cm(-1)). The color "black" was obtained by utilizing (1) individual copolymers absorbing across the visible spectrum, and (2) blends and bilayers of several polymer electrochromes with complementary spectral absorption. Neutral-state black and ink-like dark purple-blue (or "ink-black") donor-acceptor (DA) copolymers composed of the electron-donor 3,4-propylenedioxythiophene (ProDOT) and the electron-acceptor 2,1,3-benzothiadiazole (BTD) building units, which possess relatively homogeneous absorption profiles across the visible spectrum, were chosen for their propensity to switch to transmissive states upon electrochemical oxidation. A blend of magenta and cyan polymers (PProDOT-(CH(2)OEtHx)(2) and P(ProDOT-BTD-ProDOT), respectively) was produced with the goal of generating the same dark purple-blue color as that obtained with the "ink-black" DA copolymer. While the multi-polymer ECDs demonstrate high contrasts (up to 50%T), and switch from a saturated purple-blue color (L*=32, a*=13, b*=-46) to a light green-blue transmissive state (L*=83, a*=-3, b*=-6), devices made with the DA electrochromic copolymers switch more than two times faster (0.7 s to attain 95% of the full optical change) than those involving the polymer blends (1.6 s), and exhibit more neutral achromatic colors (L*=38, a*=5, b*=-25 for the colored state and L*=87, a*=-3, b*=-2 for the bleached state, correspondingly). The results obtained suggest that these materials should prove to be applicable in both transmissive- (window-type) and reflective-type ECDs.